Time is the most important philosophical, scientific and practical category. The choice of a method for measuring time has been of interest to man since ancient times, when practical life became associated with the periods of revolution of the sun and moon. Despite the fact that the first clock - solar - appeared three and a half millennia BC, this problem remains quite complicated. Often, answering the simplest question related to it, for example, "how many hours are there in a day," is not so simple.

History of timekeeping

The alternation of light and dark times of the day, periods of sleep and wakefulness, work and rest began to mean for people the passage of time as early as primitive times. Every day the sun moved across the sky during the day, from sunrise to sunset, and the moon - at night. It is logical that the period between the same phases of the movement of the luminaries has become a unit of time calculation. Day and night gradually formed into a day - a concept that determines the change of date. On their basis, shorter units of time appeared - hours, minutes and seconds.

For the first time, they began to determine how many hours in a day, ancient times. The development of knowledge in astronomy led to the fact that day and night began to be divided into equal periods associated with sunrise celestial equator certain constellations. And the Greeks adopted the sexagesimal number system from the ancient Sumerians, who considered it the most practical.

Why exactly 60 minutes and 24 hours?

To count anything ancient man I used what is usually always at hand - fingers. From here originates the decimal number system adopted in most countries. Another method, based on the phalanges of the four fingers of the open palm of the left hand, flourished in Egypt and Babylon. In the culture and science of the Sumerians and other peoples of Mesopotamia, the number 60 became sacred. In many cases, it was possible to divide it without a trace by the presence of many divisors, one of which is 12.

The mathematical concept of how many hours there are in a day originates in Ancient Greece. The Greeks at one time took into account in the calendar only daylight hours days and divided the time from sunrise to sunset into twelve equal intervals. Then they did the same with night time, resulting in a 24-part division of the day. Greek scientists knew that the length of the day changes throughout the year, so for a long time there were day and night hours, which were the same only on the days of the equinox.

From the Sumerians, the Greeks also adopted the division of the circle into 360 degrees, on the basis of which a system of geographical coordinates was developed and the division of the hour into minutes (minuta prima (lat.) - "reduced first part" (of the hour)) and seconds (secunda divisio (lat.) - "second division" (hours)).

solar day

The meaning of the day regarding the interaction of celestial objects is the length of time during which the Earth makes full turn around the axis of rotation. It is customary for astronomers to make several clarifications. They highlight solar day- the beginning and end of the revolution is considered by the location of the Sun at the same point in the celestial sphere - and they are divided into true and average.

It is impossible to say to the nearest second how many hours in a day that are called true solar hours without specifying a specific date. During the year, their duration periodically changes by almost a minute. This is due to the unevenness and complex trajectory of the movement of the star along celestial sphere- the axis of rotation of the planet has an inclination of about 23 degrees relative to the plane of the celestial equator.

More or less accurately, you can say how many hours and minutes are in a day, which experts refer to as average solar. This is the usual, used in Everyday life calendar periods of time that define a specific date. They are considered to be of constant duration, that they are exactly 24 hours, or 1440 minutes, or 86,400 seconds. But this statement is also conditional. It is known that the speed of rotation of the Earth is decreasing (a day lengthens by 0.0017 seconds in a hundred years). The intensity of the planet's rotation is influenced by complex gravitational cosmic interactions and spontaneous geological processes within it.

sidereal day

Modern requirements for calculations in space ballistics, navigation, etc. are such that the question of how many hours a day lasts requires a solution with an accuracy of nanoseconds. For this, more stable reference points are chosen than nearby celestial bodies. If we calculate the full turnover the globe, taking as the initial moment its position relative to the vernal equinox, you can get the duration of the day, called stellar.

Modern science accurately determines how many hours in a day that bear the beautiful name of stellar - 23 hours 56 minutes 4 seconds. Moreover, in some cases, their duration is even more specified: the true number of seconds is 4.0905308333. But even this scale of refinements is sometimes insufficient: the constancy of the reference point is affected by the unevenness orbital movement planets. To eliminate this factor, a special, ephemeris origin of coordinates is chosen, associated with extragalactic radio sources.

Time and calendar

The final version of determining how many hours in a day, close to modern, was adopted in ancient Rome, with the introduction julian calendar. Unlike the ancient Greek time system, the day was divided into 24 equal intervals, regardless of the time of day and season.

AT different cultures their own calendars are used, which have specific events as a starting point, most often of a religious nature. But the duration of the average solar day is the same throughout the Earth.

How long are the days? A strange question: we know from childhood that a day is exactly 24 hours, or 1440 minutes or 86400 seconds. Yes, not so. A day is a period of time during which the Earth makes one complete rotation around its axis, and it turns out that it never takes exactly 24 hours.

How long does a day last?

If we take as a starting point distant star, and consider the period for which it returns to the same point as days, it turns out that one revolution of our planet takes 23 hours 56 minutes and 4 seconds! That is, in a day, astronomical midnight can creep away by almost 4 minutes! Moreover, this period is called a sidereal day, depending on the friction caused by synoptic situations, tides, and geological events changes all the time in the range up to 50 seconds. If we take our Sun as a reference point, as our ancestors did, then the number is already closer to 24 hours. This is called a solar day. On average, for a year, taking into account the revolution of the planet around the sun, a solar day is a fraction of a second shorter than twenty-four hours.

When these discrepancies were revealed using the most accurate atomic clock, it was decided to redefine the second as a fixed fraction of a "solar" day, - more precisely, one million six hundred and forty thousandth.

The new second came into use in 1967 and is defined as "a time interval equal to 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom in the absence of perturbation external fields". You can’t say more precisely - it’s just too dreary to pronounce all this at the end of a long day.

The new definition of the second means that the solar day gradually shifts in relation to the atomic. As a result, scientists had to introduce the so-called "leap second" (or "jump second") into the atomic year in order to align the atomic year with the solar year.

Since 1972, leap seconds have been added 23 times. Imagine, otherwise our day would have increased by almost half a minute. And the Earth continues to slow down its rotation. And, according to scientists, in the 23rd century there will be 25 current hours in our day.

The last time a "leap second" was added was on December 31, 2005, at the direction of the International Service for Estimating the Parameters of the Rotation and Coordinates of the Earth, based at the Paris Observatory.

Good news for astronomers and those of us who like clocks to keep pace with the Earth's movement around the Sun, but a headache for computer programs and all the equipment that is on space satellites.

The idea of ​​introducing a "leap second" met with a decisive rebuff from International Union telecommunications, which even made a formal proposal to abolish it entirely back in December 2007.

Of course, you can wait until the difference between Coordinated Universal Time (UTC) and Greenwich Mean Time (GMT) reaches exactly one hour (somewhere in 400 years) and even then put everything in order. In the meantime, the debate around what counts as "real" time continues.

How long does a day last?

If we take a distant star as a reference point, and count the period during which it returns to the same point as days, it turns out that one revolution of our planet takes 23 hours 56 minutes and 4 seconds! That is, in a day, astronomical midnight can creep away by almost 4 minutes! Moreover, this period, called a sidereal day, depending on the friction caused by synoptic situations, tides and geological events, changes all the time in the range of up to 50 seconds. If we take our Sun as a reference point, as our ancestors did, then the number is already closer to 24 hours. This is called a solar day. On average, for a year, taking into account the revolution of the planet around the sun, a solar day is a fraction of a second shorter than twenty-four hours.

When these discrepancies were revealed with the help of the most accurate atomic clocks, it was decided to redefine the second as a fixed fraction of a "solar" day, - more precisely, one million six hundred and forty thousandth.

The new second came into use in 1967 and is defined as "a time interval equal to 9,192,631,770 radiation periods corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom in the absence of disturbance by external fields." You can’t say more precisely - it’s just too dreary to pronounce all this at the end of a long day.

The new definition of the second means that the solar day gradually shifts in relation to the atomic. As a result, scientists had to introduce the so-called "leap second" (or "jump second") into the atomic year in order to align the atomic year with the solar year.

Since 1972, leap seconds have been added 23 times. Imagine, otherwise our day would have increased by almost half a minute. And the Earth continues to slow down its rotation. And, according to scientists, in the 23rd century there will be 25 current hours in our day.

The last time a "leap second" was added was on December 31, 2005, at the direction of the International Service for Estimating the Parameters of the Rotation and Coordinates of the Earth, based at the Paris Observatory.

Good news for astronomers and those of us who love clocks to keep pace with the Earth around the Sun, but a headache for computer programs and all the hardware that goes on space satellites.

The idea of ​​introducing a "leap second" met with a strong rebuff from the International Telecommunications Union, which even made a formal proposal to completely abolish it back in December 2007.

Of course, you can wait until the difference between Coordinated Universal Time (UTC) and Greenwich Mean Time (GMT) reaches exactly one hour (somewhere in 400 years) and even then put everything in order. In the meantime, the debate around what counts as "real" time continues.

August 10, 2016

Everyone knows it - 24 hours. But why did it happen? Let's take a closer look at the history of basic units measure time and find out how many hours, seconds and minutes are in a day. And also let's see if it is worth tying these units exclusively to astronomical phenomena.

Where did the day come from? This is the time of one rotation of the earth around its axis. Still knowing little about astronomy, people began to measure time in such ranges, including in each light and dark time.

But there is interesting feature. When does the day start? FROM modern point everything is obvious - the day begins at midnight. People of ancient civilizations thought otherwise. It is enough to look at the very beginning of the Bible in order to read in the 1st book of Genesis: "... and there was evening, and there was one morning." The day began with There is a certain logic in this. The people of that time were guided by the Sun, the village was over, the day was over. Evening and night is the next day.

But how many hours are there in a day? Why was the day divided into 24 hours, because the decimal system is more convenient, and much more? If there were, say, 10 hours in a day, and 100 minutes in each hour, would something change for us? Actually, nothing but numbers, on the contrary, it would even be more convenient to make calculations. But the decimal system is far from the only one used in the world.

They used the sexagesimal counting system. And the bright half of the day was well divided in half, for 6 hours each. In total, there were 24 hours in a day. This rather convenient division was taken from the Babylonians and other peoples.

Among the ancient Romans, counting time was even more interesting. The countdown started at 6 am. So they counted further from this moment - the first hour, the third hour. Thus, it can be easily calculated that the "eleventh hour workers" commemorated by Christ are those who start work at five o'clock in the evening. Indeed, too late!

At six o'clock in the evening came the twelfth hour. That's how many hours in a day were counted in ancient Rome. But it was still night time! The Romans did not forget about them either. After the twelfth hour, the night watch began. The attendants changed at night every 3 hours. Evening and night time was divided into 4 guards. The first evening watch began at 6 pm and lasted until 9. The second, midnight watch, lasted from 9 to 12 o'clock. The third watch, from 12 at night to 3 in the morning, ended when the roosters sang, which is why it was called “rooster crow”. The last, fourth watch was called "morning" and ended at 6 in the morning. And everything started all over again.

The need to divide watches into component parts also arose much later, but they did not retreat from the sexagesimal system even then. And then the minute was divided into seconds. True, it later became clear that it was impossible to rely only on the determination of the duration of seconds and days. For a century, the length of the day increases by 0.0023 seconds - it seems to be very little, but enough to get confused about how many seconds are in a day. And that's not all the difficulties! Our Earth does not make one revolution around the Sun in an even number of days, and this also affects the solution of the question of how many hours are in a day.

Therefore, to simplify the situation, a second was equated not to movement celestial bodies, and by the time of the processes inside the cesium-133 atom at rest. And to match the actual state of affairs with the revolution of the Earth around the Sun twice a year - on December 31 and June 30 - 2 extra leap seconds are added, and once every 4 years - an additional day.

In total, it turns out that there are 24 hours in a day, or 1440 minutes, or 86400 seconds.