Astronomy what is year month day. Astronomical foundations of the calendar. Calculating the number of hours

People very early started using astronomical phenomena to measure time. Much later, they realized that the basic units of such a measurement cannot be set arbitrarily, since they depend 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 the original point. Dividing the day into two parts, day and night, facilitated the fixation of this time interval. For different peoples, the time of the change of day was associated with the change of day and night. The Russian word "day" comes from the ancient "knuckle", that is, to connect two parts of 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 rising of the Sun (the cult of the Sun), among the Muslims - the setting of the Sun (the cult of the Moon), in our time the most common border between the days is midnight, that is, the time conditionally corresponding to the lower culmination of the Sun in a given territory.

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

Sidereal days are defined by the time interval between two successive upper climaxes of one star. Their magnitude 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 no observatory in the world can do. Astronomy needs to take sidereal time into account.

The usual routine of life is closely related to other, sunny days, with solar time. Solar days are 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, solar days, due to the uneven motion of the Earth in an elliptical orbit around the Sun, have a variable magnitude. It is inconvenient to use them in everyday life. Therefore, an abstract average solar day, determined by the calculated uniform motion of an imaginary point ("average Sun") along the celestial equator around the Earth with the average speed of the true Sun along the ecliptic, is taken as a standard.

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

Every watch in everyday life is adjusted to the average time, the average time is also the basis of modern calendars. Average solar time 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 the day and night changes throughout the year. Only during the period of the vernal and autumnal equinoxes all over the globe is the day equal to the night. The rest of the time, the height of the Sun's culminations changes daily, reaching a maximum for the northern hemisphere at the summer solstice and a minimum at the winter solstice.

Average solar days, as well as stellar ones, are divided into 24 hours, each of which has 60 minutes, 60 seconds in minutes.

A more fractional division of the day first appeared in Ancient Babylon and is based on the sixtiethical system of counting Volodomonov N. Calendar: past, present, future. P. 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 fingers. As a result, such time units as ten days (decades) and twenty days appeared. Later, an account based on astronomical phenomena was established. The time unit 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 neomeny, 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 were counting according to the lunar calendar. For chronological calculations, the time interval separating the true new moon from neomeny 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 accumulating difference was eliminated by a 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 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 the day for weeks. The seven-day period of time (week) arose not only because of the worship of the seven gods, corresponding to the seven wandering celestial bodies, but also because seven days were approximately a quarter of the lunar month.

The number of months in a year (twelve) accepted in most calendars 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 major unit of time (year) was less perceptible, especially in lands lying closer to the equator, where there is not much difference between seasons. The magnitude of the solar year, that is, the period of time during which the Earth revolves 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 water in the Nile created Egyptian astronomy."

Gradually, the size of the so-called tropical year was determined, that is, the time interval between two successive passages of the center of the Sun through the vernal equinox. For modern calculations, the length of the year is 365 days, 5 hours, 48 \u200b\u200bminutes and 46 seconds.

In some calendars, years are counted in lunar years associated with a specific number of lunar months and not related to a tropical year.

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

All people interested in astronomy know that the word "day" has many different meanings. For example, a sidereal day, a solar day. But recently, many new concepts have emerged that use the same word. 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 it was 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 astronomers to use just such units of time. The main time scale, Time Atomic International (TAI), is based on the readings of many atomic clocks in different countries. Consequently, from a formal point of view, the basis for measuring time has left astronomy. The old units "mean solar second", "sidereal second" should not be used.

2. Day as the period of rotation of the Earth around the axis

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

First, the Earth's axis of rotation, 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 the vector of its angular velocity. This phenomenon is called pole movement. Therefore, the radius vector (a segment from the center of the Earth to a point on the surface) of an observer on the surface of the Earth will not return after one revolution (and never at all) to the previous direction. Thirdly, the speed of rotation of the Earth, i.e. the absolute value of the angular velocity vector does not remain constant either. So, strictly speaking, there is no specific rotation period for the Earth. But with a certain degree of accuracy, a few milliseconds, we can talk about the period of the Earth's rotation 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 three such directions in astronomy now used. 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 sidereal days. It is equal to 23 h 56 m 04.0905308 s. Note that a sidereal day is a period relative to the point of spring, not stars.

The vernal equinox itself makes a complex movement on the celestial sphere, therefore this number should be understood as an average value. Instead of this point, the International Astronomical Union suggested using the "celestial ephemeris origin". We will not define it (it is rather complicated). It was chosen so that the period of rotation of the Earth relative to it was close to the period relative to the inertial frame of reference, i.e. relative to stars or, more precisely, extragalactic objects. The angle of rotation of the Earth relative to this direction is called the stellar 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 was adjusted to the period of rotation of the Earth relative to the Sun, and the averaging was 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, the "ephemeris time" and the "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 "Earth clock".

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

Is it possible to return the basis of time measurement to astronomy and is it worth doing? This possibility exists. These are pulsars, the periods of rotation of which are conserved with great accuracy. In addition, many of them are known. It is not excluded that over long periods of time, 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 interesting from a scientific point of view. For example, satellite navigation is impossible without knowledge of the Earth's rotation. And its features carry information about the internal structure of the Earth. This difficult problem awaits its researchers.

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

A person began to take an active interest in measuring time when he realized that practical benefits could be derived from this.


First of all, this was necessary for accurately predicting the change of seasons, which made it possible to plan in advance the upcoming agricultural work. As a result, such basic concepts as year, month and 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 has acquired several interpretations of basic temporal terms, which, however, are not known to everyone.

What is a year?

Initially, the year meant a full cycle of changes of the 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 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 for which the Sun returns to its original position on the celestial sphere (from the point of view of an observer on the Earth's surface). Duration - 365 days 5 hours 48 minutes 45.19 seconds (varies slightly every year).

Sidereal: the time period during which the Earth makes a full revolution around the Sun and returns to the starting point (the counting 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.

Anomalous year: the time interval for 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 period that roughly indicates the full seasonal cycle. Duration 365 days (in the Gregorian calendar).


It should be noted 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?

Most people also associate the concept of the month with the modern calendar. However, historically, the 30-day cycle is tied to the lunar calendar, or rather to the 29-day period of the complete phase change 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 this or that month in accordance with its properties, but in the modern Gregorian calendar it is difficult to trace such patterns. 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 in honor of Julius Caesar, etc.

What is a day?

From an astronomical point of view, a day is a period of a complete revolution of the Earth around its axis, therefore this term does not have such a variety of interpretations as a year and a month. Scientists distinguish the Earth's day (a full day / night cycle, visible to an observer from the Earth's surface. Duration - 24 hours) and a sidereal day (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 in its orbit, therefore, to complete the cycle for the terrestrial 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 (in history there are examples 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 Sun's gravitational forces, the rotation speed of our planet slows down very slowly, with the result that the length of the day increases. For example, 500 million years ago there were only 20.5 hours in a day, therefore, for each century, this important time interval 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. Let's consider the concept of a month as a unit of time.

What is called a month

The month means a complete 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 sidereal month is also a period of time, which includes a complete revolution of the moon around the earth with the apparent movement of the moon in the celestial sphere. The duration of a sidereal month reaches 27 days.
• In the tropical month, the period of the Moon's revolution around the Earth is measured in longitude. Due to the peculiarity of the earth's axis, the tropical month is shorter than the stellar month. This feature is called the precession of the earth's axis. The tropical month is also approximately 27 days.

What is a calendar month

A calendar month means a 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, Julius Caesar is traditionally considered to be the ancestor of calendar months. Before him, the ancient Romans also used their own calendar, but initially the months were not 12, 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 in honor of 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 among the Romans, so one more day had to be added to the calendar, so the calendar became 12 months old. However, in handling it was extremely inconvenient, it was difficult to predict weather events, and, consequently, preparation for the harvest.

How the Julian calendar was invented

In this regard, the Roman statesman Julius Caesar made an attempt to reform the calendar. Having visited Egypt, he considered that the Egyptian calendar is 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 Sozigen, however, the Roman Senate, first of all, thanked Julius Caesar for the creation of the new calendar. The month of July was even named after him.

Improving the calendar

Note that the Julian calendar has been improving for a long time. Initially, there were no numbers in this calendar, the days were distributed according to nons, calendars and eves. Obviously, this system of counting months was very difficult to understand. She gave rise to a lot of controversy, especially in military affairs. For example, to say the date of July 15th they said "17th day from the July calendars", May 9th was called "7th day from the Id of May". Of course, many were confused and even chroniclers sometimes could not explain the meaning of the concepts. And in military affairs, it was important to act quickly and be able to plan tactics as best 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 calendar reforms, 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, however, that the Julian calendar is not accurate. It lags behind the tropical year by 11 minutes 14 seconds, from the point of view of chronology it is 128 years for one day. However, its main advantage over other calendars is ease of use.

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

Federal Agency for Education of the Russian Federation

State educational institution of 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 С82 В

Leader

ph.D., associate professor

Blagoveshchensk 2008

• Introduction
• 1 Prerequisites for the appearance of the calendar
• 2 Elements of spherical astronomy
• 2.1 Major points and lines of the celestial sphere
• 2.2 Celestial coordinates
• 2.3 The culmination of the luminaries
• 2.4 Day, stellar day
• 2.5 Average solar time
• 2.6 Standard time, daylight saving time and summer time
• 3 Changing seasons
• 3.1 Equinoxes and Solstices
• 3.2 Star Year
• 3.3 Zodiac constellations
• 3.4 Typical Star Rises and Sets
• 3.5 Tropical, Bessel year
• 3.6 Precession
• 3.7 Changing the number of days in a year
• 4 Changing the phases of the moon
• 4.1 Sidereal month
• 4.2 Moon configurations and phases
• 4.3 Synodic month
• 5 Seven-day week
• 5.1 Origin of the seven-day week
• 5.2 Names of days of the week
• 6 Calendar arithmetic
• 6.1 Lunar calendar
• 6.2 Lunar-solar 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 that includes cosmology, physics, chemistry, biology, geology, geography, and others. The main goal of studying it is the 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 of higher education and is currently the basis of natural science education in the preparation of qualified personnel in the humanities and socio-economic specialties in 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 "cultured person" is traditionally associated with a person who is free to navigate 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. A feature 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 certain concepts, such as day, week, month, year, the systematization of which led to the appearance of the calendar.

1 BACKGROUND OF THE APPEARANCE OF THE CALENDAR

To use units of time measurement (day, month, year), people of antiquity had to understand them, then learn how to calculate how many times in some period of time separating the events of interest to them, one or another unit of account was fitted. Without this, people simply could not live, communicate with each other, trade, engage in agriculture, etc. At the beginning, such a timing could be very primitive. But later, with the development of human culture, with the increase in the practical needs of people, calendars were more and more improved, the concepts of a year, a month, a week appeared as their constituent elements.

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

Thus, the problem of building a calendar consists of two parts. First, on the basis of many years of 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 the calendar units for counting whole days, months, years of various durations and to establish the rules for their alternation in such a way that for sufficiently long periods of time the average length 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 this or that ruler, from a devastating war, flood or earthquake), in others - from a fictional, mythical event, often associated with religious beliefs of people. ... The starting point of reference 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, doctrine), the task of which is to study all forms and methods of reckoning time, to compare and determine the exact dates of various historical events and documents, and in a broader sense - 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 a scientific field in which astronomy meets history.

2 ELEMENTS OF SPHERICAL ASTRONOMY

2.1 Major points and lines of the celestial sphere

When studying the appearance of the starry sky, the concept of the celestial sphere is used - an imaginary sphere of an arbitrary radius, to the inner surface of which the stars are, as it were, "suspended". 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 head of the observer, is called the zenith, and the opposite point is 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's 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 Sun's disk among the stars occurs along the ecliptic - a large circle, the plane of which makes an angle of e \u003d 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 autumn equinox (September 22 or 23).

2.2 Celestial coordinates

As on the 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 terrestrial meridians on the celestial sphere is played by the circles of declination, passing from the north pole of the world to the south; instead of terrestrial parallels, diurnal parallels are drawn on the celestial sphere. For each luminary (Figure 2) you can find:

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

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

Figure 2 - 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 luminary and measured in hourly units - 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 pole of the world and with a minus sign (from 0 ° to -90 °) - to the south pole of the world. During the daily rotation of the celestial sphere, these coordinates for each star remain unchanged.

The position of each star 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 draw a mentally large circle - a vertical. The azimuth of the star ANDmeasured from the south point S to the west to the point of intersection of the vertical of the star with the horizon. If the azimuth is counted from the south point counterclockwise, then a minus sign is assigned to it. Luminary height h is measured along the vertical from the horizon to the luminary (Figure 4). Figure 1 shows that the height of the pole of the world above the horizon is equal to the latitude of the observer.

2.3 The culmination of the luminaries

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

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

2.4 Day, starry day

Gradually rising up, the Sun reaches its highest position in the sky (the moment of the upper culmination), after which it slowly descends to hide behind the horizon for several hours. 30-40 minutes after sunset, when evening twilight ends , the first stars appear in the sky. This is the correct alternation of day and night, which is a reflection of the rotation of the Earth around its axis, and 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 disk of the Sun (midnight). In accordance with the tradition that came to us from Ancient Egypt and Babylonia, the day is divided into 24 hours, every hour - 60 minutes, each minute - 60 seconds. Time T0 measured from the lower culmination of the center of the Sun's disk is called true solar time.

But the Earth is a ball. Therefore, its own (local) time will be the same only for points located on the same geographic meridian.

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

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

The equation of time says that the true Sun in its motion on the celestial sphere sometimes "overtakes" the average sun, then "lags behind" it, and if time is measured by the average sun, then the shadows from all objects are cast due to their illumination by the true Sun ... Suppose someone decides to build a building facing south. The desired direction will be indicated by the midday line: at the moment of the upper culmination of the Sun, when it crosses the celestial meridian, “passes over the point of the south”, the shadows from vertical objects fall along the midday line towards the north. Therefore, to solve the problem, it is enough to hang a weight on the threads and, at the mentioned moment of time, drive the 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 any given moment in time, the upper climax contains those stars for which and \u003d 5. Calculating the sidereal time s, and determine the conditions for the visibility of stars and constellations.

2.5 Average solar time

Measurements show that the duration of true solar days throughout the year is not the same. They have the greatest length on December 23, the shortest on September 16, and the difference in their duration on the indicated 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 evenly along the celestial equator throughout the year. The time interval between two consecutive climaxes of the same name of the average sun is called the average solar day. The time measured from the lower climax of the average sun is called the average solar time. It is the average solar time that our watches show, we use them in all our practical activities.

2.6 Zone, Daylight Savings Time and Daylight Saving Time

At the end of the last century, the globe was broken every 15 ° in geographic longitude into 24 time zones. So that inside each belt numbered N (N varies from 0 to 23), the hours indicated the same standard time - Tp - the mean solar time of the geographic meridian passing through the middle of this belt. When passing from belt to belt, in the direction from west to east, the time at the border of the belt increases abruptly by exactly one hour. The belt located (in longitude) in the strip is taken as zero. ± 7 °, 5from the Greenwich meridian. The average solar time of this belt is called grisnvichskyor worldwide.

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

Russia has also introduced summertime: on the night of the last Sunday in March, the clock hands move one hour ahead of standard time, and on the night of the last Sunday in September, it moves back.

3 CHANGE OF 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 planet's daily rotation does not change its direction in space, but is carried parallel to itself. Therefore, the declination of the Sun changes continuously throughout the year (and, moreover, at different rates). 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 highest value + 23 ° 27 /, 22 ( 23) September again becomes zero, after which the declination of the Sun decreases continuously until December 21. But in spring and autumn, the rate of change in declination is quite high, while in June and December it is much slower. 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 in its upper culmination is the lowest; this day of the year is the shortest, followed by the longest night of the winter solstice of the year. , June 21 or 22, the height of the Sun above the horizon at the upper climax is greatest, this day of the summer solstice has the longest duration. On March 20 or 21, the vernal equinox begins (the Sun in its apparent m of the annual movement passes through the vernal equinox from the southern hemisphere to the northern), and on September 22 or 23 - the autumn equinox. On these dates, the length of the day and night are equalized. Under the influence of the 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 over 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 changes somewhat throughout the year. Our planet is closest to the Sun (currently) on January 2-5, at which time its orbital speed is greatest. Therefore, the length of the seasons of the year is not the same: spring - 92 days, summer - 94 days, autumn - 90 days 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 transition through the autumnal equinox) in the northern hemisphere last 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. Due to the change in the height of the Sun above the horizon, there is a natural change in the seasons. Cold winter with its fierce frosts, long nights and short days gives way to blooming spring, then fruitful summer, followed by autumn.

3.2 Star Year

Comparing the view of the starry sky immediately after sunset from day to day for several weeks, it can be seen 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 stellar ocean, astronomers have divided the sky into 88 separate areas - constellations. The sun passes through 12 constellations, which are called zodiacal, throughout the year.

In the past, about 2000 years ago, and in the Middle Ages, for convenience in reading the position of the Sun on the ecliptic, it was divided into 12 equal parts, 30 ° each. It was customary to designate each arc of 30 ° by the sign of the zodiacal constellation through which the Sun passed in one month or another. This is how the "signs of the zodiac" appeared in the sky. The point of the vernal equinox, located at the beginning of AD, was taken as the starting point. e. in the constellation Aries. The arc of 30 ° measured from it was designated by the sign “ram's horns”. Further, the Sun passed through the constellation Taurus, therefore 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", that is, in fact, at certain angular distances from the point of spring equinoxes have been carried out for centuries to draw up horoscopes.

3.4 Typical Star Rises and Sets

Due to the continuous movement of the disk of the Sun in the celestial sphere from west to east, the view of the starry sky from evening to evening, albeit slowly, but continuously changes. So, if at a certain time of the year some constellation of the zodiac is visible in the southern part of the sky an hour after sunset (say, 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 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 zodiacal constellation will already disappear in the rays of the evening dawn, and after 10-20 days it will be visible in the morning before sunrise in the eastern part of the sky. Other setting constellations and individual stars behave in approximately 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 star, 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 dawn (ie, the first morning sunrise) 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, already passes the meridian (at 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 dawn, which occurs only once a year (morning sunset), is usually called a cosmic ("space" - "decoration") sunset. Further, the rising of a star above the horizon in the east at sunset (rising in the rays of the evening dawn) is called its acronical rise (from the Greek "acros" - the highest; apparently, the position farthest from the Sun was meant). And, finally, the setting of a star in the rays of 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, moving from the southern hemisphere of the celestial sphere to the northern one. The point of intersection of the celestial equator with the ecliptic - 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 average sun also returns to the vernal equinox in the same time.

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

3.6 Precession

The duration of 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 is called precession, or anticipation of the equinoxes. For 72 years, the vernal equinox shifts along the ecliptic by 1 ?, for 1000 years - by 14 °, etc. In about 26,000 years it will make a full circle on the celestial sphere. In the past, about 4000 years ago, the vernal equinox point was in the constellation Taurus not far from the Pleiades star cluster, while the summer solstice at this time occurred at the time of the passage of the Sun through the constellation Leo near the star Regulus.

The phenomenon of precession arises because the shape of the Earth differs 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 poles of the world move among the stars in small circles with radii of about 23 ° 27 /. At the same time, the entire grid of equatorial coordinates is shifted on the celestial sphere, and from it the point of the vernal equinox. Due to the precession, the appearance of the starry sky on a certain day of the year changes slowly but continuously.

3.7 Changing the number of days in a year

Observations of stellar climaxes carried out over many decades have shown that 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 seemingly negligible 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 of 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 on its axis per year.

4 CHANGE OF THE MOON PHASES

Probably the first of the astronomical phenomena to which primitive man drew attention was the change in the phases of the moon. It was she who allowed him to learn how to keep track of the day. And it is no coincidence that in many languages \u200b\u200bthe word "month" has a common root, consonant with the roots of the words "measure" and "Moon", for example, Latin mensis - month and mensurа - measure, Greek "mene" - Moon and "Maine" - month , English moon - Moon and month - month. And the Russian national name for 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 make sure 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. Therefore, we can say that for every day the Moon shifts 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 in the celestial sphere, the Moon after 27.321661 days (\u003d 27d07h43mlls, 5) returns to the same star. This period of time is called the sidereal (i.e., stellar: sidus - star in Latin) month.

4.2 Moon configurations and phases

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 moon's surface is cold and glows with reflected sunlight. When the Moon revolves around the Earth or, as they say, when changing the configuration of the Moon (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 differently. The consequence of this is the periodic change in the phases of the moon. When the Moon, in its motion, is between the Sun and the Earth (this position is called conjunction - conjunction), it faces the Earth with its unlit side, and then it is not visible at all. This is the 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 more days, the Moon occupies a position directly opposite to the Sun and its side facing the Earth is completely illuminated by it. The full moon comes, at which time the moon rises at sunset and is visible in the sky all night. 7 days after the full moon, the last quarter occurs, when the moon is again visible in the form of a semicircle, with its bulge turned in the other direction, and rises after midnight. Recall that if at the time of the new moon the moon's shadow falls on the Earth (more often it slips "above" or "below" our planet), a solar eclipse occurs. If the Moon in the full moon plunges into 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 a synodic month. It is equal to 29.53058812 days \u003d 29d12h44m2s, 8. The twelve synodic months are 354.36706 days. Thus, the synodic month is incommensurable neither with the days, nor with the tropical year: it does not consist of a whole number of days and does not fit without a remainder in a 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 changed its phases, and divide the first value by the second (moreover, select several pairs and find mean). Since the Moon moves around the Earth in an elliptical orbit, the linear and observed angular velocities of its motion 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 and the force of gravity acting on it from the Sun is very complicated, because the magnitude of this force is constantly changing both in its numerical value and in direction: it has the greatest value in the new moon and the smallest in the full moon. The real length 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 kept track of the days of "eight days" - trading weeks, in which the days were designated by letters from A to H; seven days of this week were working days, the eighth - bazaar. These market days also became festival days.

The custom of measuring the time of 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 a full moon, etc.

But observations of the starry sky gave one more confirmation of the "exceptionalism" of the number seven. At one time, ancient Babylonian astronomers discovered that, in addition to fixed stars, seven "wandering" luminaries are also visible in the sky, which were later called planets (from the Greek word "planethes", which means "wandering"). It was assumed that these luminaries revolve around the Earth and that their distances from it increase in the following order: Moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn. Astrology arose in Ancient Babylon - the belief that the planets influence the fate of individuals and entire nations. Comparing certain events in the life of people with the position of the planets in the starry sky, astrologers believed that the same event would occur again if this arrangement of the stars 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 days of the week

Dividing the day into 24 hours, the ancient Babylonian astrologers made 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: its 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 at the hour of the next day, Sunday, the Sun "ruled", the first hour of the third day was the Moon, the fourth by Mars, the fifth by Mercury, the sixth by Jupiter and the seventh by 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 symbols were usually placed (Figure 00).

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

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

In Russian, the name of the day passed on to the entire seven-day period (week, as it was once called). Thus, 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 Church Slavonic language there is also an older name - the third.

In conclusion, it should be noted that the seven-day week spread in the Roman Empire during the reign of Emperor Augustus (63 BC - 14 AD) in connection with the fascination of the Romans with astrology. In particular, wall paintings of the seven gods of the days of the week were found in Pompeii. The very widespread and "survivability" of a time interval of seven days is apparently associated with the presence of certain psychophysiological rhythms of the human body of the corresponding duration.

6 ARITHMETICS 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 in the 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 - the synodic month andtropical year - contain fractional parts of a day. “Therefore,” says the renowned expert on the “calendar problem” Leningrad professor NI Idelson (1885-1951), “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 can these discrepancies be corrected? This is a purely arithmetic task; 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 After the duration of the tropical year and synodic month is reliably established with the help of astronomical observations, and the rules of alternation are obtained from the theory of numbers 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 NI Idelson, the calendar system "gets its course, as it were, independently of astronomy" and, "turning to the calendar, we should not at all ... focus on those astronomical facts and relationships from which it is derived." And vice versa: "A calendar that remains in constant contact with astronomy becomes cumbersome and inconvenient."

6.1 Lunar calendar

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

12X29.53059 \u003d 354.36706 days.

Therefore, it can be assumed that the calendar lunar year consists of 354 days: of six "full" months of 30 days and six "empty" months of 29 days, since 6 X 30 + 6 X 29 \u003d 354. And so that the beginning of the calendar month as possible more precisely coincided with the new moon, these months should alternate; for example, all odd months can contain 30 days, and even ones 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 \u003d 1.10118 days. Consequently, in the fourth year from the beginning of the count, the new moons will no longer fall 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 insert in one day, that is, 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 reduced to the following: to find such an order of alternation of simple and leap lunar years, in which the beginning of the calendar months would not noticeably move away from the new moon.

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

6.2 Lunar-solar calendar

Theory. The theory of the lunisolar calendar of Rey is based on two astronomical quantities:

1 tropical year \u003d 365.242 20 days;

1 synodic month \u003d 29.530 59 days.

From here we get:

1 tropical year \u003d 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 embolismic(from the Greek "embolismos" - insert).

Note that in Ancient Rome and medieval Europe, the insertion of an additional day or month was usually called intercalation (from the Latin intercalatio - insert), and the added month itself was called an 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 duration of the tropical year. The 13th month is inserted from time to time so that the beginning of the calendar year is kept as close as possible to some moment of the astronomical solar year, for example, to the equinox.

6.3 Solar calendar

The solar calendar is based on the duration of the tropical year - 365.24220 days. From this it is immediately clear that a calendar year can contain either 365 or 366 days. The theory should indicate the order of alternation of simple (365 days) and leap (366 days) years in a certain cycle so that the average length of a calendar year per cycle is as close as possible to the duration of a tropical year.

Thus, the cycle is four years long and one insertion is made during this cycle. In other words, out of every four years, three years have 365 days, the fourth has 366 days. Such a leap system 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 in about 128 years is a whole day.

Since 1582, the countries of Western Europe, and later many other peoples of the world, switched to the time according to the Gregorian calendar, the project of which was developed by the Italian scientist Luigi Lilio (1520-1576). The length of the calendar year is taken here equal to 365.24250 days. In accordance with the value of the fractional part of the year / (\u003d 0.2425 \u003d 97/400 in a time interval of 400 years, an additional 366th day in a year is inserted 97 times, i.e., compared with the Julian calendar, three days in 400 years are thrown out here ...

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

The insertion of the additional 366th day of the year should be done 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 as leap years those secular years in which the number of hundreds when divided by 9 gives the remainder of 2 or 6. The nearest such years, starting from 2000, will be 2400, 2900, 3300 and 3800. The average length of the New Julian calendar year is longer than the length of the year. tropical by 0.000022 average solar days. This means that such a calendar gives a discrepancy in 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 ordinal number in our chronology is divisible by 4 without a remainder. In this case, however, those secular years of the calendar, the number of hundreds of which is not evenly divisible by 4, are considered simple (for example, 1500, 1700, 1800, 1900, etc.). Leap centuries are 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, on 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. Consequently, in terms of the accuracy and clarity of the leap system (which makes it easier to memorize), 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, 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 time period is the day, determined 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 calculating large periods of time, a day is of little use, a large unit is needed. These were the period when the phases of the moon changed - a month, and the period when the seasons changed - 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, came to be called 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

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3. Dunichev V.M. Concepts of modern natural science: Study guide / Dunichev V.M. - Yuzhno-Sakhalinsk: Sakhalin Book Publishing House, 2000. - 124 p.

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

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