Astronomy what is year month day. Astronomical basis of the calendar. Calculation of the number of hours

People very early began to use astronomical phenomena to measure time. Much later, they realized that the basic units of such a measurement could not be set arbitrarily, as they depended on certain astronomical laws.

One of the first units of time measurement, of course, was the day, that is, the time during which the Sun, having appeared in the sky, "bypasses" the Earth and reappears at its original point. The division of the day into two parts - day and night facilitated the fixation of this period of time. At different peoples the time of the change of day was associated with the change of day and night. Russian word"day" comes from the ancient "stuck", that is, to connect two parts into a whole, in this case, to connect night and day, light and darkness. In ancient times, the beginning of the day was often considered the sunrise (the cult of the Sun), among Muslims it was the sunset (the cult of the Moon), in our time, the most common boundary between the days is midnight, that is, the time conditionally corresponding to the lower climax of the Sun in a given territory.

The rotation of the Earth around its axis occurs uniformly, however, a number of reasons make it difficult to choose a criterion for accurately determining the day. Therefore, there are concepts: sidereal day, true solar and mean solar day.

A sidereal day is defined by the time interval between two successive upper climaxes of the same star. Their value serves as a standard for measuring the so-called sidereal time; there are, respectively, derivatives of sidereal days (hours, minutes, seconds) and special sidereal hours, without which not a single observatory in the world can do. Astronomy needs to take sidereal time into account.

The usual routine of life is closely connected with other, solar days, with solar time. A solar day is measured by the length of time between successive upper climaxes of the Sun. The duration of a solar day exceeds the stellar day by an average of 4 minutes. In addition, the solar day, due to the uneven movement of the Earth in an elliptical orbit around the Sun, has a variable value. It is inconvenient to use them at home. Therefore, the abstract average solar day, determined by the calculated uniform motion of an imaginary point ("average Sun") along the celestial equator around the Earth, is taken as a standard. average speed movement of the true sun along the ecliptic.

The time interval between two successive climaxes of such an "average Sun" is called the mean solar day.

All hours in Everyday life adjusted to mean time, mean time is also the basis of modern calendars. Average solar time counted from midnight is called civil time.

As a result of the tilt of the ecliptic with respect to the plane of the celestial equator and the tilt of the Earth's axis of rotation with respect to the plane of the Earth's orbit, the length of day and night changes throughout the year. Only during the period of the spring and autumn equinoxes on the entire globe is day equal to night. The rest of the time, the height of the culminations of the Sun changes daily, reaching a maximum for the northern hemisphere during the summer solstice and a minimum during the winter solstice.

The average solar day, like the sidereal ones, is divided into 24 hours, each of which has 60 minutes, and 60 seconds in minutes.

A more fractional division of the day first arose in ancient Babylon and is based on the sexagesimal counting system Volodomonov N. Calendar: past, present, future. Page 88.

Since a day is a relatively short period of time, larger units of its measurement were gradually developed. At first, counting was done with the help of fingers. As a result, such units of time measurement as ten days (decades) and twenty days appeared. Later, an account based on astronomical phenomena was established. The unit of time was taken as the interval between two identical phases of the moon. Since it was easiest to notice the appearance of a narrow lunar crescent after moonless nights, this moment was considered to be the beginning of a new month. The Greeks called it neomenia, that is, the new moon. The day during which the first setting of the young moon was observed was considered the beginning of the calendar month among the peoples who counted according to the lunar calendar. For chronological calculations, the time interval separating the true new moon from neomenia is important. On average, it is 36 hours.

The average length of a synodic month is 29 days, 12 hours, 44 minutes and 3 seconds. In the practice of constructing calendars, a duration of 29.5 days was used, and the accruing difference was eliminated by the special introduction of additional days.

The months of the solar calendar are not associated with the phases of the moon, so their duration was arbitrary (from 22 to 40 days), but on average it was close (30-31 days) to the duration of the synodic month. This circumstance to some extent contributed to the preservation of the count of days by weeks. The seven-day period of time (week) arose not only because of the veneration of the seven gods, corresponding to the seven wandering celestial bodies, but also because seven days made up approximately a fourth of the lunar month.

The number of months in a year accepted in most calendars (twelve) is associated with the twelve zodiacal constellations of the ecliptic. The names of the months often trace their connection with certain seasons, with larger units of time - the seasons.

The third basic unit of time (the year) was less noticeable, especially in the lands closer to the equator, where there is not much difference between the seasons. The value of the solar year, i.e., the period of time during which the Earth makes a revolution around the Sun, was calculated with sufficient accuracy in ancient Egypt, where seasonal changes in nature were of exceptional importance in the economic life of the country. "The need to calculate the periods of rise and fall of the waters of the Nile created Egyptian astronomy."

Gradually, the magnitude of the so-called tropical year, that is, the time interval between two successive passages of the center of the Sun through the vernal equinox, was determined. For modern calculations, the duration of the year is 365 days, 5 hours, 48 ​​minutes and 46 seconds.

In some calendars, years are counted by lunar years, which are associated with a certain number of lunar months and have nothing to do with the tropical year.

In modern practice, the division of the year is widely used not only into months, but also into half-years (6 months) and quarters (3 months).

All people interested in astronomy know that the word "day" has many different values. For example, sidereal day, solar day. But recently many new concepts have arisen for which the same word is used. In this article, we will give more precise definitions.

1. Day as a unit of time

First of all, we recall that the unit of time in astronomy, as in other sciences, is the second of the international system of units SI - the atomic second. Here is the definition of the second as given by the 13th General Conference of Weights and Measures in 1967:

If the word "day" is used to denote a unit of time, it should be understood as 86400 atomic seconds. In astronomy, larger units of time are also used: the Julian year is 365.25 days exactly, the Julian century is 36525 days exactly. The International Astronomical Union (a public organization of astronomers) in 1976 recommended that astronomers use just such units of time. The main time scale, the International Atomic Time (Time Atomic International, TAI), is based on the readings of many atomic clocks in different countries. Hence, from a formal point of view, the basis for measuring time has gone out of astronomy. The old units "mean solar second", "sidereal second" should not be used.

2. A day as a period of rotation of the Earth around its axis

It is somewhat more difficult to define this use of the word "day". There are many reasons for this.

First, the axis of rotation of the Earth, or, scientifically speaking, the vector of its angular velocity, does not maintain a constant direction in space. This phenomenon is called precession and nutation. Secondly, the Earth itself does not maintain a constant orientation relative to its angular velocity vector. This phenomenon is called the movement of the poles. Therefore, the radius vector (a segment from the center of the Earth to a point on the surface) of an observer on the Earth's surface will not return after one revolution (and never at all) to the previous direction. Thirdly, the speed of the Earth's rotation, i.e. the absolute value of the angular velocity vector does not remain constant either. So, strictly speaking, there is no definite period of the Earth's rotation. But with a certain degree of accuracy, a few milliseconds, we can talk about the period of rotation of the Earth around its axis.

In addition, it is necessary to indicate the direction relative to which we will count the revolutions of the Earth. There are currently three such directions in astronomy. This is the direction to the vernal equinox, to the Sun and the celestial ephemeris beginning.

The period of rotation of the Earth relative to the vernal equinox is called a sidereal day. It is equal to 23 h 56 m 04.0905308 s . Note that a sidereal day is a period relative to the spring point, not the stars.

The vernal equinox itself makes complex movement on the celestial sphere, so this number should be understood as an average value. Instead of this point, the International Astronomical Union proposed to use the "celestial ephemeris". We will not give its definition (it is rather complicated). It is chosen so that the period of the Earth's rotation relative to it is close to the period relative to the inertial reference frame, i.e. relative to stars, or more precisely, extragalactic objects. The angle of rotation of the Earth relative to this direction is called the sidereal angle. It is equal to 23 h 56 m 04.0989036 s , slightly more than a sidereal day by the amount by which the spring point shifts in the sky due to precession per day.

Finally, consider the rotation of the Earth relative to the Sun. This is the most difficult case, since the Sun moves in the sky not along the equator, but along the ecliptic and, moreover, unevenly. But these sunny days are obviously the most important for people. Historically, the atomic second has been adjusted to the period of the Earth's rotation relative to the Sun, with the averaging done around the 19th century. This period is equal to 86400 units of time, which were called mean solar seconds. The adjustment took place in two steps: first, "ephemeris time" and "ephemeris second" were introduced, and then the atomic second was set equal to the ephemeris second. Thus, the atomic second still "comes from the Sun", but the atomic clock is a million times more accurate than the "terrestrial clock".

The rotation period of the Earth does not remain constant. There are many reasons for this. These are seasonal changes in the distribution of temperature and air pressure around the globe, and internal processes, and external influences. Distinguish secular slowdown, decade (for decades) irregularities, seasonal and sudden. On fig. 1 and 2 are graphs showing the change in the length of the day in 1700-2000. and in 2000-2006. On fig. 1, there is a trend towards an increase in the day, and in Fig. 2 - seasonal unevenness. The graphs are based on the materials of the International Earth Rotation and Reference Systems Service (IERS, http://www.iers.org/).

Is it possible to return the basis of measuring time to astronomy and is it worth it? Such a possibility exists. These are pulsars whose rotation periods are conserved with great accuracy. Besides, there are a lot of them. It is possible that over long time intervals, for example, decades, observations of pulsars will serve to refine atomic time and a "pulsar time" scale will be created.

The study of the uneven rotation of the Earth is very important for practice and is interesting with scientific point vision. For example, satellite navigation is impossible without knowledge of the rotation of the Earth. And its features carry information about the internal structure of the Earth. This complex problem awaits its researchers.

Rice. 1. Difference of the Earth's rotation period from 86400 s SI, in milliseconds. Data up to the beginning of the 20th century. are not very reliable, but the trend towards an increase in the length of the day is clearly visible.

Man began to take an active interest in the measurement of time when he realized that practical benefits could be derived from this.


First of all, it was necessary to accurately predict the change of seasons, which made it possible to plan ahead for upcoming agricultural work. As a result, such basic concepts as a year, a month and a day have firmly entered the culture of all modern peoples, and at the same time, into the representation of each individual person.

But only in the Middle Ages, numerous studies of the starry sky made it possible to reveal the true essence of the observed astronomical phenomena. As a result scientific knowledge acquired several interpretations of basic temporal terms, which, however, not everyone knows.

What is a year?

Initially, a year meant a full cycle of seasons (winter, spring, summer, autumn). Only after the creation of the heliocentric theory was it proved that the concept of the year is inextricably linked (as well as by the tilt of the earth's axis). To improve the accuracy of calculating the trajectories of celestial bodies and solving other astronomical problems, it was necessary to clearly define the term "year", as a result of which several interpretations of it appeared:

Tropical year: the time interval during which the Sun returns to its original position on the celestial sphere (from the point of view of an observer on the surface of the Earth). Duration - 365 days 5 hours 48 minutes 45.19 seconds (changes slightly every year).

Sidereal: the time period during which the Earth makes a complete revolution around the Sun and returns to the starting point (the count is relative to the stars, the position of which on the celestial sphere changes very slowly). Duration - 365 days 6 hours 9 minutes 8.97 seconds.

Anomaly year: the time period during which our planet returns to a certain point in its own orbit - the periapsis. Duration - 365 days 6 hours 13 minutes 52.6 seconds.

Calendar year: a time span that approximates a complete seasonal cycle. Duration 365 days (in the Gregorian calendar).


It is worth noting that in the modern calendar every 4 years there is an increase in the annual cycle by one day. This is due to the fact that the "extra" quarters of the day at the end of each year are summed up and added to every fifth year.

What is a month?

The concept of the month is also associated with the modern calendar by most people. However, historically, the 30-day cycle is tied to the lunar calendar, or rather, to the 29-day period of a complete change of phases of the only satellite of our planet. Such a month is called synodic and lasts 29 days 12 hours 44 minutes and 2.8 seconds. By analogy with the year, the (lunar) month can also be tropical, sidereal, and anomalistic.

Most peoples gave the name to a particular month in accordance with its properties, but it is difficult to trace such patterns in the modern Gregorian calendar. The fact is that the names of the months in this system are borrowed from the Latin Julian calendar, so if you translate them into Russian, they will get an unambiguous meaning: September is the seventh, October is the eighth, August is named after Octavian Augustus, July is named after Julius Caesar, etc.

What is a day?

From an astronomical point of view, a day is the period of a complete rotation of the Earth around its axis, so this term does not have such a variety of interpretations as a year and a month. Scientists distinguish the earth day (a full day / night cycle, visible to an observer from the surface of the Earth. Duration - 24 hours) and sidereal days (a full cycle for an outside observer. Duration - 23 hours 56 minutes 4 seconds).

This difference is explained by the fact that during the day our planet moves somewhat along its orbit, therefore, in order to complete the cycle for an earthly observer, the planet must “turn around” a little. It is also worth noting that the division of the day into 24 hours is an absolutely conditional division, which is dictated by the cultural characteristics of European culture (there are examples in history of how different peoples divided the day into 10, 22, 30 parts, which, moreover, could be different by duration).


Due to the action of the forces of gravity of the Sun, the speed of rotation of our planet slows down very slowly, as a result of which the length of the day increases. For example, 500 million years ago there were only 20.5 hours in a day, therefore, for every century this important time period increases by 2 milliseconds.

It would seem that the concept of a month is familiar to everyone, but not many people are able to answer the question of what a month is. Consider the concept of a month as a unit of time.

What is called the month

A month refers to a full revolution of the moon around the Earth. It is believed that this unit of measurement originated many thousands of years ago, long before the birth of Jesus Christ. There are several types of months in astronomy.

• The first month is synodic. It represents the time interval between the same phases of the moon, is approximately 29.5 days.
• The so-called stellar month is also the period of time, which includes a full revolution of the moon around the earth during the apparent movement of the moon on the celestial sphere. The sidereal month is 27 days long.
• In a tropical month, the period of revolution of the Moon around the Earth is measured in longitude. Due to the peculiarity of the earth's axis, the tropical month is shorter than the sidereal month. This feature called the precession of the earth's axis. The tropical month is also approximately 27 days long.

What is a calendar month

A calendar month is understood as the period of time from the first day to the last day of a particular month. Note that the calendar month is often not related to astronomical months, but its origin is directly related to astronomical observations. In particular, the modern calendar months originated from the lunar and solar-lunar calendars, which are actively used in Hinduism, Chinese calendars, Muslims and Jews. In these calendars, the number of days in a month ranges from 29 to 30.

Calendar history

However, the ancestor of the calendar months is traditionally considered to be Julius Caesar. Before him, the ancient Romans also used their calendar, but initially there were not 12 months in it, but 10. The names of the months were numerals. Then the names of the months were changed to the names of the gods, for example, January was named after the two-faced god Janus, February - in honor of the god of the underworld Februs.

In many ways, the ancient Roman calendar was determined by superstition. Initially, it consisted of 304 days, but the Romans sought to fit it into the ancient Greek calendar, which consisted of 354 days. However, even numbers were considered unlucky by the Romans, so one more day had to be added to the calendar, thus the calendar became 12 months long. However, it was extremely inconvenient to use, it was difficult to predict weather phenomena, and, consequently, the preparation for the harvest.

How was the Julian calendar invented?

In this regard, the Roman statesman Julius Caesar attempted to reform the calendar. Having visited Egypt, he considered that the Egyptian calendar was much better than the Roman one. After his visit to Egypt, he commissioned astronomers to modify the Roman calendar. The process of creating the Julian calendar was led by the astronomer Sosigen, but the Roman Senate, first of all, thanked Julius Caesar for creating the new calendar. The month of July was even named after him.

Calendar Improvement

Note that the Julian calendar has been improved for a long time. Initially, there were no numbers in this calendar, the days were distributed according to nones, calends and eve. Obviously, such a system of calculating months was very difficult to understand. It generated a lot of controversy, especially in military affairs. For example, to say the date of July 15, they said “17th day from the July kalends”, May 9th was called “7th day from the May ides”. Of course, this confused many, and even chroniclers sometimes could not explain the meaning of concepts. And in military affairs, it was important to act quickly and be able to plan tactics as well as possible. Therefore, the preservation of such a system was out of the question. And since Julius Caesar was a commander highly respected by the Senate, he was able to carry out other reforms of the calendar, which successfully took root among both the civilian population and the military.

Thus, the Julian calendar has undergone major changes, but its general features have been preserved, and to this day many countries use it. It should be noted that the Julian calendar is not accurate. It lags behind the tropical year by 11 minutes 14 seconds, in terms of chronology, this is 128 years for one day. However, its main advantage over other calendars is its ease of use.

If you do not understand why there are 12 months in a year, we recommend that you read the article.

Federal Agency for Education of the Russian Federation

State educational institution higher professional education

AMUR STATE UNIVERSITY

(GOU VPO "AmSU")

on the topic: Astronomical foundations of the calendar

by discipline: Concepts of modern natural science

Executor

student of group C82 B

Supervisor

Ph.D., Associate Professor

Blagoveshchensk 2008

• Introduction
• 1 Prerequisites for the appearance of the calendar
• 2 Elements of spherical astronomy
• 2.1 Main points and lines of the celestial sphere
• 2.2 Celestial coordinates
• 2.3 The culmination of the luminaries
• 2.4 Days, sidereal day
• 2.5 Mean solar time
• 2.6 Standard, maternity and summer time
• 3 Change of seasons
• 3.1 Equinoxes and solstices
• 3.2 Sidereal year
• 3.3 Zodiac constellations
• 3.4 Characteristic rising and setting stars
• 3.5 Tropical, Bessel year
• 3.6 Precession
• 3.7 Change in the number of days in a year
• 4 Change of phases of the moon
• 4.1 Sidereal month
• 4.2 Configurations and phases of the moon
• 4.3 Synodic month
• 5 Seven-day week
• 5.1 Origin of the seven-day week
• 5.2 Names of the days of the week
• 6 Calendar arithmetic
• 6.1 Lunar calendar
• 6.2 Lunisolar calendar
• 6.3 Solar calendar
• 6.4 Features of the Gregorian calendar
• Conclusion
• List of sources used

INTRODUCTION

Natural science is a system of natural sciences, including cosmology, physics, chemistry, biology, geology, geography and others. the main objective studying it - knowledge of the essence (truth) of natural phenomena by formulating laws and deriving consequences from them /1/.

The training course "Concepts of modern natural science" was introduced relatively recently into the system higher education and is currently the basis of natural science education in the training of qualified personnel in the humanities and socio-economic specialties at Russian universities.

The primary goal of education is to introduce a new member of society to the culture created over the thousand-year history of mankind. The concept of "cultural person" is traditionally associated with a person who is freely oriented in history, literature, music, painting: the emphasis, as we see, falls on humanitarian forms of reflection of the world. However, in our time, the understanding has come that the achievements of the natural sciences are an integral and most important part of human culture. The peculiarity of the course is that it covers an extremely wide subject area.

The purpose of writing this essay is to understand the astronomical foundations of the calendar, the reasons for its occurrence, as well as the origin of individual concepts, such as a day, a week, a month, a year, the systematization of which led to the appearance of the calendar.

1 BACKGROUND TO THE CALENDAR

In order to use time units (day, month, year), people of antiquity needed to be aware of them, then learn how to count how many times in some period of time separating the events of interest to them, this or that unit of account fit. Without this, people simply could not live, communicate with each other, trade, farm, etc. At first, such a time account could be very primitive. But in the future, as human culture developed, with the increase in the practical needs of people, calendars improved more and more, the concepts of the year, month, week appeared as their constituent elements.

The difficulties that arise in the development of the calendar are due to the fact that the length of the day, the synodic month and the tropical year are incommensurable with each other. It is not surprising, therefore, that in the distant past, each tribe, each city, state created their own calendars, composing months and years from days in different ways. In some places, people considered time as units close to the duration of a synodic month, taking a certain (for example, twelve) number of months in a year and not taking into account the change in season. This is how lunar calendars appeared. Others measured time in the same months, but the length of the year sought to be consistent with the changes in the seasons (lunisolar calendar). Finally, others took the change of seasons as the basis for counting days, and did not take into account the change in the phases of the moon at all (solar calendar).

Thus, the task of constructing a calendar consists of two parts. First, on the basis of long-term astronomical observations, it was necessary to establish as accurately as possible the duration of the periodic process (tropical year, synodic month), which is taken as the basis of the calendar. Secondly, it was necessary to select calendar units for counting whole days, months, years of various durations and establish the rules for their alternation in such a way that for sufficiently long periods of time the average duration of a calendar year (as well as a calendar month in lunar and lunisolar calendars) was close to the tropical year (respectively, the synodic month).

In their practical activities, people could not do without a certain era - the counting system (chronology). In the distant past, each tribe, each settlement created its own calendar system and its own era. At the same time, in some places, years were counted from some real event (for example, from the coming to power of one or another ruler, from a devastating war, flood or earthquake), in others - from a fictitious, mythical event, often associated with religious beliefs of people . The starting point of this or that era is usually called its era.

All evidence of the events of bygone days had to be put in order, to find their appropriate place on the pages of a single world history. This is how the science of chronology arose (from the Greek words "chronos" - time and "logos" - a word, a doctrine), the task of which is to study all forms and methods of counting time, compare and determine the exact dates of various historical events and documents, and more broadly - to find out the age of the remains of material culture found during archaeological excavations, as well as the age of our planet as a whole. Chronology is such a scientific area in which astronomy comes into contact with history.

2 ELEMENTS OF SPHERICAL ASTRONOMY

2.1 Main points and lines of the celestial sphere

When studying the appearance of the starry sky, they use the concept of the celestial sphere - an imaginary sphere of arbitrary radius, to inner surface which, as it were, "suspended" stars. The observer is located in the center of this sphere (at point O) (Figure 1). The point of the celestial sphere, located directly above the observer's head, is called the zenith, the opposite of it is called the nadir. The points of intersection of the imaginary axis of rotation of the Earth ("axis of the world") with the celestial sphere are called the poles of the world. Let us draw three imaginary planes through the center of the celestial sphere: the first is perpendicular to the plumb line, the second is perpendicular to the axis of the world, and the third is through the plumb line (through the center of the sphere and the zenith) and the axis of the world (through the pole of the world). As a result, we get three large circles on the celestial sphere (the centers of which coincide with the center of the celestial sphere): the horizon, the celestial equator and the celestial meridian. The celestial meridian intersects with the horizon at two points: the north point (N) and the south point (S), the celestial equator - at the east point (E) and the west point (W). The SN line, which defines the north-south direction, is called the noon line.

Figure 1 - The main points and lines of the celestial sphere; the arrow indicates the direction of its rotation

The apparent annual movement of the center of the solar disk among the stars occurs along the ecliptic - a great circle, the plane of which makes an angle e = 23 ° 27 / with the plane of the celestial equator. The ecliptic intersects with the celestial equator at two points (Figure 2): at the vernal equinox T (March 20 or 21) and at the point autumn equinox(September 22 or 23).

2.2 Celestial coordinates

As on a globe - a reduced model of the Earth, on the celestial sphere, you can build a coordinate grid that allows you to determine the coordinates of any star. The role of the earth's meridians on the celestial sphere is played by declination circles passing from the north pole of the world to the south, instead of earthly parallels, daily parallels are drawn on the celestial sphere. For each luminary (Figure 2) you can find:

1. Angular distance A its circle of declination from the vernal equinox, measured along the celestial equator against the daily movement of the celestial sphere (similar to how we measure geographic longitude along the earth's equator X- angular distance of the meridian of the observer from the zero Greenwich meridian). This coordinate is called the star's right ascension.

2. Angular distance of the luminary b from the celestial equator - the declination of the luminary, measured along the circle of declinations passing through this luminary (corresponds to geographic latitude).

Figure 2 - The position of the ecliptic on the celestial sphere; the arrow indicates the direction of the apparent annual motion of the Sun

Right ascension of the star A measured in hours - in hours (h or h), minutes (m or t) and seconds (s or s) from 0h to 24h declination b- in degrees, with a plus sign (from 0° to +90°) in the direction from the celestial equator to the north celestial pole and with a minus sign (from 0° to -90°) - to the south celestial pole. In the process of daily rotation of the celestial sphere, these coordinates for each luminary remain unchanged.

The position of each luminary on the celestial sphere at a given time can be described by two other coordinates: its azimuth and angular height above the horizon. To do this, from the zenith through the luminary to the horizon, we mentally draw a large circle - the vertical. Azimuth of the star A measured from south S to the west to the point of intersection of the vertical of the star with the horizon. If the azimuth is counted counterclockwise from the south point, then a minus sign is attributed to it. Luminary height h is counted along the vertical from the horizon to the luminary (Figure 4). Figure 1 shows that the height of the celestial pole above the horizon is equal to the geographic latitude of the observer.

2.3 The culmination of the luminaries

During the daily rotation of the Earth, each point of the celestial sphere passes twice through the celestial meridian of the observer. The passage of one or another luminary through that part of the arc of the celestial meridian, on which the zenith of the observer is located, is called the upper culmination luminaries. In this case, the height of the luminary above the horizon reaches its maximum value. At the moment of the lower climax the luminary passes the opposite part of the meridian arc, on which the nadir is located. The time elapsed after the upper culmination of the luminary is measured by the hour angle luminaries U.

If the luminary in the upper climax passes through the celestial meridian south of the zenith, then its height above the horizon at that moment is equal to:

2.4 Day, sidereal day

Gradually rising upward, the Sun reaches its highest position in the sky (the moment of the upper culmination), after which it slowly sinks down to hide behind the horizon again for several hours. 30 - 40 minutes after sunset, when the evening twilight ends , the first stars appear in the sky. This correct alternation of day and night, which is a reflection of the rotation of the Earth around its axis, gave people a natural unit of time - day.

So, a day is a period of time between two successive culminations of the same name of the Sun. For the beginning of true solar days take the moment of the lower culmination of the center of the solar disk (midnight). In accordance with the tradition that came to us from Ancient Egypt and Babylonia, the day is divided into 24 hours, each hour into 60 minutes, each minute into 60 seconds. Time T0 , measured from the lower culmination of the center of the solar disk, is called true solar time.

But the earth is a sphere. Therefore, its own (local) time will be the same only for points located on the same geographical meridian.

We have already spoken about the rotation of the Earth around its axis relative to the Sun. It turned out to be convenient and even necessary to introduce another unit of time - a sidereal day, as the time interval between two successive climaxes of the same name of the same star. Since, rotating around its axis, the Earth also moves in its orbit, the sidereal day is shorter than the solar day by almost four minutes. In a year, there are exactly one more sidereal days than solar days.

The moment of the upper culmination of the vernal equinox is taken as the beginning of the sidereal day. Hence, sidereal time is the time that has elapsed since the upper culmination of the vernal equinox. It is measured by the hour angle of the vernal equinox. Sidereal time is equal to the right ascension of the luminary, which is currently in the upper climax (at this time, the hourly angle of the luminary t = 0).

The equation of time says that the true Sun in its movement on the celestial sphere either “overtakes” the average sun, then “lags behind” it, and if time is measured by the average sun, then shadows from all objects are cast due to their illumination by the true Sun . Suppose someone decides to build a building facing south. The noon line will indicate the desired direction to him: at the moment of the upper culmination of the Sun, when it, crossing the celestial meridian, "passes over the point of the south", the shadows from vertical objects fall along the noon line towards the north. Therefore, to solve the problem, it is enough to hang a weight on the thread and, at the mentioned moment of time, drive in pegs along the shadow cast by the thread.

But it is impossible to establish "by eye" when the center of the Sun's disk crosses the celestial meridian, this moment should be calculated in advance.

We use sidereal time to determine which parts of the starry sky (constellations) will be visible above the horizon at one time or another of the day and year. At each particular moment of time, those stars are in the upper climax for which A= 5. Calculating sidereal time s, and determine the conditions for the visibility of stars and constellations.

2.5 Mean solar time

Measurements show that the duration of a true solar day varies throughout the year. They have the greatest length on December 23, the smallest on September 16, and the difference in their duration on these days is 51 seconds. This is due to two reasons:

1) uneven movement of the Earth around the Sun in an elliptical orbit;

2) the inclination of the axis of the Earth's daily rotation to the plane of the ecliptic.

Obviously, it is impossible to use such an unstable unit as a true day when measuring time. Therefore, in astronomy, the concept of the average sun was introduced . This is a fictitious point that moves uniformly along the celestial equator throughout the year. The time interval between two successive climaxes of the same name of the mean sun is called the mean solar day. The time measured from the lower climax of the mean sun is called the mean solar time. It is the mean solar time that our clock shows, we use it in all our practical activities.

2.6 Standard, maternity and summer time

At the end of the last century, the globe was divided every 15 ° in longitude into 24 time zones. So that inside each belt having a number N(N varies from 0 to 23), the clock indicated the same standard time - TP - the mean solar time of the geographic meridian passing through the middle of this belt. When moving from belt to belt, in the direction from west to east, the time at the border of the belt jumps up by exactly one hour. As a zero zone, a belt is taken, located (in longitude) in the band ±7°.5 from the Greenwich meridian. The mean solar time of this zone is called grisnvich or world.

In many countries of the world, in the summer months of the year, the transition to the time of the neighboring time zone located to the east is practiced.

Russia has also introduced summer time: on the night of the last Sunday in March, the clock hands are moved one hour ahead of maternity time, and at night on the last Sunday of September they return back.

3 CHANGE OF THE SEASONS

3.1 Equinoxes and solstices

Rotating around its axis, the Earth at the same time moves around the Sun at a speed of 30 km / s. In this case, the imaginary axis of the daily rotation of the planet does not change its direction in space, but is transferred parallel to itself. Therefore, the value of the declination of the Sun during the year continuously (and, moreover, at different speeds) changes. So, on December 21 (22) it has the smallest value, equal to -23 ° 27 ", after three months, on March 20 (21) it is equal to zero °, then on June 21 (22) it reaches the maximum value + 23 ° 27 /, 22 ( 23) of September again becomes equal to zero, after which the declination of the Sun continuously decreases until December 21. But in spring and autumn, the rate of change in declination is quite large, while in June and December it is much less. a certain distance from the celestial equator for several days.December 21 - 22 in the northern hemisphere, the height of the Sun above the horizon at its upper climax is the smallest, this day is the shortest of the year, followed by the longest night of the year at the winter solstice.On the contrary, in summer , June 21 or 22, the height of the Sun above the horizon at the upper culmination is greatest, this day of the summer solstice has the longest duration.The vernal equinox occurs on March 20 or 21 (the Sun in its apparent annual movement passes through the vernal equinox point from the southern hemisphere to the northern), and September 22 or 23 is the autumnal equinox. On these dates, the length of day and night is equalized. Under the influence of attraction acting on the Earth from other planets, the parameters of the Earth's orbit, in particular its inclination to the plane of the celestial equator e, change: the plane of the Earth's orbit seems to "stagger" and for millions of years this value fluctuates around its average value.

The Earth revolves around the Sun in an elliptical orbit, and therefore its distance from it varies somewhat throughout the year. Our planet is closest to the Sun (at present) on January 2-5, at which time the speed of its movement in orbit is the greatest. Therefore, the duration of the seasons of the year is not the same: spring - 92 days, summer - 94 days, autumn - 90 and winter - 89 days for the northern hemisphere. Spring and summer (the number of days elapsed from the moment the Sun passes through the vernal equinox to its passage through the autumn equinox) in the northern hemisphere lasts 186 days, while autumn and winter - 179. Several thousand years ago, the "elongation" of the ellipse of the earth's orbit was smaller, therefore, the difference between the mentioned time intervals was also smaller. In connection with the change in the height of the Sun above the horizon, a regular change of seasons occurs. Cold winter with its severe frosts, long nights and short days, it gives way to a flowering spring, then a fruitful summer, followed by autumn.

3.2 Sidereal year

Comparing the view of the starry sky immediately after sunset from day to day for several weeks, you can see that the apparent position of the Sun in relation to the stars is constantly changing: the Sun moves from west to east and makes a full circle in the sky every 365.256360 days , returning to the same star. This period of time is called a sidereal year.

3.3 Zodiac constellations

For better orientation in the boundless ocean of stars, astronomers divided the sky into 88 separate areas - constellations. According to 12 constellations, which are called zodiac, and the Sun passes throughout the year.

In the past, about 2000 years ago, and even in the Middle Ages, for convenience in counting the position of the Sun on the ecliptic, it was divided into 12 equal parts of 30 ° each. Each 30° arc was designated by the sign of the zodiacal constellation through which the Sun passed in a given month. So the signs of the Zodiac appeared in the sky. The starting point was the vernal equinox, which was at the beginning of BC. e. in the constellation Aries. An arc 30° long measured from it was indicated by the sign "ram's horns". Further, the Sun passed through the constellation Taurus, so the ecliptic arc from 30 to 60 ° was designated by the “sign of Taurus”, etc. Calculations of the position of the Sun, Moon and planets in the “signs of the Zodiac”, i.e. actually at certain angular distances from the point equinoxes have been held for many centuries to compile horoscopes.

3.4 Characteristic rising and setting stars

Due to the continuous movement of the disk of the Sun on the celestial sphere from west to east, the view of the starry sky from evening to evening, although slowly, but continuously changes. So, if at a certain time of the year some constellation of the zodiac an hour after sunset is visible in the southern part of the sky (say, it passes through the celestial meridian), then due to the indicated movement of the Sun on each subsequent evening this constellation will pass through the meridian four minutes earlier than in the previous one. By the time the sun sets, it will move more and more into the western part of the sky. In about three months, this zodiac constellation will already disappear in the rays of the evening dawn, and after 10-20 days it will be visible already in the morning before sunrise in the eastern part of the sky. Other setting constellations and individual stars behave in much the same way. At the same time, the change in the conditions of their visibility significantly depends on the geographic latitude of the observer and the declination of the luminary, in particular, on its distance from the ecliptic. So, if the stars of the zodiacal constellation are far enough from the ecliptic, then in the morning they are visible even before their evening visibility ceases.

The first appearance of a star in the rays of the morning dawn (i.e., the first morning sunrise of a star) is called its heliacal (from the Greek "helios" - the Sun) sunrise. With each subsequent day, this star manages to rise higher and higher above the horizon: after all, the Sun continues its annual movement across the sky. Three months later, by the time the Sun rises, this star, together with “its” constellation, is already passing the meridian (in the upper culmination), and after another three months it will be hiding behind the horizon in the west.

The sunset of a star in the rays of the morning dawn, which occurs only once a year (morning sunset), is commonly called its cosmic (“cosmos” - “decoration”) sunset. Further, the rising of a star above the horizon in the east at sunset (sunrise in the rays of the evening dawn) is called its acronic sunrise (from the Greek "akros" - the highest; apparently, the position most distant from the Sun was meant). And, finally, the setting of a star in the rays of the evening dawn is usually called a heliacal setting.

3.5 Tropical, Bessel year

When the Sun moves along the ecliptic. On March 20 (or 21) the center of the Sun's disk crosses the celestial equator, passing from the southern hemisphere of the celestial sphere to the northern one. The point of intersection of the celestial equator with the ecliptic - the point of the vernal equinox is in our time in the constellation Pisces. In the sky, it is not "marked" by any bright star; astronomers establish its location in the celestial sphere with very high accuracy from observations of "reference" stars close to it.

The time interval between two successive passages of the center of the Sun's disk through the vernal equinox is called the true or tropical year. Its duration is 365.2421988 days, or 365 days 5 hours 48 minutes and 46 seconds. It is assumed that the mean sun also returns to the vernal equinox in the same time.

The duration of our calendar year is not the same: it contains either 365 or 366 days. Meanwhile, astronomers count tropical years of the same duration. At the suggestion of the German astronomer F. W. Bessel (1784-1846), the beginning of the astronomical (tropical) year is taken as the moment when the right ascension of the mean equatorial sun is 18h40m.

3.6 Precession

The tropical year is 20 minutes 24 seconds shorter than the sidereal year. This is due to the fact that the vernal equinox at a speed of 50 "2 per year moves along the ecliptic towards the annual movement of the Sun. This phenomenon was discovered by the ancient Greek astronomer Hipparchus in the 2nd century BC and was called precession, or precession of the equinoxes. In 72 years, the vernal equinox moves along the ecliptic by 1º, in 1000 years - by 14 °, etc. In about 26,000 years, it will make a full circle on the celestial sphere.In the past, about 4,000 years ago, the vernal equinox point was in the constellation Taurus not far from the Pleiades star cluster, while the summer solstice at that time came at the moment the Sun passed through the constellation Leo near the star Regulus.

The phenomenon of precession occurs because the shape of the Earth is different from spherical (our planet is, as it were, flattened at the poles). Under the influence of attraction by the Sun and the Moon of various parts of the "flattened" Earth, the axis of its daily rotation describes a cone around the perpendicular to the plane of the ecliptic. As a result, the celestial poles move among the stars in small circles with radii of about 23°27/. At the same time, the entire grid of equatorial coordinates is shifting on the celestial sphere, and from it the vernal equinox point. Due to precession, the appearance of the starry sky on a certain day of the year is slowly but continuously changing.

3.7 Change in the number of days in a year

As observations of stellar culminations carried out over many decades have shown, the rotation of the Earth around its axis is gradually slowing down, although the magnitude of this effect is still known with insufficient accuracy. It is assumed that over the past two thousand years, the length of the day has increased by an average of 0.002 s per century. This, it would seem, is an insignificantly small value, accumulating, leads to very noticeable results. Because of this, for example, there will be inaccurate calculations of the moments of solar eclipses and the conditions for their visibility in the past.

In our time, the value of the tropical year decreases every century by 0.54 s. It is estimated that a billion years ago, the day was 4 hours shorter than today, and in about 4.5 billion years, the Earth will make only nine revolutions around its axis per year.

4 MOON PHASE CHANGE

Probably the first of the astronomical phenomena that primitive man paid attention to was the change in the phases of the moon. It was she who allowed him to learn to count the days. And it is no coincidence that in many languages ​​the word "month" has common root, consonant with the roots of the words "measure" and "Moon", for example, Latin mensis - month and mensura - measure, Greek "mene" - Moon and "men" - month, English moon - Moon and month - month. Yes, and the Russian national name of the moon is a month.

4.1 Sidereal month

Observing the position of the Moon in the sky over several evenings, it is easy to verify that it moves among the stars from west to east at an average speed of 13°.2 per day. The angular diameter of the Moon (as well as the Sun) is approximately 0.5. It can be said, therefore, that for every day the Moon moves to the east by 26 of its diameters, and in one hour - by more than the value of its diameter. Having made a full circle on the celestial sphere, the Moon after 27.321661 days (=27d07h43mlls,5) returns to the same star. This period of time is called a sidereal (ie, stellar: sidus is a star in Latin) month.

4.2 Configurations and phases of the moon

As you know, the Moon, whose diameter is almost 4, and the mass is 81 times less than that of the Earth, revolves around our planet at an average distance of 384,000 km. The surface of the Moon is cold and glows with reflected sunlight. When the Moon revolves around the Earth or, as they say, when the configurations of the Moon change (from the Latin configuro - I give the correct shape) - its positions relative to the Earth and the Sun, that part of its surface that is visible from our planet is illuminated by the Sun unequally. The consequence of this is the periodic change in the phases of the moon. When the Moon, during its movement, finds itself between the Sun and the Earth (this position is called a conjunction), it faces the Earth with its unlit side, and then it is not visible at all. This is a new moon.

Appearing then in the evening sky, first in the form of a narrow crescent, the Moon after about 7 days is already visible in the form of a semicircle. This phase is called the first quarter. After about 8 days, the Moon occupies a position directly opposite to the Sun and its side facing the Earth is completely illuminated by it. There comes a full moon, at this time the moon rises at sunset and is visible in the sky all night. 7 days after the full moon, the last quarter comes, when the moon is again visible in the form of a semicircle, turned by a bulge in the other direction, and rises after midnight. Recall that if at the time of the new moon the shadow of the moon falls on the Earth (more often it slips “above” or “below” our planet), a solar eclipse occurs. If the full moon is immersed in the shadow of the earth, a lunar eclipse is observed.

4.3 Synodic month

The period of time after which the phases of the moon repeat again in the same order is called the synodic month. It is equal to 29.53058812 days = 29d12h44m2s.8. Twelve synodic months are 354.36706 days. Thus, the synodic month is incommensurable neither with the day nor with the tropical year: it does not consist of a whole number of days and does not fit without a trace in the tropical year.

The indicated duration of the synodic month is its average value, which is obtained as follows: they calculate how much time has elapsed between two eclipses far apart from each other, how many times during this time the Moon has changed its phases, and divide the first value by the second (and select several pairs and find average value). Since the Moon moves around the Earth in an elliptical orbit, the linear and observed angular velocities of its movement at different points of the orbit are different. In particular, this latter varies from about 11° to 15° per day. The movement of the Moon becomes very complicated and the force of attraction acting on it from the side of the Sun, because the magnitude of this force is constantly changing both in its numerical value and in direction: it has highest value in the new moon and the smallest - in the full moon. The actual duration of the synodic month varies from 29d6h15m to 29d19h12m

5 SEVEN DAY WEEK

5.1 Origin of the seven-day week

Artificial units of time measurement, consisting of several (three, five, seven, etc.) days, are found among many peoples of antiquity. In particular, the ancient Romans and Etruscans counted the days as "eight days" - trading weeks, in which the days were denoted by letters from A to H; seven days of such a week were working days, the eighth days were market days. These market days also became days of festivities.

The custom of measuring time with a seven-day week came to us from Ancient Babylon and, apparently, is associated with a change in the phases of the moon. In fact, the duration of the synodic month is 29.53 days, and people saw the Moon in the sky for about 28 days: the moon phase continues to increase from a narrow crescent to the first quarter for seven days, about the same from the first quarter to the full moon, etc.

But observations of the starry sky gave one more confirmation of the "exclusivity" of the number seven. At one time, ancient Babylonian astronomers discovered that, in addition to fixed stars, seven “wandering” stars were also visible in the sky, which were later called planets (from the Greek word “planetes”, which means “wandering”). It was assumed that these luminaries revolve around the Earth and that their distances from it increase in this order: the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn. In ancient Babylon, astrology arose - the belief that the planets influence the fate of individuals and entire nations. Comparing certain events in people's lives with the position of the planets in the starry sky, astrologers believed that the same event would occur again if this arrangement of the luminaries was repeated. The very same number seven - the number of planets - became sacred both for the Babylonians and for many other peoples of antiquity.

5.2 Names of the days of the week

Dividing the day into 24 hours, the ancient Babylonian astrologers made up the idea that every hour of the day is under the auspices of a certain planet, which, as it were, “controls” it. The counting of hours was started from Saturday: the first hour was "ruled" by Saturn, the second by Jupiter, the third by Mars, the fourth by the Sun, the fifth by Venus, the sixth by Mercury and the seventh by the Moon. After that, the cycle was repeated again, so that the 8th, -15th and 22nd hours were “ruled” by Saturn, the 9th, 16th and 23rd by Jupiter, etc. As a result, it turned out that the first the hour of the next day, Sunday, was “ruled” by the Sun, the first hour of the third day was the Moon, the fourth was Mars, the fifth was Mercury, the sixth was Jupiter, and the seventh was Venus. Accordingly, the days of the week got their names. Astrologers depicted the successive change of these names as a seven-pointed star inscribed in a circle, at the tops of which the names of the days of the week, planets and their conventions(figure 00).

Figure 3 - Astrological images of the change of days of the week

These names of the days of the week, the names of the gods, migrated to the Romans, and then to the calendars of many peoples. Western Europe.

In Russian, the name of the day passed to the entire seven days (a week, as it was once called). So Monday is "the first day after the week", Tuesday is the second day, Thursday is the fourth, Friday is the fifth, and Wednesday was indeed the average day. It is curious that in the Old Slavonic language there is also its more ancient name - the third one.

In conclusion, it should be noted that the seven-day week spread in the Roman Empire under the emperor Augustus (63 BC - 14 AD) in connection with the passion of the Romans for astrology. In particular, wall images of the seven gods of the days of the week were found in Pompeii. The very wide distribution and “survivability” of a time interval of seven days is apparently associated with the presence of certain psychophysiological rhythms. human body appropriate duration.

6 ARITHMETIC OF CALENDARS

Nature has provided people with three periodic processes that allow them to keep track of time: the change of day and night, the change in the phases of the moon, and the change of seasons. On their basis, such concepts as day, month and year were formed. However, the number of days in both a calendar year and a calendar month (as well as the number of months in a year) can only be an integer. Meanwhile, their astronomical prototypes are the synodic month And tropical year - contain fractional parts of the day. “Therefore,” says Professor N. I. Idelson (1885-1951), a well-known specialist in the “calendar problem,” from Leningrad, “the calendar unit inevitably turns out to be erroneous against its astronomical prototype; over time, this error accumulates and calendar dates no longer correspond to the astronomical state of affairs. How to equalize these discrepancies? This is a purely arithmetic problem; it leads to the establishment of calendar units with an unequal number of days (for example, 365 and 366, 29 and 30) and to the determination of the rules for their alternation. calendar units with an unequal number of days (for example, simple and leap years), the calendar problem can be considered solved. According to the figurative expression of N. I. Idelson, the calendar system “receives its course, as it were, independently of astronomy” and, “referring to the calendar, we should not at all ... focus on those astronomical facts and relationships from which it is derived.” And vice versa: "The calendar, which remains in constant contact with astronomy, becomes cumbersome and inconvenient"

6.1 Lunar calendar

When considering the theory lunar calendar the duration of the synodic month with a sufficient degree of accuracy can be taken equal to 29.53059 days. Obviously, the calendar month corresponding to it can contain 29 or 30 days. The calendar lunar year consists of 12 months. The corresponding duration of the astronomical lunar year is:

12X29.53059 = 354.36706 days.

Therefore, it can be assumed that the calendar lunar year consists of 354 days: six “full” months of 30 days and six “empty” months of 29 days, since 6 X 30 + 6 X 29 = 354. And in order to start the calendar month, how can more precisely coincided with the new moon, these months should alternate; for example, all odd months can contain 30 days, and all even months can contain 29 days.

However, the time interval of 12 synodic months is 0.36706 days longer than the calendar lunar year of 354 days. For three such years, this error will already be 3X0.36706= 1.10118 days. Consequently, in the fourth year from the beginning of the count, the new moons will already fall not on the first, but on the second days of the months, after eight years - on the fourth, etc. This means that the calendar should be corrected from time to time: approximately every three years do an insertion on one day, i.e. instead of 354 days, count 355 days in a year. A year of 354 days is usually called a simple year, a year of 355 days is called an extended or leap year.

The task of constructing a lunar calendar is as follows: to find such an order of alternation of prime and leap years lunar years, in which the beginning of the calendar months would not move noticeably from the new moon.

Experience shows that for every 30 years (one cycle), the new moons move forward 0.0118 days in relation to the first number of calendar months, and this gives a shift of one day in about 2500 years.

6.2 Lunisolar calendar

Theory. The theory of lunisolar calendars is based on two astronomical quantities:

1 tropical year = 365.242 20 days;

1 synodic month = 29.530 59 days.

From here we get:

1 tropical year = 12.368 26 synodic months.

In other words, a solar year contains 12 full lunar months and about one third more. Therefore, a year in the lunisolar calendar can consist of 12 or 13 lunar months. In the latter case, the year is called embolic(from the Greek "embolismos" - insert).

Note that in Ancient Rome And medieval Europe the insertion of an additional day or month was called intercalation (from the Latin intercalatio - insertion), and the added month itself was called intercalary.

In the lunisolar calendar, the beginning of each calendar month should be as close as possible to the new moon, and the average length of the calendar year over the cycle should be close to the length of the tropical year. The insertion of the 13th month is made from time to time so that the beginning of the calendar year is kept as close as possible to some point in the astronomical solar year, for example, to the equinox.

6.3 Solar calendar

The solar calendar is based on the length of the tropical year - 365.24220 days. This immediately shows that the calendar year can contain either 365 or 366 days. The theory must indicate the order in which simple (365 days) and leap years (366 days) alternate in any particular cycle, so that the average length of the calendar year per cycle is as close as possible to the length of the tropical year.

Thus, the cycle consists of four years, and during this cycle one insertion is made. In other words, out of every four years, three years have 365 days, the fourth has 366 days. Such a system of leap years existed in the Julian calendar. On average, the duration of such a calendar year is 0.0078 days longer than the duration of the tropical year, and this difference for about 128 years is a whole day.

Since 1582, the countries of Western Europe, and later many other peoples of the world, switched to counting time according to the Gregorian calendar, the project of which was developed by the Italian scientist Luigi Lilio (1520-1576). The duration of the calendar year here is assumed to be 365.24250 days. In accordance with the value of the fractional part of the year / (= 0.2425 = 97/400, in a time interval of 400 years, an additional 366th day is inserted 97 times in a year, i.e., compared to the Julian calendar, here three days in 400 years are thrown out .

Second calendar system - new julian calendar, proposed by the Yugoslav astronomer Milutin Milanković (1879-1956). In this case, the average length of a calendar year is 365.24222.

The insertions of the additional 366th day of the year must be made here 218 times every 900 years. This means that in comparison with the Julian in the New Julian calendar, 7 days are thrown out every 900 years. It is proposed to consider leap years those century years in which the number of hundreds when divided by 9 gives a remainder of 2 or 6. The next such years, starting from 2000, will be another 2400, 2900, 3300 and 3800. The average duration of the New Julian calendar year is longer than the length of the year tropical by 0.000022 mean solar days. And this means that such a calendar gives a discrepancy of a whole day only for 44,000 years.

6.4 Features of the Gregorian calendar

In the Gregorian calendar, a simple year also has 365 days, a leap year 366. As in the Julian calendar, every fourth year is a leap year - the one whose serial number in our chronology is divisible by 4 without a remainder. At the same time, however, those century years of the calendar, the number of hundreds of which is not divisible by 4 without a remainder, are considered simple (for example, 1500, 1700, 1800, 1900, etc.). Leap years are the centuries 1600, 2000, 2400, etc. Thus, the full cycle of the Gregorian calendar consists of 400 years; By the way, the first such cycle ended quite recently, October 15, 1982, and it contains 303 years of 365 days and 97 years of 366 days.

The error of this calendar in one day runs over 3300 years. Therefore, in terms of the accuracy and clarity of the leap year system (which facilitates its memorization), this calendar should be considered very successful.

CONCLUSION

A long time ago, man noticed the cyclical nature of many natural phenomena. The sun, having risen above the horizon, does not remain hanging overhead, but descends on the western side of the sky in order to rise again after some time in the east. The same happens with the Moon. Long warm summer days give way to short and cold winter days and vice versa. Periodic phenomena observed in nature served as the basis for counting time.

The most popular period of time is the day, defined by the change of day and night. It is known that this change is due to the rotation of the Earth around its axis. For the calculation of large periods of time, a day is of little use, a large unit is needed. These were the period of the change of the phases of the moon - a month, and the period of the change of seasons - a year. The month is due to the rotation of the Moon around the Earth, and the year is due to the rotation of the Earth around the Sun. Of course, small and large units had to be correlated with each other, i.e. bring into a single system. Such a system, as well as the rules for its application for measuring large periods of time, became known as a calendar.

It is customary to call a calendar a certain system of counting long periods of time with their subdivisions into separate shorter periods (years, months, weeks, days).

The need to measure time arose among people already in ancient times, and certain methods of counting time, the first calendars arose many millennia ago, at the dawn of human civilization.

LIST OF USED SOURCES

1. Archakov I.Yu. Planets and stars. St. Petersburg: Delta, 1999.

2. Gorelov A.A. Concepts of modern natural science. M.: Center, 2000.

3. Dunichev V.M. Concepts of modern natural science: Teaching aid / Dunichev V.M. - Yuzhno-Sakhalinsk: Sakhalin book publishing house, 2000. - 124 p.

4. Klimishin I.A. Calendar and chronology M: "Nauka" Main edition of physical and mathematical literature, 1985, 320 s

5. Moore P. Astronomy with Patrick Moore / per. from English. M.: FAIR - PRESS, 1999.