An hour span if we want. What period of time is called days. How many hours, minutes and seconds are in a day, and why it happened. Use to indicate time of day. What is the name of the hourly interval. Chapter of the thirteenth

The length of bodies in different reference systems

Let's compare the length of the rod in inertial reference frames K and K"(Fig.). Suppose that the bar located along the coinciding axes xand x "rests in the system K "... Then determining its length in this system is not a problem. You need to attach a scale ruler to the rod and determine the coordinate x " 1 one end of the bar and then the coordinate x " 2 the other end. The difference in coordinates will give the length of the rod  0 in the system K ":  0 = x " 2 ‑ x " 1 .

The rod rests in the systemK "... About the systemKhe moves with speedvequal to the relative speed of the systemsV.

Designation Vwe will use it only in relation to the relative speed of reference frames. Since the rod is moving, it is necessary to simultaneously read the coordinates of its ends x 1 and x 2 at some point in time t... The difference in coordinates will give the length of the bar  in the system K:

 = x 2 ‑ x 1 .

To compare the lengths  and  0, you need to take that of the Lorentz transformation formulas that connects the coordinates x, x "and time tsystems K... Substitution of coordinates and time values \u200b\u200binto it leads to expressions

(we substituted its value for β). Replacing the coordinate differences with the bar lengths, and the relative velocity Vsystems Kand K "the rod speed equal to it vwith which it moves in the system K, we arrive at the formula

Thus, the length of the moving rod turns out to be less than that which the rod possesses at rest. A similar effect is observed for bodies of any shape: in the direction of motion, the linear dimensions of the body contract the more, the greater the speed of motion. This phenomenon is called Lorentz (or Fitzgerald) contraction. The transverse dimensions of the body do not change. As a result, for example, the ball takes the shape of an ellipsoid flattened in the direction of motion. It can be shown that visually this ellipsoid will be perceived as a ball. This is due to the distortion of the visual perception of moving objects, caused by the difference in the times that light spends on the path from variously distant points of the object to the eye. Distortion of visual perception leads to the fact that the moving ball is perceived by the eye as an ellipsoid elongated in the direction of movement. It turns out that the change in shape due to the Lorentz contraction is exactly compensated by the distortion of visual perception.

Time lapse between events

Let the system K "at the same point with the coordinate x "occur at times t " 1 and t " 2 some two events. This can be, for example, the birth of an elementary particle and its subsequent decay. In system K "these events are separated by a period of time

t" = t" 2 ‑ t" 1 .

Find the time interval  tbetween events in the system K, with respect to which the system K "moves with speed V... For this, we define in the system Kmoments in time t 1 and t 2 corresponding to the moments t " 1 and t " 2 and form their difference:

t = t 2 - t 1 .

Substitution of coordinates and times into it leads to the expressions

If events occur with the same particle resting in the system K ", then  t "= t " 2 -t " 1 is a time interval, measured by a clock, stationary relative to the particle and moving with it relative to the system Kwith speed vequal to V(recall that the letter Vwe only denote the relative speed of the systems; particle and clock speeds will be denoted by the letter v). The time counted by the clock moving with the body is called own time of this body and is usually denoted by the letter τ. Therefore,  t "\u003d τ. The quantity  t== t 2 - t 1 represents the time interval between the same events, measured by the system clock K, relative to which the particle (together with its clock) moves with the speed v... With that said

It follows from the resulting formula that own time is less than the time counted by the clock moving relative to the body (it is obvious that the clock stationary in the system K, move relative to the particle with a speed - v). In whatever frame of reference the particle's motion is considered, the interval of proper time is measured by the clock of the system in which the particle is at rest. Hence it follows that the proper time interval is invariant, i.e., a quantity that has the same value in all inertial reference frames. From the point of view of an observer "living" in the system K, tis the time interval between events, measured by a stationary clock, and τ is the time interval measured by a clock moving at a speed v... Since τ< t, we can say that a moving clock runs slower than a resting clock. This is confirmed by the following phenomenon. In the composition of cosmic radiation there are unstable particles born at an altitude of 20-30 km, called muons. They decay into an electron (or positron) and two neutrinos. The intrinsic lifetime of muons (that is, the lifetime measured in the system in which they are stationary) averages about 2 μs. It would seem that even moving at a speed very little different from c, they can only travel a path equal to 3 · 10 8 · 2 · 10 -6 m. However, as measurements show, they manage to reach the earth's surface in significant numbers. This is due to the fact that muons move at a speed close to c... Therefore, their lifetime, measured by a clock stationary relative to the Earth, turns out to be much longer than the proper lifetime of these particles. Therefore, it is not surprising that the experimenter observes the range of muons significantly exceeding 600 m.For an observer moving with muons, the distance to the Earth's surface is reduced to 600 m, so muons have time to fly this distance in 2 μs.

It does not take much effort of self-observation to show that the last alternative is true and that we cannot be aware of either duration or extension without any sensory content. Just as we see with closed eyes, in the same way, with complete distraction from the impressions of the external world, we are nevertheless immersed in what Wundt somewhere called the "half-light" of our general consciousness. The beating of the heart, breathing, the pulsation of attention, scraps of words and phrases sweeping through our imaginations - that is what fills this vague area of \u200b\u200bconsciousness. All these processes are rhythmic and are recognized by us in an immediate wholeness; breathing and pulsation of attention represent a periodic alternation of rising and falling; the same is observed in the heartbeat, only here the oscillation wave is much shorter; words rush through our imaginations not alone, but in groups. In short, no matter how we try to free our consciousness from any content, some form of a changing process will always be recognized by us, representing an element that cannot be removed from consciousness. Along with the consciousness of this process and its rhythms, we are also aware of the period of time it occupies. Thus, the awareness of change is a condition for the awareness of the passage of time, but there is no reason to assume that the flow of absolutely empty time is enough to generate in us the awareness of change. This change should represent a known real phenomenon.

Estimating longer periods of time. Trying to observe in consciousness the flow of empty time (empty in the relative sense of the word, according to the above), we mentally follow it with interruptions. We say to ourselves: "now", "now", "now" or: "more", "more", "more" as time passes. The addition of known units of duration is the law of the discontinuous flow of time. This discontinuity, however, is due only to the fact of discontinuity in perception or apperception of what it is. In fact, the sense of time is as continuous as any other similar sensation. We call separate pieces of continuous sensation. Each of our "more" marks some finite part of the expiring or expired interval. According to Godgson's expression, sensation is a measuring tape, and apperception is a dividing machine that marks intervals on the tape. Listening to a continuously monotonous sound, we perceive it with the help of an intermittent pulsation of apperception, mentally saying: "the same sound", "the same", "the same"! We do the same by observing the passage of time. Having begun to mark intervals of time, we very soon lose the impression of their total amount, which becomes extremely vague. We can determine the exact amount only by counting, or following the movement of the hour hands, or using some other method of symbolizing time intervals.

The concept of periods of time exceeding hours and days is completely symbolic. We think about the sum of known intervals of time, or imagining only its name, or mentally going over the largest events of this period, without pretending to reproduce mentally all the intervals that form a given minute. No one can say that he perceives the time interval between the present century and the first century BC as a longer period in comparison with the time interval between the present and the 10th centuries. True, in the imagination of the historian, a longer period of time evokes a greater number of chronological dates and a greater number of images and events and therefore seems richer in facts. For the same reason, many people claim that they directly perceive a two-week period as longer than a week. But here, in fact, there is no intuition of time at all, which could serve as a comparison.

More or less dates and events are in this case only a symbolic designation of the greater or lesser duration of the interval they occupy. I am convinced that this is the case even in the case when the compared time intervals are no more than an hour or so. The same thing happens when we compare spaces of several miles. The criterion for comparison in this case is the number of length units contained in the compared intervals of space.

Now it is most natural for us to turn to an analysis of some of the well-known fluctuations in our estimate of the length of time. Generally speaking, a time filled with varied and interesting impressions seems to pass quickly, but, having passed, seems to be very long when remembered about it. On the contrary, time, which is not filled with any impressions, seems to be long, passing, and when it does, it seems to be short. A week devoted to traveling or visiting various sights barely leaves the impression of one day in memory. When you mentally look at the elapsed time, its duration seems to be more or less, obviously, depending on the number of memories it evokes. The abundance of objects, events, changes, numerous divisions immediately make our view of the past broader. Vapidness, monotony, lack of novelty make it, on the contrary, narrower.

As we age, the same period of time begins to seem shorter to us - this is true for days, months and years; about the clock - doubtful; as for minutes and seconds, they seem to always appear to be approximately the same length. For the old man, the past, in all likelihood, does not seem longer than it seemed to him in childhood, although in fact it may be 12 times longer. For most people, all the events of adulthood are so familiar that individual impressions are not retained for long in the memory. At the same time, more and more earlier events begin to be forgotten due to the fact that memory is not able to retain such a number of separate definite images.

That's all I wanted to say about the apparent shortening of time when looking at the past. Present tense seems shorter when we are so absorbed in its content that we do not notice the flow of time itself. A day filled with vivid impressions is quickly sweeping by in front of us. On the contrary, a day full of expectations and unsatisfied desires for change will seem like an eternity. Taedium, ennui, Langweile, boredom, boredom are words for which there is a corresponding concept in every language. We become bored when, due to the relative poverty of the content of our experience, attention is focused on the very passage of time. We expect new impressions, we prepare to perceive them - they do not appear, instead of them we experience an almost empty period of time. With the continuous numerous repetitions of our disappointments, the length of time itself begins to be felt with extraordinary power.

Close your eyes and ask someone to tell you when one minute has passed: this minute of complete absence of external impressions will seem incredibly long to you. It is as exhausting as the first week of sailing on the ocean, and you are involuntarily surprised that humanity could go through incomparably longer periods of painful monotony. The whole point here lies in directing attention to the sense of time per se (in itself) and in the fact that attention in this case perceives extremely subtle subdivisions of time. In such experiments, the colorlessness of impressions is unbearable for us, because excitement is an indispensable condition for pleasure, while the feeling of empty time is the least exciting experience of all that we can have. According to Volkmann, the taedium represents, as it were, a protest against the entire content of the present.

The sense of the past tense is the present. Considering the modus operandi of our knowledge of temporal relationships, one might think at first glance that this is the simplest thing in the world. The manifestations of inner feeling are replaced in us by one another: they are recognized by us as such; consequently, we can apparently say that we are aware of their sequence. But such a crude way of reasoning cannot be called philosophical, because between the sequence in the change of states of our consciousness and the awareness of their sequence lies the same wide abyss as between any other object and subject of cognition. The sequence of sensations in itself is not yet the sensation of sequence. If, on the other hand, a sense of their sequence is added to successive sensations, then such a fact must be considered as some additional psychic phenomenon that requires a special explanation, more satisfactory than the above superficial identification of the sequence of sensations with its awareness.

In modern time units, the periods of the Earth's revolution around its axis and around the Sun, as well as the periods of the Moon's revolution around the Earth, are taken as a basis.

This is due to both historical and practical considerations. people need to coordinate their activities with the change of day and night or seasons.

Historically, the main unit for measuring short time intervals has been day (or day), reckoned by the minimum complete cycles of solar illumination change (day and night). As a result of dividing the day into smaller time intervals of the same length, clock, minutes and seconds... The day was divided into two equal consecutive intervals (conventionally day and night). Each of them was divided by 12 hours... Each hour divided by 60 minutes... Every minute - 60 seconds.

Thus, in hour 3600 seconds; in days 24 hours = 1440 minutes = 86 400 seconds.

Second became the main unit of time measurement in the International System of Units (SI) and the CGS system.

There are two systems for indicating the time of day:

French - the division of the day into two intervals of 12 hours (day and night) is not taken into account, but it is considered that the day is directly divided into 24 hours. The hour number can be from 0 to 23 inclusive.

English - this division is taken into account. The hours indicate from the beginning of the current half-day, and after the numbers they write the alphabetic index of the half-day. The first half of the day (night, morning) is designated AM, the second (day, evening) - PM from lat. Ante Meridiem / Post Meridiem (AM / PM). The hour number in 12-hour systems is written differently in different traditions: from 0 to 11 or 12.

Midnight is taken as the beginning of the countdown. Thus, midnight is 00:00 in French and 12:00 AM in English. Noon - 12:00 (12:00 PM). The time after 19 hours and another 14 minutes from midnight is 19:14 (7:14 PM in English).

On the dials of most modern watches (with hands), it is the English system that is used. However, such analogue watches are also produced where the French 24-hour system is used. Such clocks are used in those areas where it is difficult to judge the day and night (for example, on submarines or beyond the Arctic Circle, where there is a polar night and a polar day).

The duration of an average solar day is variable. And although it changes very little (it increases as a result of tides due to the action of the gravity of the Moon and the Sun on average by 0.0023 seconds per century over the past 2000 years, and over the last 100 years by only 0.0014 seconds), this is enough for significant distortion of the duration of a second, if we count 1/86 400 of the duration of a solar day as a second. Therefore, from the definition “hour - 1/24 day; minute - 1/60 hour; second - 1/60 minute "passed to the definition of the second as the basic unit, based on a periodic intra-atomic process not associated with any movements of celestial bodies (it is sometimes referred to as the SI second or" atomic second "when, in the context of its can be confused with the second determined from astronomical observations).

Time is a continuous value used to indicate the sequence of events in the past, present and future. Time is also used to determine the interval between events and to quantitatively compare processes occurring at different rates or frequencies. To measure time, any periodic sequence of events is used, which is recognized as the standard of a certain period of time.

The time unit in the International System of Units (SI) is second (c), which is defined as 9 192 631 770 periods of radiation corresponding to the transition between two hyperfine levels of the quantum state of the atom of cesium-133 at rest at 0 K. ).

The contraction of the heart muscle of a healthy person lasts one second. In one second, the Earth, revolving around the sun, covers a distance of 30 kilometers. During this time, our star itself manages to cover a path of 274 kilometers, rushing through the galaxy at great speed. The moonlight will not have time to reach the Earth during this time interval.

Millisecond (ms) - a unit of time, a fraction of a second (thousandth seconds).

The shortest exposure time in a conventional camera. The fly flaps its wings once every three milliseconds. Bee - once every five milliseconds. Every year the moon orbits the Earth two milliseconds slower as its orbit gradually expands.

Microsecond (μs) - a unit of time, a fraction of a second (ppm seconds).

Example: A flash with an air gap for capturing fast-moving events is capable of emitting a pulse of light shorter than one microsecond. It is used for shooting objects moving at very high speed (bullets, exploding balloons).

Nanosecond (ns) - a unit of time, a fraction of a second (billionth seconds).

Picosecond (ps) - a unit of time, a fraction of a second (one thousandth of a billionth seconds).

In one picosecond, light travels approximately 0.3 mm in vacuum. The fastest transistors operate in a time frame measured in picoseconds. Quarks, rare subatomic particles produced in powerful accelerators, have a lifetime of only one picosecond. The average duration of a hydrogenic bond between water molecules at room temperature is three picoseconds.

Femtosecond (fs) is a sub-multiple of a second (one millionth of a billionth seconds).

Pulsed titanium-sapphire lasers are capable of generating ultra-short pulses with a duration of only 10 femtoseconds. During this time, the light travels only 3 micrometers. This distance is comparable to the size of red blood cells (6-8 microns). An atom in a molecule makes one vibration in a time from 10 to 100 femtoseconds. Even the fastest chemical reaction takes place over a period of several hundred femtoseconds. The interaction of light with the pigments of the retina of the eye, and it is this process that allows us to see the environment, lasts about 200 femtoseconds.

Attosecond (ac) is a sub-multiple of a second (one billionth of a billionth seconds).

In one attosecond, light travels a distance equal to the diameter of three hydrogen atoms. The fastest processes that scientists are able to timed are measured in attoseconds. With the help of the most advanced laser systems, the researchers were able to obtain pulses of light lasting only 250 attoseconds. But no matter how infinitely small these time intervals may seem, they seem to be an eternity in comparison with the so-called Planck time (about 10-43 seconds), according to modern science, the shortest of all possible time intervals.

Minute (min) is an off-system unit of time measurement. A minute is equal to 1/60 of an hour or 60 seconds.

Hour (h) - off-system unit of time measurement. An hour is equal to 60 minutes or 3600 seconds.

Day (day) - off-system unit of time measurement equal to 24 hours. Usually, days mean a solar day, that is, a period of time during which the Earth makes one turn around its axis relative to the center of the Sun. A day consists of day, evening, night and morning.

Units are used to measure longer time intervals year, month and a weekconsisting of a whole number of solar days. Year approximately equal to the period of the Earth's revolution around the Sun (approximately 365.25 days), month - the period of the complete change of the phases of the moon (called the synodic month, equal to 29.53 days).

A week - off-system unit of time measurement. Usually a week is seven days. A week is a standard period of time used in most parts of the world to organize cycles of work and rest days.

Month - off-system unit of time measurement associated with the rotation of the moon around the earth.

Synodic month (from ancient Greek σύνοδος "conjunction, approach [with the Sun]") - the time interval between two consecutive identical phases of the moon (for example, new moons). The synodic month is the period of the phases of the moon, since the appearance of the moon depends on the position of the moon relative to the sun for an observer on Earth. The synodic month is used to calculate the timing of solar eclipses.

The most common Gregorian, as well as the Julian calendar, is based on year equal to 365 days. Since the tropical year is not equal to the whole number of solar days (365.2422), leap years, 366 days long, are used to synchronize the calendar seasons with the astronomical ones. The year is divided into twelve calendar months of varying duration (from 28 to 31 days). Usually, there is one full moon for each calendar month, but since the phases of the moon change slightly faster than 12 times a year, sometimes there are also the second full moons of the month, called the blue moon.

In the Hebrew calendar, the basis is the lunar synodic month and the tropical year, while the year can contain 12 or 13 lunar months. In the long run, the same months of the calendar fall at approximately the same time.

In the Islamic calendar, the basis is the lunar synodic month, and the year always contains strictly 12 lunar months, that is, about 354 days, which is 11 days less than the tropical year. Thanks to this, the beginning of the year and all Muslim holidays each year are shifted relative to the climatic seasons and the equinoxes.

Year (d) is a non-systemic unit of time equal to the period of the Earth's revolution around the Sun. In astronomy, the Julian year is a unit of time, defined as 365.25 days of 86,400 seconds each.

The Earth makes one revolution around the Sun and turns around its axis 365.26 times, the average level of the world's oceans rises by 1 to 2.5 millimeters. It will take 4.3 years for light from the nearest star, Proxima Centauri, to reach Earth. It will take roughly the same amount of time for surface ocean currents to circle the globe.

Julian year (a) is a unit of time, defined in astronomy as 365.25 Julian days of 86,400 seconds each. This is the average length of the year in the Julian calendar used in Europe in antiquity and the Middle Ages.

Leap year - a year in the Julian and Gregorian calendars, the duration of which is 366 days. That is, this year contains one day more days than a regular, non-leap year.

Tropical year , also known as the solar year, is the length of time it takes for the sun to complete one cycle of the seasons, as seen from Earth.

Sidereal period, also sidereal year (Latin sidus - star) - the period of time during which the Earth makes a complete revolution around the Sun relative to the stars. At noon on January 1, 2000, the sidereal year was 365.25636 days. This is approximately 20 minutes longer than the average tropical year on the same day.

Sidereal day - the period of time during which the Earth makes one complete revolution around its axis relative to the vernal equinox. A sidereal day for the Earth is 23 hours 56 minutes 4.09 seconds.

Sidereal time, also sidereal time - time measured relative to the stars, as opposed to time measured relative to the sun (solar time). Sidereal time is used by astronomers to determine where to point the telescope to see the desired object.

Fortnight - a unit of time equal to two weeks, that is, 14 days (or more precisely, 14 nights). The unit is widely used in the UK and some Commonwealth countries, but rarely in North America. In the Canadian and American pay systems, the term “bi-weekly” is used to describe the respective pay period.

Decade - a period of time including ten years.

Century, century - an off-system unit of time equal to 100 consecutive years.

During this time, the Moon will move away from the Earth by another 3.8 meters. Modern CDs and CDs will be hopelessly outdated by that time. Only one in every baby kangaroo can live to be a hundred years old, but a giant sea turtle can live for 177 years. The most modern CD can last over 200 years.

Millennium (also millennium) is a non-systemic unit of time equal to 1000 years.

Megagod (notation Myr) is a multiple of the year unit of time equal to one million (1,000,000 \u003d 10 6) years.

Gigagod (notation Gyr) - a similar unit equal to a billion (1,000,000,000 \u003d 10 9) years. It is used mainly in cosmology, as well as in geology and sciences related to the study of the history of the Earth. So, for example, the age of the Universe is estimated at 13.72 ± 0.12 thousand megalets or, which is the same, at 13.72 ± 0.12 gigalets.

In 1 million years, a spaceship traveling at the speed of light will not cover even half the way to the Andromeda galaxy (it is located at a distance of 2.3 million light years from Earth). The most massive stars, blue supergiants (they are millions of times brighter than the Sun) burn out during about this time. Due to the shifts of the tectonic layers of the Earth, North America will move away from Europe by about 30 kilometers.

1 billion years. It took approximately that long for our Earth to cool down after its formation. For oceans to appear on it, single-celled life arose and instead of an atmosphere rich in carbon dioxide, an atmosphere rich in oxygen would be established. During this time, the Sun passed four times in its orbit around the center of the Galaxy.

Planck time (tP) is a time unit in the Planck system of units. The physical meaning of this quantity is the time during which a particle, moving at the speed of light, will overcome the Planck length equal to 1.616199 (97) · 10⁻³⁵ meters.

In astronomy and in a number of other fields, along with the SI second, is used ephemeris second , the definition of which is based on astronomical observations. Assuming that there are 365.242 198 781 25 days in a tropical year, and the day is assumed to be constant (the so-called ephemeris calculus), we get that 31 556 925.9747 seconds in a year. Then it is believed that a second is 1/31 556 925.9747 of a tropical year. The secular change in the duration of the tropical year forces us to tie this definition to a specific era; thus, this definition refers to the tropical year at the time 1900.0.

Sometimes there is one third equal to 1/60 of a second.

Unit decade , depending on the context, may refer to 10 days or (less commonly) 10 years.

Indict ( indiction ), used in the Roman Empire (since the time of Diocletian), later in Byzantium, ancient Bulgaria and Ancient Russia, is equal to 15 years.

The Olympiad in antiquity was used as a unit for measuring time and was equal to 4 years.

Saros - the period of recurrence of eclipses, equal to 18 years 11⅓ days and known to the ancient Babylonians. The calendar period of 3600 years was also called Saros; smaller periods were named neros (600 years) and sossos (60 years).

To date, the smallest experimentally observed time interval is on the order of an attosecond (10 −18 s), which corresponds to 10 26 Planck times. By analogy with the Planck length, a time interval less than the Planck time cannot be measured.

In Hinduism, the "day of Brahma" - kalpa - equal to 4.32 billion years. This unit entered the Guinness Book of Records as the largest time unit.

Popular about Einstein and SRT

And here's another look at the theory of relativity: one online store sells a watch that does not have a second hand. But the dial rotates at the same speed relative to the hour and minute. And the name of this watch contains the name of the famous physicist "Einstein".

Time interval relativity consists in the fact that the course of the clock depends on the movement of the observer. A moving clock lags behind a stationary one: if any phenomenon has a certain duration for a moving observer, then it seems longer for a stationary one. If the system moved at the speed of light, then the motion in it would seem to a motionless observer to be infinitely slowed down. This is the famous "clock paradox".

Example

If I simultaneously (for myself) click my fingers on the apart hands, then for me the time interval between the clicks is zero (it is assumed that I checked this by the Einstein method - the counter light signals came together in the middle of the distance between the pairs of clicking fingers). But then, for any observer moving "sideways" relative to me, the clicks will not be simultaneous. So, according to his countdown, my moment will become a kind of duration.

On the contrary, if he clicks his fingers on the apart hands and from his point of view the clicks are simultaneous, then for me they will be non-simultaneous. Therefore, I perceive its moment as duration.

Likewise, my "almost instant" - a very short duration - stretches out for a moving observer. And his "almost instant" stretches out for me. In a word, my time for him is slowing down, his time is slowing down for me.

True, in these examples it is not immediately clear that in all reference frames the direction of time is preserved - necessarily from the past to the future. But this is easy to prove, remembering the prohibition of superluminal speeds, which makes it impossible to move back in time.

One more example

Ella and Alla are astronauts. They fly on different missiles in opposite directions and sweep past each other. Girls love to look in the mirror. In addition, both girls are endowed with the superhuman ability to see and contemplate subtle rapid phenomena.

Ella sits in a rocket, examines her own reflection and reflects on the inexorable passage of time. There, in the mirror, she sees herself in the past. After all, the light from her face first reached the mirror, then reflected from it and returned back. This journey of light took time. This means that Ella sees herself not as she is now, but a little bit younger. For about three hundred millionth of a second - because the speed of light is 300,000 km / s, and the path from Ella's face to the mirror and back is about 1 meter. “Yes,” Ella thinks, “you can even see yourself only in the past!”

Alla, flying on an oncoming rocket, having caught up with Ella, greets her and is curious about what her friend is doing. Oh, she looks in the mirror! However, Alla, looking into Ella's mirror, comes to different conclusions. According to Alla's estimation, Ella is aging more slowly than according to Ella herself!

In fact, while the light from Ella's face reached the mirror, the mirror relative to Alla shifted - after all, the rocket was moving. On the return path of light, Alla noted the further displacement of the rocket.

This means that for Alla the light went back and forth not along one straight line, but along two different, non-coinciding ones. On the path "Ella - Mirror - Ella" the light went at an angle, described something similar to the letter "D". Therefore, from the point of view of Alla, he went a longer way than from the point of view of Ella. And the greater, the greater the relative velocity of the missiles.

Alla is not only an astronaut, but also a physicist. She knows: according to Einstein, the speed of light is always constant, in any frame of reference is the same, because does not depend on the speed of movement of the light source. Therefore, for both Alla and Ella the speed of light is 300,000 km / s. But if light can travel different paths at the same speed in different frames of reference, the only conclusion from this is that time flows in different frames of reference in different ways. From Alla's point of view, Ella's light has come a long way. This means that it took more time, otherwise the speed of light would not have remained unchanged. According to Alla's measurements, Ella's time flows more slowly than Ella's own measurements.

The last example

If an astronaut leaves the Earth at a speed that differs from the speed of light by one twenty thousandth, flies in a straight line for a year there (counted by his watch and according to the events of his life), and then returns back. According to the astronaut's watch, this journey takes 2 years.

Returning to Earth, he will find (according to the relativistic formula for time dilation) that the inhabitants of the Earth have aged 100 years (according to the earth's clock), i.e., they will meet another generation.

It must be remembered that during such a flight there are sections of uniform motion (the frame of reference will be inertial, and SRT is applicable), as well as sections of motion with acceleration (acceleration at the start, braking upon landing, turn - the reference system is non-inertial and SRT is inapplicable.

Relativistic time dilation formula:

- - [Ya.N. Luginsky, M.S.Fezi Zhilinskaya, Y.S.Kabirov. English Russian Dictionary of Electrical Engineering and Power Engineering, Moscow, 1999] Subjects of electrical engineering, basic concepts of EN lapse ...

time interval - - [L.G. Sumenko. The English Russian Dictionary of Information Technology. M .: GP TsNIIS, 2003.] Topics information technologies in general EN time span ...

time interval - laiko tarpas statusas T sritis Standartizacija ir metrologija apibrėžtis Laiko skirtumas tarp dviejų akimirkų. atitikmenys: angl. time interval vok. Zeitintervall, n rus. time interval, m; time span, m pranc. intervalle de temps, m ... Penkiakalbis aiškinamasis metrologijos terminų žodynas

time interval - laiko tarpas statusas T sritis fizika atitikmenys: angl. time interval vok. Zeitintervall, n rus. time interval, m; time span, m pranc. intervalle de temps, m ... Fizikos terminų žodynas

time interval - Syn: interval, time ... Thesaurus of Russian business vocabulary

time interval between oscillations - the time interval between impulses - [L.G.Sumenko. The English Russian Dictionary of Information Technology. M .: GP TsNIIS, 2003.] Topics information technologies in general Synonyms time interval between impulses EN resting time ... Technical translator's guide

time span from inspection to maintenance - - Topics Oil and Gas EN inspection maintenance interval ... Technical translator's guide

The time interval after which the known events return in the same order. In astronomy, it is used to mean the time of revolution of a planet or comet. In chronology, in comparison with the cycle, P. denotes a period of time more ... ... Encyclopedic Dictionary of F.A. Brockhaus and I.A. Efron

A WEEK, a period of time equal to 7 days. First introduced by dr. East (7 days of the week were identified with the 7 planets known at that time) ... encyclopedic Dictionary

Books

Astrology Tse zhi xue. The art of timing, Davydov M .. Ze zhi xue is an ancient art of timing, considered a traditional Chinese astrological practice, whose origins date back to the reign of the Han Dynasty (206 BC - ...
Astrology Jie Zhi Xue. The art of timing. Drawing up a map of Ba Tzu. Method of the 12 Heavenly Rulers. Timing for therapy, Davydov M. Tse zhi xue - the ancient art of timing, is considered a traditional Chinese astrological practice, the origins of which originate in the era of the Han dynasty (206 BC - ...

When people say that the moment is enough for them, they probably do not realize that they promise to be free in exactly 90 seconds. Indeed, in the Middle Ages, the term "moment" defined a period of time lasting 1 / 40th of an hour, or, as it was then customary to say, 1 / 10th of a point, which was 15 minutes. In other words, it counted 90 seconds. Over the years, the moment has lost its original meaning, but it is still used in everyday life to denote an indefinite but very short interval.

So why do we remember the moment, but forget about ghari, nuktemeron, or something even more exotic?

1. Atom

The word "atom" comes from the Greek term for "indivisible", and therefore is used in physics to define the smallest particle of matter. But in the old days this concept was applied in relation to the shortest period of time. A minute was thought to have 376 atoms, each one less than 1/6 of a second long (or 0.15957 seconds to be precise).

2. Ghari

What kind of instruments and devices were not invented in the Middle Ages to measure time! While the Europeans exploited the hourglass and sundial with might and main, the Indians used clepsydras - ghari. Several holes were made in a hemispherical bowl made of wood or metal, after which it was placed in a pool of water. The liquid, seeping through the slots, slowly filled the vessel until the weight completely submerged it to the bottom. The whole process took about 24 minutes, so this range was named after the device - ghari. At that time, it was believed that a day consists of 60 ghari.

3. Chandelier

A chandelier is a period lasting 5 years. The use of this term is rooted in antiquity: then the lustrum denoted a five-year period of time that completed the establishment of the property qualification of Roman citizens. When the amount of tax was determined, the countdown came to an end, and a solemn procession poured into the streets of the Eternal City. The ceremony ended with lustration (purification) - a pretentious sacrifice to the gods on the Champ de Mars, performed for the welfare of citizens.

4. Mileway

All that glitters is not gold. Whereas a light year, seemingly created to define a period, measures distance, a mileway, a mile-long path, is used to measure time. Although the term sounds like a unit of measure for distance, in the early Middle Ages it meant a stretch of 20 minutes. This is how much it takes a person to cover a mile-long route on average.

5. Nundine

The inhabitants of Ancient Rome worked seven days a week, tirelessly. On the eighth day, however, which was considered the ninth for them (the Romans referred to the last day of the previous period as well), they organized huge markets in the cities - nundins. The market day was named "novem" (in honor of November - the ninth month of the 10-month agricultural "Year of Romulus"), and the time interval between the two fairs was called Nundine.

6. Nuctemeron

Nuktemeron, a combination of two Greek words "nyks" (night) and "hemera" (day), is nothing more than an alternative designation for the day we are used to. Anything that is considered nuctemerone, accordingly, lasts less than 24 hours.

7. Item

In Medieval Europe, a point, also called a point, was used to represent a quarter of an hour.

8. Quadrant

And the point's neighbor by epoch, the quadrant, defined a quarter of a day - a period of 6 hours.

9. Fifteen

After the Norman conquest, the word "Quinzieme", translated from French as "fifteen", was borrowed by the British to determine the duty, which replenished the state treasury by 15 pence from every pound earned in the country. In the early 1400s, the term also acquired a religious context: it began to be used to indicate the day of an important church holiday and two full weeks following it. So Quinzieme turned into a 15 day period.

10. Scruple

The word "Scrupulus", translated from Latin as "small sharp pebble", previously served as a pharmaceutical unit of weight measurement equal to 1/24 ounce (about 1.3 grams). In the 17th century, the scruple, which became a symbol for a small volume, expanded its meaning. It came to be used to indicate 1/60 of a circle (minute), 1/60 of a minute (seconds) and 1/60 of a day (24 minutes). Now, having lost its former meaning, scruple has transformed into scrupulousness - attentiveness to trifles.

And some more time values:

1 attosecond (one billionth of a billionth of a second)

The fastest processes that scientists are able to timed are measured in attoseconds. With the help of the most sophisticated laser systems, the researchers were able to obtain pulses of light lasting only 250 attoseconds. But no matter how infinitely small these time intervals may seem, they seem to be an eternity in comparison with the so-called Planck time (about 10-43 seconds), according to modern science, the shortest of all possible time intervals.

1 femtosecond (one millionth of a billionth of a second)

An atom in a molecule makes one vibration in a time from 10 to 100 femtoseconds. Even the fastest chemical reaction takes place over a period of several hundred femtoseconds. The interaction of light with the pigments of the retina of the eye, and it is this process that allows us to see the environment, lasts about 200 femtoseconds.

1 picosecond (one thousandth of a billionth of a second)

The fastest transistors operate in a time frame measured in picoseconds. Quarks, rare subatomic particles produced in powerful accelerators, have a lifetime of only one picosecond. The average duration of a hydrogen bond between water molecules at room temperature is three picoseconds.

1 nanosecond (billionth of a second)

A ray of light passing through an airless space can cover a distance of only thirty centimeters during this time. A microprocessor in a personal computer takes two to four nanoseconds to execute one command, such as adding two numbers. Another rare subatomic particle, the K meson has a lifetime of 12 nanoseconds.

1 microsecond (millionth of a second)

During this time, a beam of light in a vacuum will cover a distance of 300 meters, the length of about three football fields. A sound wave at sea level is capable of covering a distance equal to only one third of a millimeter in the same period of time. It takes 23 microseconds for a stick of dynamite to explode, the fuse of which has burned out to the end.

1 millisecond (thousandth of a second)

The shortest exposure time in a conventional camera. The familiar fly flaps its wings once every three milliseconds. Bee - once every five milliseconds. Every year the moon orbits the Earth two milliseconds slower as its orbit gradually expands.

1/10 second

Blink an eye. This is what we will have time to do within the specified period. It takes just that long for the human ear to distinguish the echo from the original sound. The Voyager 1 spacecraft, heading out of the solar system, moves two kilometers from the sun during this time. In a tenth of a second, the hummingbird flaps its wings seven times.

1 second

The contraction of the heart muscle of a healthy person lasts exactly this time. In one second, the Earth, revolving around the sun, covers a distance of 30 kilometers. During this time, our star itself manages to cover a path of 274 kilometers, rushing through the galaxy at great speed. The moonlight will not have time to reach the Earth during this time interval.

1 minute

During this time, the brain of a newborn baby gains up to two milligrams in weight. The heart of a shrew manages to contract 1000 times. The average person can say 150 words or read 250 words during this time. Light from the sun reaches the Earth in eight minutes. When Mars is at its closest distance from Earth, sunlight bouncing off the surface of the Red Planet reaches us in less than four minutes.

1 hour

This is how long it takes for the reproducing cells to split in half. In one hour, 150 Zhigulis leave the assembly line of the Volga Automobile Plant. Light from Pluto, the most distant planet in the solar system, reaches Earth in five hours and twenty minutes.

1 day

For humans, this is perhaps the most natural time unit based on the rotation of the Earth. According to modern science, the length of the day is 23 hours 56 minutes and 4.1 seconds. The rotation of our planet is constantly slowing down due to lunar gravity and other reasons. The human heart makes about 100,000 contractions per day, the lungs inhale about 11,000 liters of air. During the same time, a blue whale calf gains 90 kg in weight.

1 year

The Earth makes one revolution around the sun and rotates around its axis 365.26 times, the average level of the world's oceans rises by 1 to 2.5 millimeters, and 45 federal elections are being held in Russia. It will take 4.3 years for light from the nearest star, Proxima Centauri, to reach Earth. It will take roughly the same amount of time for surface ocean currents to circle the globe.

1st century

During this time, the Moon will move away from the Earth by another 3.8 meters, but the giant sea turtle can live as much as 177 years. The most modern CD can last over 200 years.

1 million years

A spaceship traveling at the speed of light will not cover even half the way to the Andromeda galaxy (it is located at a distance of 2.3 million light years from Earth). The most massive stars, blue supergiants (they are millions of times brighter than the Sun) burn out during about this time. Due to the shifts of the tectonic layers of the Earth, North America will move away from Europe by about 30 kilometers.

1 billion years

It took approximately that long for our Earth to cool down after its formation. For oceans to appear on it, single-celled life arose and instead of an atmosphere rich in carbon dioxide, an atmosphere rich in oxygen would be established. During this time, the Sun passed four times in its orbit around the center of the Galaxy.

Since the universe has only existed for 12-14 billion years, time units exceeding a billion years are rarely used. However, scientists, experts in cosmology, believe that the universe will probably continue after the last star goes out (in a hundred trillion years) and the last black hole evaporates (in 10100 years). So the universe still has a much longer path to go than it has already gone.

And remember, we recently found out with you that it is possible

AND UNITS OF THEIR MEASUREMENT

Time is more complex than length and mass. In everyday life, time is what separates one event from another. In mathematics and physics, time is considered as a scalar quantity, because time intervals have properties similar to those of length, area, mass.

Time intervals can be compared. For example, a pedestrian will spend more time on the same path than a cyclist.

Time intervals can be added. Thus, a lecture at an institute lasts as long as two lessons at school.

Time spans are measured. But the process of measuring time is different from measuring length, area, or mass. To measure length, you can reuse the ruler by moving it from point to point. The time interval taken as a unit can be used only once. Therefore, the unit of time should be a regularly repeated process. Such a unit in the International System of Units is called second... Along with the second, other units of time are also used: minute, hour, day, year, week, month, century. Units such as year and day were taken from nature, and the hour, minute, second were invented by man.

Year - this is the time of the Earth's revolution around the Sun.

Day is the time of the Earth's revolution around its axis.

The year consists of approximately 365 days. But a year of human life is made up of a whole number of days. Therefore, instead of adding 6 hours to each year, they add a whole day to every fourth year. This year consists of 366 days and is called leap.

A week.In Ancient Russia, the week was called the week, and Sunday was called a weekly day (when there was no work) or simply a week, i.e. day of rest. The names of the next five days of the week indicate how many days have passed since Sunday. Monday is immediately after the week, Tuesday is the second day, Wednesday is the middle, the fourth and fifth days are respectively Thursday and Friday, Saturday is the end of the day.

Month - not a very specific unit of time, it can consist of thirty-one days, of thirty and twenty-eight, twenty-nine in leap years (days). But this unit of time has existed since ancient times and is associated with the movement of the Moon around the Earth. The Moon makes one revolution around the Earth in about 29.5 days, and in a year it makes about 12 revolutions. These data served as the basis for the creation of ancient calendars, and the result of their centuries-old improvement is the calendar that we still use today.

Since the Moon makes 12 revolutions around the Earth, people began to count more fully the number of revolutions (that is, 22) per year, that is, a year - 12 months.

The modern division of the day into 24 hours also dates back to ancient times; it was introduced in Ancient Egypt. The minute and second appeared in Ancient Babylon, and in the fact that there are 60 minutes in an hour and 60 seconds in a minute, the influence of the sixagesimal number system invented by Babylonian scientists is reflected.

Time is the most difficult quantity to study. Temporary representations in children develop slowly in the course of long-term observations, the accumulation of life experience, and the study of other quantities.

First-graders' temporary ideas are formed primarily in the process of their practical (educational) activities: the daily routine, keeping the calendar of nature, the perception of the sequence of events when reading fairy tales, stories, when watching movies, daily writing in notebooks of the date of work - all this helps the child to see and realize time changes, feel the passage of time.

Time units that children get to know in elementary school: week, month, year, century, day, hour, minute, second.

Beginning with 1st class, it is necessary to start comparing the familiar time intervals often encountered in the experience of children. For instance, which lasts longer: lesson or break, school term or winter break; which is shorter: a student's school day or a parent's work day?

Such tasks contribute to the development of a sense of time. In the process of solving problems related to the concept of difference, children begin to compare the age of people and gradually master important concepts: older - younger - the same age. For instance:

“The sister is 7 years old, and the brother is 2 years older than the sister. How old is your brother?"

“Misha is 10 years old, and his sister is 3 years younger than him. How old is your sister?"

“Sveta is 7 years old, and her brother is 9 years old. How old will each of them be in 3 years? "

In 2nd grade children form more specific ideas about these time intervals. (2 cl. " Hour. Minute " from. 20)

For this purpose, the teacher uses a dial model with movable hands; explains that the big hand is called the minute, the small hand is called the hour, explains that all clocks are arranged in such a way that while the big hand moves from one small division to another, it passes 1 min, and while the small arrow moves from one large division to another, passes 1 hour... Time is counted from midnight to noon (12 noon) and from noon to midnight. Then exercises are suggested using the clock model:

♦ name the designated time (p. 20 # 1, p. 22 # 5, p. 107 # 12)

♦ designate the time that the teacher or students say.

Different forms of reading the clock readings are given:

9 h 30 min, 30 min of the tenth, half of the tenth;

4 hours 45 minutes, 45 minutes past five, 15 minutes to five, a quarter to five.

The study of the unit of time is used in solving problems (p. 21 №1).

IN 3rd grade clarifies children's ideas about such units of time as year, month, week ... (3 cl. H. 1, p. 9) For this purpose, the teacher uses the report card calendar. On it, children write out the names of the months in order and the number of days in each month. Months of the same length are immediately highlighted, the shortest month of the year (February) is marked. According to the calendar, students determine the ordinal number of the month:

♦ What is the name of the fifth month of the year?

♦ Which month is July?

The day of the week is set, if known, the day and month, and vice versa, it is established on which days of the month certain days of the week fall:

♦ What dates are Sundays in November?

Using the calendar, students solve tasks to find the duration of an event:

♦ How many days does autumn last? How many weeks does it last?

♦ How many days does spring break last?

Concepts about days is revealed through the concepts close to children about the parts of the day - morning, afternoon, evening, night. In addition, they rely on representations of the time sequence: yesterday, today, tomorrow. (Class 3, h. 1, p. 92 "Day")

Children are asked to list what they have been doing from yesterday morning until this morning, what they will do from tonight until tomorrow night, etc.

“Such periods of time are called days»

The ratio is set: Day \u003d 24 hours

Then a connection is established with the studied units of time:

♦ How many hours are there in 2 days?

♦ How many days in two weeks? At 4 weeks old?

♦ Compare: 1 week. * 8 days,25 hours * 1 day, 1 month * 35 days

Later, a time unit such as quarter (every 3 months, 4 quarters in total).

After getting acquainted with the shares, the following tasks are solved:

♦ How many minutes is a third of an hour?

♦ How many hours are the fourth of a day?

♦ What part of the year is one quarter?

IN 4th grade the ideas about the units of time already studied are refined (part 1, p. 59): a new relation is introduced -

1 year \u003d 365 or 366 days

Children will learn that the basic units of measurement are day - the time during which the Earth makes a complete revolution around its axis, and year - the time during which the Earth makes a complete revolution around the Sun.

Theme " Time from 0 hours to 24 hours "(S. 60). Children are introduced to the 24-hour reckoning. They learn that the beginning of the day is midnight (0 o'clock), that the hours during the day are counted from the beginning of the day, therefore after noon (12 o'clock) each hour has a different serial number (1 o'clock in the afternoon is 13 o'clock, 2 o'clock day -14 h ...)

Exercise examples:

♦ How to say in another way what time it is:

1) if 16 hours, 20 hours, three quarters of an hour, 21 hours 40 minutes, 23 hours 45 minutes have passed since the beginning of the day;

2) if they said: a quarter past five, half past two, a quarter to seven.

Express:

a) in hours: 5 days, 10 days 12 hours, 120 minutes

b) per day: 48 hours, 2 weeks

c) in months: 3 years, 8 years and 4 months, a quarter of a year

d) in years: 24 months, 60 months, 84 months.

Consider the simplest cases of addition and subtraction of values \u200b\u200bexpressed in units of time. The necessary conversions of units of time are performed here along the way, without first replacing the given values. To prevent errors in calculations, which are much more complicated than calculations with values \u200b\u200bexpressed in units of length and mass, it is recommended to give calculations in comparison:

30min 45sec - 20min 58sec;

30m 45cm - 20m 58cm;

30ts 45kg - 20ts 58kg;

♦ What action can be used to find out:

1) what time will the clock show in 4 hours, if it is now 0 hours, 5 hours ...

2) how long will it take from 14 hours to 20 hours, from 1 hour to 6 hours

3) what time did the clock show 7 hours ago, if it is now 13 hours, 7 hours 25 minutes?

1 min \u003d 60 s

Then the largest of the considered units of time is considered - the century, the ratio is established:

Examples of exercises:

♦ How old in 3 centuries? In the 10th century? In the 19th century?

♦ How many centuries are 600 years? 1100 years old? 2000 years?

♦ A.S. Pushkin was born in 1799 and died in 1837. In what century was he born and in what did he die?

Assimilation of relationships between units of time helps measure table , which should be hung in the classroom for a while, as well as systematic exercises in converting values \u200b\u200bexpressed in units of time, comparing them, finding different fractions of any unit of time, solving problems for calculating time.

1 c. \u003d 100 in a year 365 or 366 days

1 year \u003d 12 months in a month 30 or 31 days

1 day \u003d 24 hours (in February 28 or 29 days)

1 h \u003d 60 min

1 min \u003d 60 s

In the topic “ Adding and subtracting quantities "The simplest cases of addition and subtraction of composite named numbers, expressed in units of time, are considered:

♦ 18h 36 min -9h

♦ 20 min 30 s + 25 s

♦ 18h 36 min - 9 min (in a line)

♦ 5 h 48 min + 35 min

♦ 2 h 30 min - 55 min

Cases of multiplication are considered later:

♦ 2 min 30 s 5

For the development of temporal representations, the solution of problems is used to calculate the duration of events, its beginning and end.

The simplest tasks for calculating time within a year (month) are solved using a calendar, and within a day - using a clock model.

Exercise number 1

Children are invited to listen to two tape recordings. And one of them is 20 seconds, and the other is 15 seconds. After listening, the children should determine which of the proposed recordings lasts longer than the other. This task causes certain difficulties, the opinions of children differ.

Then the teacher finds out that in order to find out the duration of the melodies, they need to be measured. Questions:

Which of the two tunes lasts longer?

Can this be determined by ear?

What is needed for that. to determine the duration of the melodies.

In this lesson, you can enter hours and time unit - minute .

Exercise number 2

Children are invited to listen to two tunes. One of them lasts 1 minute and the other 55 seconds. After listening, children should determine which melody lasts longer. This task is difficult, the opinions of the children differ.

Then the teacher suggests counting how many times the arrow will move while listening to the melody. In the process of this work, children find out that when listening to the first melody, the arrow moved 60 times and went a full circle, i.e. the melody lasted one minute. The second melody lasted less because while it sounded the arrow moved 55 times. After that, the teacher informs the children that each "step" of the arrow is a period of time, which is called second ... The arrow, going through a full circle - a minute - makes 60 "steps, i.e. in one minute 60 seconds.

Children are offered a poster: “We invite all school students to a lecture on the rules of behavior on the water. The lecture lasts 60 ..... ".

The teacher explains that the artist who drew the poster did not know the units of time and did not write how long the lecture would last. The first grade students decided that the lecture would be 60 seconds long. one minute, and the second grade students decided that the lecture would last 60 minutes. Which one do you think is right? Students find out that second grade students are right. In the process of solving this problem, children conclude that when measuring intervals of time, it is necessary to use a single small one. In this lesson, a new time unit is introduced - hour .

Why did you decide the second grade students were right?

What is needed to avoid such errors?

How many minutes are in one hour? how many seconds?

Popular about Einstein and SRT

Example

One more example

The last example

Relativistic time dilation formula:

Our whole life is connected with time and is regulated by the periodic change of day and night, as well as the seasons. You know that the Sun always illuminates only half of the globe: in one hemisphere it is day, and in the other at this time it is night. Therefore, on our planet there are always points where it is at noon at the moment, and the Sun is in the upper climax, and there is midnight, when the Sun is in the lower climax.

The moment of the upper culmination of the center of the Sun is called true noon, the moment of the lower climax - true midnight... And the time interval between two successive culminations of the same name of the center of the Sun is called true sunny days.

It would seem that they can be used for accurate timing. However, due to the elliptical orbit of the Earth, solar days periodically change their duration. So, when the Earth is closest to the Sun, it orbits at about 30.3 km / s. And six months later, the Earth is at the farthest point from the Sun, where its speed drops by 1 km / s. This uneven movement of the Earth in its orbit causes an uneven apparent movement of the Sun across the celestial sphere. In other words, at different times of the year the Sun "moves" across the sky at different speeds. Therefore, the duration of true solar days is constantly changing and it is inconvenient to use them as a unit for measuring time. In this regard, in everyday life, not true, but average solar day, the duration of which is assumed constant and equal to 24 hours. Each hour of average solar time, in turn, is divided by 60 minutes, and each minute - by 60 seconds.

The measurement of time by solar days is associated with the geographic meridian. The time measured on a given meridian is called it local time, and it is the same for all items located on it. Moreover, the more east the earth's meridian is, the earlier the day begins on it. If we take into account that for every hour our planet rotates around its axis by 15 °, then the difference in time of two points in one hour corresponds to a difference in longitudes of 15 °. Consequently, the local time at two points will differ exactly as much as their geographical longitude, expressed in hourly measure, differs:

T 1 – T 2 = λ 1 - λ 2.

From the course in geography, you know that the initial (or, as it is also called, zero) meridian is taken as the meridian passing through the Greenwich Observatory, located near London. The local solar mean time of the Greenwich meridian is called universal time - Universal Time (abbreviated UT).

Knowing the universal time and geographic longitude of a point, you can easily determine its local time:

T 1 = UT + λ 1 .

This formula also allows you to find geographic longitude using universal time and local time, which is determined from astronomical observations.

However, if in everyday life we \u200b\u200bused the local time, then as we move between settlements located to the east or west of our permanent place of residence, we would have to continuously move the clock hands.

For example, let's determine how much later it is noon in St. Petersburg compared to Moscow, if their geographic longitude is known in advance.

In other words, in St. Petersburg, noon will come about 29 minutes 12 seconds later than in Moscow.

The resulting inconveniences are so obvious that at present, almost the entire population of the world uses belt counting system... It was proposed by the US teacher Charles Dowd in 1872 for use on the railways of America. And already in 1884, the International Meridian Conference was held in Washington, the result of which was the recommendation to use Greenwich time as universal time.

According to this system, the entire globe is divided into 24 time zones, each of which extends 15 ° in longitude (or one hour). The Greenwich meridian time zone is considered to be zero. The rest of the belts in the direction from zero to the east are assigned numbers from 1 to 23. Within one belt at all points at each moment the standard time is the same, and in neighboring belts it differs by exactly one hour.

Thus, the standard time, which is accepted in a particular place, differs from the universal time by the number of hours equal to the number of its time zone:

T = UT + n .

If you look at the map of time zones, it is not difficult to see that their borders coincide with the meridians only in sparsely populated places, on the seas and oceans. In other places, the boundaries of the belts, for greater convenience, are drawn along state and administrative boundaries, mountain ranges, rivers and other natural boundaries.

Also, from pole to pole, a conditional line runs along the surface of the globe, on different sides of which the local time differs by almost a day. This line was named date lines.It passes approximately 180 degrees along the meridian.

Currently, it is considered a more reliable and convenient time atomic time, which was introduced by the International Committee for Weights and Measures in 1964. And the atomic clock was taken as the standard of time, the error of which is approximately one second in 50 thousand years. Therefore, since January 1, 1972, the countries of the world have been keeping track of time according to them.

For counting long periods of time, in which a certain length of months is established, their order in the year and the initial moment of counting years, was introduced the calendar.It is based on periodic astronomical phenomena: rotation of the Earth around its axis, change in lunar phases, rotation of the Earth around the Sun. Moreover, any calendar system (and there are more than 200 of them) is based on three main units of time measurement: the average solar day, the synodic month, and the tropical (or solar) year.

Recall that synodic month is the time interval between two consecutive identical phases of the moon. It is approximately equal to 29.5 days.

AND tropical year- This is the time interval between two successive passages of the center of the Sun through the vernal equinox. Its average duration since January 1, 2000 is 365 days 05 hours 48 minutes 45.19 seconds.

As you can see, the synodic month and tropical year do not contain a whole number of average solar days. Therefore, many peoples in their own way tried to agree on the day, month and year. This, subsequently, led to the fact that at different times different peoples had their own calendar system. However, all calendars can be roughly divided into three types: lunar, lunisolar and solar.

IN lunar calendar the year is divided into 12 lunar months, which alternately contain 30 or 29 days. As a result, the lunar calendar is shorter than the solar year by about ten days. Such a calendar has become widespread in the modern Islamic world.

Lunar-solar calendars the most difficult. They are based on the ratio that 19 solar years are equal to 235 lunar months. As a consequence, there are 12 or 13 months in a year. At present, such a system has been preserved in the Hebrew calendar.

IN solar calendar the duration of the tropical year is taken as a basis. One of the first solar calendars is considered to be the ancient Egyptian calendar, created around the 5th millennium BC. In it, the year was divided into 12 months, 30 days each. And at the end of the year 5 more holidays were added.

The immediate predecessor of the modern calendar was the calendar developed on January 1, 45 BC in Ancient Rome by the order of Julius Caesar (hence its name - julian).

But the Julian calendar was not perfect either, since the length of the calendar year in it differed from the tropical year by 11 minutes and 14 seconds. It would seem that nothing at all. But by the middle of the 16th century, a shift in the day of the vernal equinox, associated with church holidays, by 10 days was noticed.

To compensate for the accumulated error and avoid such a shift in the future, in 1582 Pope Gregory XIII carried out a calendar reform that moved the counting of days by 10 days ahead.

At the same time, in order for the average calendar year to better correspond to the solar year, Gregory XIII changed the rule of leap years. The year remained a leap year, the number of which was a multiple of four, but an exception was made for those that were multiples of one hundred. Such years were leap years only when they were also divisible by 400. For example, 1700, 1800 and 1900 were simple years. But 1600 and 2000 are leap years.

The revised calendar is named gregorian calendar or new style calendar.

In Russia, the new style was introduced only in 1918. By this time, a difference of 13 days had accumulated between him and the old style.

However, the old calendar is still alive in the memory of many people. It is thanks to him that the "old New Year" is celebrated in many countries of the former USSR on the night of January 13-14.

The main unit of time is sidereal day. This is the period of time during which the Earth makes a complete revolution around its axis. When determining the sidereal day, instead of the uniform rotation of the Earth, it is more convenient to consider the uniform rotation of the celestial sphere.

Sidereal days are called the time interval between two consecutive culminations of the same name of the point of Aries (or any star) on the same meridian. For the beginning of a sidereal day, the moment of the upper culmination of the Aries point is taken, that is, the moment when it passes through the noon part of the observer's meridian.

Due to the uniform rotation of the celestial sphere, the Aries point uniformly changes its hour angle by 360 °. Therefore, sidereal time can be expressed by the western hour angle of the point of Aries, that is, S \u003d f y / w.

The hour angle of the Aries point is expressed in degrees and in time. For this purpose, the following ratios are used: 24 h h \u003d \u003d 360 °; 1 m \u003d 15 °; 1 m \u003d 15 "; 1 s \u003d 0/2 5 and vice versa: 360 ° \u003d 24 h; 1 ° \u003d (1/15) h \u003d 4 M; 1" \u003d (1/15) * \u003d 4 s; 0 ", 1 \u003d 0 s, 4.

Sidereal days are divided into even smaller units. Sidereal hour is equal to 1/24 of a sidereal day, sidereal minute - 1/60 of a sidereal hour and sidereal second - 1/60 of a sidereal minute.

Hence, sidereal time call the number of sidereal hours, minutes and seconds elapsed from the beginning of a sidereal day to a given physical moment.

Sidereal time is widely used by astronomers when observing at observatories. But this time is inconvenient for the everyday life of a person, which is associated with the diurnal movement of the Sun.

The daily movement of the Sun can be used to count the time in true solar days. True sunny days is called the time interval between two successive culminations of the same name of the Sun on the same meridian. For the beginning of a true solar day, the moment of the upper culmination of the true Sun is taken. From here you can get the true hour, minute and second.

The big disadvantage of sunny days is that their duration is variable throughout the year. Instead of true solar days, the average solar day is taken, which are the same in magnitude and equal to the annual average value of true solar days. The word "sunny" is often omitted and they simply say - average day.

To introduce the concept of an average day, an auxiliary fictitious point is used that moves uniformly along the equator and is called the average equatorial sun. Its position on the celestial sphere is predicted by the methods of celestial mechanics.

The hour angle of the average sun changes uniformly, and therefore the average day is the same in magnitude throughout the year. Having an idea of \u200b\u200bthe average sun, we can give a different definition of the average day. Average days is called the time interval between two successive culminations of the same name of the middle sun on the same meridian. The beginning of the middle day is taken as the moment of the lower climax of the middle sun.

The average day is divided into 24 parts - the average hour is obtained. The average hour is divided by 60, the average minute is obtained and, accordingly, the average second. In this way, average time call the number of average hours, minutes and seconds elapsed from the beginning of the average day to a given physical moment. Average time is measured by the western hour angle of the average sun. The average day is 3 M 55 s longer than the star day, 9 average time units. Therefore, sidereal time goes forward by about 4 minutes every day. In one month, sidereal time will go by 2 hours in comparison with the average, and so on. In a year, sidereal time will go forward by one day. Consequently, the beginning of a sidereal day during the year will fall on different times of the average day.

In navigational aids and astronomy literature, the expression "civil mean time", or more often "mean (civil) time" is often found. This is explained as follows. Until 1925, the beginning of the average day was taken as the moment of the upper climax of the average sun, therefore, the average time was reckoned from the average noon. This time was used by astronomers when observing, so as not to divide the night into two dates. In civilian life, the same average time was used, but the average midnight was taken as the beginning of the average day. These average days were called civil average days. The average time, counted from midnight, was called civil average time.

In 1925, according to the International Agreement, astronomers adopted civil mean time for their work. Consequently, the concept of average time, measured from the average half day, has lost its meaning. There is only civil average time, which is simplistically called the average time.

If we denote by T - the average (civil) time, and in-hour angle of the average sun, then T \u003d t + 12 H.

Of particular importance is the connection between sidereal time, the hour angle of a star and its right ascension. This relationship is called the main sidereal time formula and is written as follows:

The obviousness of the basic formula of time follows from Fig. 86. At the moment of the upper culmination t-0 °. Then S - a. For the lower climax 5 \u003d 12 H -4 + a.

The basic time formula can be used to calculate the hour angle of the star. Indeed: r \u003d S + 360 ° -a; denote 360 \u200b\u200b° - a \u003d m. Then

The magnitude of t is called the stellar complement, and it is given in the Marine Astronomical Yearbook. Sidereal time S is calculated at a given moment.

All times we obtained were counted from an arbitrarily chosen observer meridian. Therefore they are called local times. So, local time is called the time on a given meridian. Obviously, at the same physical moment, the local times of different meridians will not be equal. This also applies to the hour corners. The hour angles measured from an arbitrary meridian of the observer are called local hour angles, the latter are not equal to each other.

Let's find out the relationship between homogeneous local times and local hour angles of the stars on different meridians.

The celestial sphere in fig. 87 is projected on the equatorial plane; QZrpPn Q "-meridian of the observer passing through Greenwich Zrp-zenith of Greenwich.

Consider additionally two more points: one located to the east in longitude LoSt with the zenith Z1 and the other to the west in longitude Лw with zenith Z2. Draw the point of Aries y, the middle sun O and the luminary o.

Based on the definitions of times and hour angles, then

and
where S GR, T GR and t GR - respectively sidereal time, mean time and hour angle of the star on the Greenwich meridian; S 1 T 1 and t 1 - sidereal time, mean time and hour angle of the star on the meridian located east of Greenwich;

S 2, T 2 and t 2 - sidereal time, mean time and hour angle of the star on the meridian located to the west of Greenwich;

L - longitude.

Figure: 86.

Figure: 87.

Times and hour angles referred to any meridian, as mentioned above, are called local times and hour angles, then
Thus, homogeneous local times and local hour angles at any two points differ from each other by the difference in longitudes between them.

To compare times and hour angles at the same physical moment, the initial (zero) meridian passing through the Greenwich Observatory was taken. This meridian was named greenwich.

The times and hour angles referred to this meridian are called Greenwich times and Greenwich hour angles. Greenwich Mean (Civil) Time is called Universal Time (or World Time).

In the relationship between times and hour angles, it is important to remember that times and western hour angles to the east are always greater than those of Greenwich. This feature is a consequence of the fact that the rising, setting and culmination of the heavenly bodies on the meridians located to the east occur earlier than on the Greenwich meridian.

Thus, the local mean time at different points on the earth's surface will not be the same at the same physical moment. This leads to great inconvenience. To eliminate this, the entire globe was divided along the meridians into 24 belts. In each zone, the same so-called standard time is adopted, equal to the local average (civil) time of the central meridian. The central meridians are 0 meridians; fifteen; thirty; 45 °, etc. to the east and west. The boundaries of the belts run to one side and the other from the central meridian through 7 °, 5. The width of each belt is 15 °, and therefore, at the same physical moment, the time difference in two adjacent belts is 1 hour. The belts are numbered from 0 to 12 in the east and west sides. The belt, the central meridian of which passes through Greenwich, is considered to be the zero belt.

In reality, the boundaries of the belts do not pass strictly along the meridians, otherwise some districts, regions, and even cities would have to be divided. To eliminate this, borders sometimes go along the borders of states, republics, rivers, etc.

In this way, standard time they call the local, average (civil) time of the central meridian of the belt, taken the same for the entire belt. Zone time is designated TP. We introduced zone time in 1919. In 1957, due to changes in administrative regions, some changes were made to the previously existing zones.

The relationship between the time zone TP and the universal time (Greenwich) TGR is expressed by the following formula:

In addition (see formula 69)

Based on the last two expressions

After the First World War, in different countries, including the USSR, they began to move the hour hand 1 hour or more forward or backward. The translation was done for a certain period, mostly for the summer and by government order. This time began to be called daylight saving time T. D.

In the Soviet Union, since 1930, by the decree of the Council of People's Commissars, the hands of the clocks in all zones were moved forward 1 hour year-round. This was due to economic considerations. Thus, daylight saving time in the USSR differs from Greenwich time by the zone number plus 1 hour.

The life of the crew and the dead reckoning of the ship follow the ship's clock, which shows the ship's time T C. Ship time call the standard time of the time zone in which the ship's clock is set; it is recorded to the nearest 1 min.

When a vessel moves from one zone to another, the hands of the ship's clock are shifted 1 hour forward (if the transition is made to the eastern belt) or 1 hour backward (if to the western belt).

If, at the same physical moment, we move away from the zero belt and come to the twelfth belt from the eastern and western sides, then we will notice a discrepancy by one calendar date.

The 180 ° meridian is considered to be the date line (demarcation time line). If the ships cross this line in an easterly direction (that is, they are heading from 0 to 180 °), then at the first midnight they repeat the same date. If the ships cross it in a westerly direction (that is, they go on courses from 180 to 360 °), then at the first midnight one (last) date is omitted.

The demarcation line for the predominant part of its length coincides with the 180 ° meridian and deviates from it only in places, skirting the islands and capes.

The calendar is used to calculate large periods of time. The main difficulty in creating a solar calendar is the incommensurability of the tropical year (365, 2422 average days) by the whole number of average days. Currently, in the USSR and basically in all states, the Gregorian calendar is used. To equalize the length of the tropical and calendar (365, 25 average days) years in the Gregorian calendar, it is customary to consider every four years: three years are simple but 365 average days and one leap year - 366 average days.

Example 36. March 20, 1969 Zone time TP \u003d 04 H 27 M 17 C, 0; A \u003d 81 ° 55 ", 0 O st (5 H 27 M 40 C, 0 O st). Determine T gr and T M.

Around the Earth. This choice of units is due to both historical and practical considerations: the need to coordinate the activities of people with the change of day and night or seasons.

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"Time. Units of measurement of time "- Gordikova E.A.

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Subtitles

Day, hour, minute and second

Historically, the main unit for measuring short time intervals has been a day (often referred to as "day"), measured by the minimum complete cycles of solar illumination change (day and night).

As a result of dividing the day into smaller time intervals of the same length, hours, minutes and seconds arose. The origin of division is probably associated with the duodecimal number system, which was adhered to in ancient Sumer. The day was divided into two equal consecutive intervals (conditionally day and night). Each of them was divided by 12 hours ... Further division of the hour goes back to the sixagesimal number system. Every hour was divided by 60 minutes ... Every minute - by 60 seconds .

Thus, there are 3600 seconds in an hour; in a day - 24 hours, or 1440 minutes, or 86,400 seconds.

Hours, minutes and seconds have become part of our everyday life, they have become naturally perceived even against the background of the decimal number system. Now it is these units that are most often used to measure and express periods of time. Second (Russian designation: from; international: s) is one of the seven basic units in the International System of Units (SI) and one of the three basic units in the CGS system.

Units "minute" (Russian designation: min; international: min), "Hour" (Russian designation: h; international: h) and "day" (Russian designation: days; international: d) are not included in the SI system, but in the Russian Federation they are approved for use as off-system units without limiting the validity period of the admission with the scope of "all areas". In accordance with the requirements of the SI Brochure and GOST 8.417-2002, the name and designation of the time units “minute”, “hour” and “day” are not allowed to be used with sub-multiples and multiples of SI prefixes.

Astronomy uses the notation h, m, from (or h, m, s) in the superscript: for example, 13 h 20 m 10 s (or 13 h 20 m 10 s).

Use to indicate time of day

First of all, hours, minutes and seconds were introduced to facilitate the indication of time coordinates within a day.

A point on the time axis within a specific calendar day is indicated by an indication of the whole number of hours that have passed since the beginning of the day; then a whole number of minutes that have passed since the beginning of the current hour; then an integer number of seconds that have passed since the beginning of the current minute; if it is necessary to even more accurately indicate the time position, then the decimal system is used, indicating the past fraction of the current second (usually to hundredths or to thousandths) in decimal fraction.

Letter designations "h", "min", "s" are usually not written on the letter, but only numbers separated by a colon or a period are indicated. Minute and second number can range from 0 to 59 inclusive. If high precision is not required, the number of seconds is not indicated.

There are two systems for indicating the time of day. In the so-called French system, the division of the day into two intervals of 12 hours (day and night) is not taken into account, but it is believed that the day is directly divided into 24 hours. The hour number can be from 0 to 23 inclusive. In the "English system" this division is taken into account. The hours indicate from the beginning of the current half-day, and after the numbers they write the alphabetic index of the half-day. The first half of the day (night, morning) is designated AM, the second (day, evening) - PM; these designations come from lat. ante meridiem and post meridiem (before noon / afternoon). The hour number in 12-hour systems in different traditions is written in different ways: from 0 to 11 or 12, 1, 2,…, 11. Since all three temporary subcoordinates do not exceed one hundred, two digits are sufficient to write them in the decimal system; therefore, the values \u200b\u200bof hours, minutes and seconds are written in two-digit decimal numbers, adding a zero in front of the number, if necessary (in the English system, however, the hour number is written in one- or two-digit decimal numbers).

On the dials of most modern watches (with hands), it is the English system that is used. However, such analogue watches are also produced where the French 24-hour system is used. Such watches are used in those areas where it is difficult to judge the day and night (for example, on submarines or beyond the Arctic Circle, where there is a polar night and a polar day).

Use to indicate a time interval

Hours, minutes and seconds are not very convenient for measuring time intervals, since they do not use the decimal number system. Therefore, only seconds are usually used to measure time intervals.

However, sometimes the actual hours, minutes and seconds are used. So, the duration of 50,000 s can be written as 13 hours 53 minutes. 20 s.

Standardization

Starting from the SI second, the minute is defined as 60 seconds, the hour as 60 minutes, and the calendar (Julian) day as exactly 86,400 s. Currently, the Julian day is shorter than the average solar day by about 2 milliseconds; to eliminate the accumulating discrepancies, leap seconds are introduced. The Julian year is also defined (exactly 365.25 Julian days, or 31,557,600 s), sometimes called the scientific year.

In astronomy and in a number of other fields, along with the SI second, the ephemeris second is used, the definition of which is based on astronomical observations. Assuming that there are 365.24219878125 days in a tropical year, and a day assuming a constant duration (the so-called ephemeris calculus), we get that 31,556,925.9747 seconds in a year. The second is then considered to be 1 ⁄ 31,556,925.9747 of a tropical year. The secular change in the duration of the tropical year forces us to tie this definition to a specific era; thus, this definition refers to the tropical year at the time 1900.0.

Multiples and submultiples

The second is the only time unit with which SI prefixes are used to form sub-multiples and (rarely) multiples.

Year, month, week

For longer time intervals, the units of measure are year, month and week, which consist of a whole number of solar days. The year is approximately equal to the period of the Earth's revolution around the Sun (approximately 365.25 days), the month is the period of the complete change of the phases of the moon (called the synodic month, equal to 29.53 days).

In the most common Gregorian, as well as in the Julian calendar, a year equal to 365 days is taken as a basis. Since the tropical year is not equal to the whole number of solar days (365.2422), leap years, 366 days long, are used to synchronize the calendar seasons with the astronomical ones. The year is divided into twelve calendar months of varying duration (from 28 to 31 days). Usually, there is one full moon for each calendar month, but since the phases of the moon change slightly faster than 12 times a year, sometimes there are also the second full moons of the month, called the blue moon.

Century, millennium

Even larger units of time are a century (100 years) and a millennium (1000 years). A century is sometimes divided into decades. In sciences such as astronomy and geology, which study very long periods of time (millions and billions of years), even larger units of time are sometimes used - for example, gigagod (billion years).

Megagod and gigagod

Megagod (notation Myr) - a multiple of a year unit of time equal to a million years; gigagod (notation Gyr) - a similar unit equal to a billion years. These units are used primarily in cosmology, as well as in geology and sciences related to the study of the history of the Earth. So, for example, the age of the universe is estimated at 13.72 ± 0.12 gigalets. The established practice of using these units contradicts the "Regulations on the units of quantities allowed for use in the Russian Federation", according to which the unit of time year (just like, for example, a week, month, millennium) should not be used with multiples and sub-multiples.

Rare and obsolete units

In the UK and the Commonwealth of Nations, the unit of measurement for fortnight is two weeks.

November 2nd, 2017

So why do we remember the moment, but forget about ghari, nuktemeron, or something even more exotic?

1. Atom

2. Ghari

3. Chandelier

4. Mileway

5. Nundine

6. Nuctemeron

7. Item

In Medieval Europe, a point, also called a point, was used to represent a quarter of an hour.

8. Quadrant

And the point's neighbor by epoch, the quadrant, defined a quarter of a day - a period of 6 hours.

9. Fifteen

10. Scruple

And some more time values:

1 attosecond (one billionth of a billionth of a second)

1 femtosecond (one millionth of a billionth of a second)

1 picosecond (one thousandth of a billionth of a second)

1 nanosecond (billionth of a second)

1 microsecond (millionth of a second)

1 millisecond (thousandth of a second)

1/10 second

1 second

1 minute

1 hour

1 day

1 year

1st century

During this time, the Moon will move away from the Earth by another 3.8 meters, but the giant sea turtle can live as much as 177 years. The most modern CD can last over 200 years.

1 million years

1 billion years

sources
http://www.mywatch.ru/conditions/

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All human life is associated with time, and the need to measure it arose in ancient times.

The first natural unit of measure of time was the day, which regulated the work and rest of people. From the prehistoric era, the day was divided into two parts - day and night. Then morning (early afternoon), noon (midday), evening (late afternoon), and midnight (midnight) stood out. Even later, the day was divided into 24 equal parts, which were called "hour". To measure shorter time intervals, the hour began to be divided by 60 minutes, the minute - by 60 s, the second - into tenths, hundredths, thousandths, etc. of a second.

The periodic change of day and night occurs due to the rotation of the Earth around its axis. But we, being on the surface of the Earth and participating with it in this rotation, do not feel it and judge its rotation by the daily motion of the Sun, stars and other celestial bodies.

The time interval between two successive upper (or lower) culminations of the center of the Sun on the same geographic meridian, equal to the period of rotation of the Earth relative to the Sun, is called true solar days, and the time expressed in fractions of this day - hours, minutes and seconds - is called true solar time T 0.

The beginning of a true solar day is taken to be the moment of the lower culmination of the center of the Sun (true midnight), when T 0 \u003d 0 h. At the moment of the upper culmination of the Sun, at true noon, T 0 \u003d 12 h. At any other moment of the day, the true solar time T 0 \u003d 12h + t 0, where t 0 is the hour angle (see Celestial coordinates) of the center of the Sun, which can be determined when the Sun is above the horizon.

But it is inconvenient to measure the time with true solar days: during the year they periodically change their duration - in winter they are longer, in summer they are shorter. The longest true solar days are 51 s longer than the shortest. This happens because the Earth, in addition to rotating around its axis, moves in an elliptical orbit and around the Sun. The consequence of this movement of the Earth is the apparent annual movement of the Sun among the stars along the ecliptic, in the direction opposite to its daily movement, that is, from west to east.

The movement of the Earth in its orbit occurs at a variable speed. When the Earth is near perihelion, its speed of movement in orbit is highest, and when it passes near aphelion, its speed is lowest. The uneven movement of the Earth in its orbit, as well as the inclination of its axis of rotation to the plane of the orbit, are the reasons for the unevenness of the change in the right ascension of the Sun during the year, and, consequently, the inconstancy of the duration of the true solar day.

In order to eliminate this inconvenience, the concept of the so-called middle sun was introduced. This is an imaginary point that, during the year (for the same time as the real Sun along the ecliptic), makes one complete revolution along the celestial equator, while moving among the stars from west to east completely evenly and passing the vernal equinox simultaneously with the Sun. The time interval between two successive upper (or lower) climaxes of the average sun on the same geographic meridian is called the average solar days, and the time, expressed in their shares - hours, minutes and seconds - is the average solar time T cf. The duration of an average solar day is obviously equal to the average duration of a true solar day per year.

The beginning of the average solar day is taken as the moment of the lower climax of the average sun (average midnight). At this moment, T av \u003d 0 h. At the moment of the upper culmination of the middle sun (at average noon), the average solar time is T av \u003d 12 h, and at any other moment of the day T av \u003d 12 h + t av, where t av is the hour angle of the average sun.

The middle sun is an imaginary point unmarked in the sky, so it is impossible to determine the hour angle t cp directly from observations. But it can be calculated if the equation of time is known.

The equation of time is the difference between mean solar time and true solar time at the same moment, or the difference between the hour angles of the mean and true Sun, i.e.

η \u003d T av - T0 0 \u003d t av - t 0.

The equation of time can be calculated theoretically for any moment in time. It is usually published in astronomical yearbooks and calendars for midnight on the Greenwich meridian. The approximate value of the equation of time can be found from the attached graph.

The graph shows that 4 times a year the equation of time is equal to zero. This happens around April 15, June 14, September 1 and December 24. The equation of time reaches its greatest positive value around February 11 (η \u003d +14 min), and negative - around November 2 (η \u003d -16 min).

Knowing the equation of time and the true solar (from observations of the Sun) time for a given moment, you can find the average solar time. However, the average solar time is easier and more accurate to calculate from the sidereal time determined from observations.

The time interval between two successive upper (or lower) climaxes of the vernal equinox on the same geographic meridian is called sidereal days, and the time, expressed in their fractions - hours, minutes and seconds - sidereal time.

The moment of the upper climax of the vernal equinox point is taken as the beginning of a sidereal day. At this moment sidereal time s \u003d 0 h, and at the moment of the lower culmination of the vernal equinox 5 \u003d 12 h. At any other moment of sidereal day sidereal time s \u003d t γ, where t γ is the hour angle of the vernal equinox.

The vernal equinox point in the sky is not marked by anything, and it is impossible to find its hour angle from observations. Therefore, astronomers calculate sidereal time by determining the hour angle of the star t *, for which right ascension α is known; then s \u003d α + t *.

At the moment of the star's upper culmination, when t * \u003d 0, sidereal time s \u003d α; at the moment of the lower climax of the star t * \u003d 12 hours and s \u003d α + 12 hours (if a is less than 12 hours) or s \u003d α - 12 hours (if α is more than 12 hours).

Measuring time by sidereal days and their fractions (sidereal hours, minutes and seconds) is used in solving many astronomical problems.

Average solar time is determined using sidereal time based on the following ratio established by numerous observations:

365.2422 solar mean days \u003d 366.2422 sidereal days, whence it follows:

24 h sidereal time \u003d 23 h 56 min 4.091 s mean solar time;

24 hours mean solar time \u003d 24 hours 3 minutes 56.555 s sidereal time.

The measurement of time by sidereal and solar days is associated with the geographic meridian. The time measured on a given meridian is called the local time of this meridian, and it is the same for all points located on it. Due to the rotation of the Earth from west to east, local time at the same moment is different on different meridians. For example, on a meridian located 15 ° east of the given one, the local time will be 1 hour longer, and on a meridian located 15 ° to the west, it will be 1 hour less than on this meridian. The difference in local times of two points is equal to the difference in their longitudes, expressed in hourly measure.

According to the international agreement, the meridian passing through the former Greenwich Observatory in London was taken as the initial meridian for calculating geographic longitudes (now it has been transferred to another place, but the Greenwich meridian was left initial). The local solar mean time of the Greenwich meridian is called universal time. In astronomical calendars and yearbooks, the moments of most phenomena are indicated in universal time. The moments of these phenomena according to local time of any point are easy to determine, knowing the longitude of this point from Greenwich.

In everyday life, it is inconvenient to use local time, because there are in principle the same number of local time counting systems [as there are geographic meridians, that is, there are countless ones. The large difference between UTC and the local time of meridians, which are far from Greenwich Mean Time, creates inconveniences when using Universal Time in everyday life. So, for example, if it is noon in Greenwich, that is, 12 o'clock universal time, then in Yakutia and in Primorye in the Far East of our country it has already come late evening.

Since 1884, in many countries of the world, the belt system for calculating the mean solar time has been used. This time keeping system is based on dividing the Earth's surface into 24 time zones; at all points within one zone at each moment the zone time is the same, in neighboring zones it differs by exactly 1 hour. In the zone time system, 24 meridians spaced 15 ° from each other in longitude are taken as the main meridians of time zones. The boundaries of the belts in the seas and oceans, as well as in sparsely populated areas, are drawn along the meridians, which are 7.5 ° to the east and west of the main one. In the rest of the Earth, the boundaries of the belts, for greater convenience, are drawn along state and administrative boundaries, rivers, mountain ranges, etc. close to these meridians.

By international agreement, the meridian with a longitude of 0 ° (Greenwich) was taken as the initial one. The corresponding time zone is considered zero. The rest of the belts in the direction from zero to the east are assigned numbers from 1 to 23.

The zone time of a point is the local mean solar time of the main meridian of the time zone in which this point is located. The difference between the standard time in any time zone and the universal time (the time of the zero zone) is equal to the time zone number.

Timezone clocks in all time zones show the same number of seconds and minutes and differ only by an integer number of hours. The time zone system eliminates the inconvenience associated with using both local and universal time.

The zone time of some time zones has special names. So, for example, the time of the zero zone is called Western European, the time of the 1st zone is called the Central European, the 2nd zone is called the Eastern European. In the United States, the time of the 16th, 17th, 18th, 19th and 20th zones is called the Pacific, Mountain, Central, Eastern and Atlantic times, respectively.

The territory of the USSR is now divided into 10 time zones, which have numbers from the 2nd to the 11th (see the map of time zones).

On the map of standard time along the meridian of 180 ° longitude, a line for changing the date is drawn.

In order to save and more efficiently distribute electricity during the day, especially in the summer, in some countries in the spring the hands of the clock are moved forward one hour and this time is called summer time. In autumn, the hand goes back an hour.

In our country, in 1930, by a decree of the Soviet government, the clock hands in all time zones were moved one hour forward for the entire time, until canceled (this time was called daylight saving time). This order of time counting was changed in 1981, when the daylight saving time system was introduced (it was introduced temporarily and earlier, until 1930). According to the existing rule, the transition to daylight saving time occurs annually at 2 am on the last Sunday in March, when the clock hands are moved forward 1 hour. It is canceled at 3 am on the last Sunday in September, when the clock hands are moved back 1 hour. Since the temporary translation of the hands is made in relation to the constant time, which is 1 hour ahead of the standard time (it coincides with the previously existing daylight saving time), in the spring and summer months our clocks go 2 hours ahead of the standard time, and in the autumn and winter months - for 1 hour. The capital of our Motherland, Moscow, is located in the 2nd time zone, therefore the time at which they live in this zone (both in summer and in winter) is called Moscow time. According to Moscow time in the USSR, timetables are drawn up for the movement of trains, steamships, airplanes, the time is noted on telegrams, etc.

In ordinary life, the time used in a particular locality is often called the local time of that locality; it should not be confused with the astronomical notion of local time discussed above.

Since 1960, in astronomical yearbooks, the coordinates of the Sun, Moon, planets and their satellites have been published in the ephemeral time system.

Back in the 30s. XX century it was finally established that the Earth rotates around its axis unevenly. With a decrease in the speed of rotation of the Earth, the day (stellar and solar) lengthen, and with an increase in it, they shorten. The magnitude of the average solar day, due to the uneven rotation of the Earth, increases over 100 years by 1-2 thousandths of a second. This very small change is insignificant for a person's everyday life, but it cannot be neglected in some areas of modern science and technology. A uniform system of time counting was introduced - ephemeris time.

Ephemeris time - uniformly current time, which we mean in the formulas and laws of dynamics when calculating the coordinates (ephemeris) of celestial bodies. In order to calculate the difference between ephemeris time and universal time, the coordinates of the moon and planets observed in the universal time system are compared with their coordinates calculated by the formulas and laws of dynamics. This difference was taken equal to zero at the very beginning of the XX century. But since the speed of rotation of the Earth in the XX century. decreased on average, ie the observed days were longer than uniform (ephemeris) days, then the ephemeris time "went" forward relative to universal time, and in 1986 the difference was plus 56 s.

Before the discovery of the unevenness of the Earth's rotation, the derived unit of measure of time - a second - was defined as 1/86400 of the average solar day. The inconstancy of the average solar day due to the uneven rotation of the Earth forced us to abandon such a definition and give the following: "The second is 1 / 31556925.9747 The fraction of the tropical year for 1900, January 0, at 12 o'clock ephemeris time."

The second determined in this way is called ephemeris. The number 31 556 925, 9747, equal to the product 86400 x 365.2421988, is the number of seconds in a tropical year, the duration of which for 1900, January 0, at 12 o'clock ephemeris time was 365.2421988 average solar days.

In other words, the ephemeris second is a time interval equal to 786400 fractions of the average duration of an average solar day, which they had in 1900, in January 0, at 12 o'clock of ephemeris time.

Thus, the new definition of the second is associated with the motion of the Earth in an elliptical orbit around the Sun, while the old definition was based only on its rotation around its axis.

The creation of an atomic clock made it possible to obtain a fundamentally new time scale, independent of the movements of the Earth and called atomic time. In 1967, at the International Conference on Weights and Measures, the atomic second was adopted as a unit of measure of time, defined as "the time equal to 9 192 631 770 periods of radiation of the corresponding transition between two hyperfine levels of the ground state of the cesium-133 atom."

The duration of the atomic second was chosen so that it was as close as possible to the duration of the ephemeris second.

The atomic second is one of the seven basic units of the International System of Units (SI).

The atomic time scale is based on the readings of cesium atomic clocks at observatories and time service laboratories in several countries of the world, including the Soviet Union.

So, we got acquainted with many different systems for measuring time, but we need to clearly imagine that all these different systems of time refer to the same real and objectively existing time. In other words, there are no different times, there are only different units of time and different systems of counting these units.

The shortest period of time that has physical meaning is the so-called Planck time. This is the time it takes for a photon traveling at the speed of light to travel across the Planck length. The Planck length is expressed, in turn, through a formula in which fundamental physical constants are interconnected - the speed of light, the gravitational constant and Planck's constant. In quantum physics, it is believed that at distances less than the Planck length, the concept of continuous space-time cannot be applied. The length of the Planck time is 5.391 16 (13) · 10–44 s.

Greenwich merchants

John Henry Belleville, an employee of the famous Greenwich Observatory in London, thought of selling time back in 1836. The essence of the business was that Mr. Belleville checked his watch daily with the most accurate clocks of the observatory, and then drove around to clients and allowed them to set the exact time on their watches for money. The service turned out to be so in demand that it was inherited by John's daughter, Ruth Belleville, who provided the service until 1940, that is, 14 years after the BBC radio broadcast the first time signals.

No shooting

Modern sprint timing systems have gone far from the days when the judge fired a pistol and the stopwatch was manually started. Since the result now accounts for fractions of a second, which are much shorter than the human reaction time, electronics rule everything. The pistol is no longer a pistol, but a flash-noise device without any pyrotechnics, transmitting the exact start time to the computer. To prevent one runner from hearing the start signal earlier than the other because of the speed of sound propagation, the “shot” is broadcast to the speakers installed next to the runners. False start is also detected electronically using sensors built into the starting blocks of each runner. The finish time is recorded by a laser beam and photocell, as well as by an ultra-fast camera that captures literally every moment.

Second for billions

The world's most accurate atomic clock is from JILA (Joint Institute for Laboratory Astrophysics), a research center based at the University of Colorado, Boulder. This center is a joint project between the University and the US National Institute of Standards and Technology. In watches, strontium atoms cooled to ultra-low temperatures are placed in so-called optical traps. The laser makes atoms vibrate at a rate of 430 trillion vibrations per second. As a result, over 5 billion years the device will accumulate an error of only 1 second.

Atomic strength

Everyone knows that the most accurate clocks are atomic. The GPS system uses the time of an atomic clock. And if the wristwatch is adjusted according to the GPS signal, it will become super accurate. This possibility already exists. The Astron GPS Solar Dual-Time watch, manufactured by Seiko, has a GPS chipset on board, which allows it to check the satellite signal and show extremely accurate time anywhere in the world. And no special energy sources are required for this: Astron GPS Solar Dual-Time is powered only by light energy through panels built into the dial.

Don't anger Jupiter

It is known that on most watches where Roman numerals are used on the dial, the fourth hour is indicated by the symbol IIII instead of IV. Apparently, there is a long tradition behind this "substitution", because there is no exact answer to the question of who and why invented the wrong four. But there are different legends, for example, that since Roman numerals are the same Latin letters, the number IV turned out to be the first syllable of the name of the very revered god Jupiter (IVPPITER). The Romans supposedly considered the appearance of this syllable on the dial of a sundial as blasphemy. From there it all started. Those who do not believe in legends assume that it is design. With the replacement of IV by IIII century. the first third of the dial uses only the number I, the second only the I and V, and the third only the I and X. This makes the dial look neater and more orderly.

Dinosaur Day

Someone lacks 24 hours in a day, but dinosaurs didn't even have that. In ancient geological times, the Earth rotated much faster. It is believed that during the formation of the Moon, a day on Earth lasted two to three hours, and the Moon, which was much closer, orbited our planet in five hours. But gradually the lunar gravity slowed down the rotation of the Earth (due to the creation of tidal waves that are formed not only in water, but also in the crust and in the mantle), while the orbital moment of the Moon increased, the satellite accelerated, moved to a higher orbit, where its speed fell. This process continues to this day, and in a century the days increase by 1/500 s. 100 million years ago, at the height of the dinosaur era, the length of a day was approximately 23 hours.

The abyss of time

Calendars in various ancient civilizations were developed not only for practical needs, but also in close connection with religious and mythological views. Because of this, units of time appeared in the calendar systems of the past, much exceeding the duration of a person's life and even the lifetime of these civilizations themselves. For example, the Maya calendar featured time units such as "baktun", which was 409 years, and epochs of 13 baktun (5125 years). The farthest went the ancient Hindus - in their sacred texts the period of the universal activity of Maha Manvantara, which is 311.04 trillion years, appears. For comparison: according to modern science, the lifetime of the universe is about 13.8 billion years.

Everyone has their own midnight

Unified time systems, time zone systems appeared already in the industrial era, and in the former world, especially in its agrarian part, time counting was organized in its own way in each locality based on the observed astronomical phenomena. Traces of this archaism can be observed today on Mount Athos, in the Greek monastic republic. Here, too, a clock is used, however, the moment of sunset is considered midnight, and the clock is set every day at this moment. Taking into account the fact that some monasteries are located higher in the mountains, while others are lower, and the Sun hides behind the horizon for them at different times, then midnight for them does not come at once.

Live Longer - Live Deeper

The force of gravity slows down the passage of time. In a deep mine, where the Earth's gravitational force is stronger, time passes more slowly than on the surface. And on top of Mount Everest - faster. The effect of gravitational deceleration was predicted by Albert Einstein in 1907 within the framework of general relativity. It took more than half a century to wait for experimental confirmation of the effect, until equipment appeared capable of recording ultra-small changes over time. Today, the most accurate atomic clocks record the effect of gravitational deceleration when the height changes by several tens of centimeters.

Time is stop!

This effect has long been noticed: if a human eye accidentally falls on the watch dial, then the second hand seems to freeze in place for a while, and its subsequent “tick” seems longer than all the others. This phenomenon is called chronostasis (that is, "time distance") and, apparently, goes back to the times when our wild ancestor had a vital need to react to any detected movement. When the gaze falls on the arrow and we detect movement, the brain takes a freeze frame for us, and then quickly brings the sense of time back to normal.

Jumping in time

We, the inhabitants of Russia, are used to the fact that the time in all our many time zones differs by a whole number of hours. But outside of our country, you can find time zones where the time differs from Greenwich by a whole amount plus half an hour or even 45 minutes. For example, the time in India differs from GMT by 5.5 hours, which at one time gave rise to a joke: if you are in London and want to know the time in Delhi, turn the clock over. If you move from India to Nepal (GMT? +? 5.45), then the clock will have to be shifted back 15 minutes, and if to China (GMT? +? 8), which is right there in the neighborhood, then immediately to 3.5 hours ago!

A watch for every challenge

The Swiss company Victorinox Swiss Army has created a watch that can not only show the time and endure the most severe tests (from falling from a height of 10 m onto concrete to moving an eight-ton excavator over it), but also, if necessary, save the life of its owner. They are called I.N.O. X. Naimakka. The bracelet is woven from a special parachute line used to drop heavy military equipment, and in a difficult situation, the wearer can unfasten the bracelet and use the line in many ways: to set up a tent, weave a net or snares, lace up boots, put a splint on a damaged limb and even get fire!

Scent watches

Gnomon, klepsydra, hourglass - all these names of ancient devices for counting time are well known to us. Less known are the so-called fire clock, which in its simplest form is a graduated candle. The candle has burned out by one division - let's say an hour has passed. The people of the Far East were much more inventive in this respect. In Japan and China, there were so-called incense clocks. Instead of candles, incense sticks smoldered in them, and each hour could have its own fragrance. Strings were sometimes tied to sticks, at the end of which a weight was attached. At the right moment, the thread burned out, the weight fell on the sounding plate and the clock struck.

To America and back

The international date line passes in the Pacific Ocean, however, there, on many islands, people live, whose life "between dates" sometimes leads to curiosities. In 1892, American traders persuaded the king of the island kingdom of Samoa to move "from Asia to America" \u200b\u200bby moving east of the date line, for which the islanders had to endure the same day twice - July 4th. More than a century later, the Samoans decided to return everything back, so in 2011 Friday, December 30, was canceled. "Residents of Australia and New Zealand will no longer call us during Sunday service, thinking that we have Monday," - said on this occasion the Prime Minister of the country.

Illusion of the moment

We are used to dividing time into past, present and future, but in a certain (physical) sense, the present is a certain convention. What is happening in the present? We see the starry sky, but the light from each luminous object flies to us at different times - from several light years to millions of years (the Andromeda nebula). We see the sun as it was eight minutes ago.
But even if we are talking about our sensations from nearby objects - for example, from a light bulb in a chandelier or a warm stove that we touch with our hand - it is necessary to take into account the time that passes while the light flies from the light bulb to the retina of the eye or information about sensations moves from nerve endings to the brain. Everything that we feel in the present is a "hodgepodge" of phenomena of the past, far and near.