The rotation of the Earth around its axis and the Sun occurs continuously. Many phenomena depend on this movement. So, day gives way to night, one season to another, different climates are established in different areas.

The daily rotation of the Earth, according to scientists, is 23 hours, 56 minutes, 4.09 seconds. Thus, one full revolution occurs. At a speed of approximately 1,670 km/h, the planet moves around its axis. Toward the poles, the speed decreases to zero.

A person does not notice the rotation due to the fact that all objects located next to him move simultaneously and in parallel at the same speed.

Carried out in orbit. It is located on an imaginary surface passing through the center of our planet and This surface is called the orbital plane.

An imaginary line between the poles passes through the center of the Earth - the axis. This line and the orbital plane are not perpendicular. The axis tilt is approximately 23.5 degrees. The angle of inclination always remains the same. The line around which the Earth moves is always inclined in one direction.

It takes the planet a year to move around its orbit. In this case, the Earth rotates counterclockwise. It should be noted that the orbit is not perfectly circular. The average distance to the Sun is about one hundred and fifty million kilometers. It (the distance) varies by an average of three million kilometers, thus forming a slight orbital oval.

The Earth's orbital revolution is 957 million km. The planet covers this distance in three hundred and sixty-five days, six hours, nine minutes and nine and a half seconds. According to calculations, the Earth rotates in orbit at a speed of 29 kilometers per second.

Scientists have found that the planet's movement is slowing down. This is mainly due to tidal braking. On the surface of the Earth, under the influence of the attraction of the Moon (to a greater extent) and the Sun, tidal shafts are formed. They move from east to west (following these in the opposite direction to the movement of our planet.

Less importance is attached to tides in the Earth's lithosphere. In this case, the solid body is deformed in the form of a slightly delayed tidal wave. It provokes the occurrence of a braking torque, which helps slow down the rotation of the Earth.

It should be noted that tides in the lithosphere affect the process of deceleration of the planet by only 3%, the remaining 97% is due to sea tides. This data was obtained by creating wave maps of lunar and solar tides.

Atmospheric circulation also affects the speed of the Earth. It is considered the main cause of the seasonal uneven atmosphere occurring from east to west in low latitudes, and from west to east in high and temperate latitudes. At the same time, the western winds have a positive angular momentum, while the eastern winds have a negative angular momentum and, according to calculations, several times less than the former. This difference is redistributed between the Earth and the atmosphere. When the westerly wind strengthens or the eastern wind weakens, it increases near the atmosphere and decreases near the Earth. Thus, the movement of the planet slows down. With the strengthening of eastern winds and the weakening of western winds, the angular momentum of the atmosphere decreases accordingly. Thus, the Earth's movement becomes faster. The total angular momentum of the atmosphere and planet is a constant value.

Scientists were able to find out that the lengthening of the day before 1620 occurred on average by 2.4 milliseconds per hundred years. After this year, the value decreased by almost half and became 1.4 milliseconds per hundred years. Moreover, according to some recent calculations and observations, the Earth is slowing down by an average of 2.25 milliseconds per hundred years.

Like all the planets of our vast solar system, the Earth makes two main revolutions - around its axis and around the Sun. The time of one rotation of the Earth around its axis is called a day, and the period during which it circles its orbit around the Sun is called a year. This movement is the key to life and physical laws on the planet, according to which we all exist. At the slightest failure (which has not happened yet), the work of all spheres of the Earth, ecosystems and living organisms will be disrupted.

Features of the planet's rotation

Both in the people and in science, the time of one rotation of the Earth around its axis is called a day. They consist of day and night, which last on average 24 hours. Our planet rotates counterclockwise, that is, from west to east. It is thanks to this that residents of the eastern regions are the first to greet the dawn, and the inhabitants of the western hemisphere are the last. An axis is a conventional line that passes through the south and north poles of the planet. Thus, these extreme points do not participate in the rotation process, while all other parts of the earth move.

Since the planet moves from west to east, we can observe how the entire celestial sphere seems to pass by us in the opposite direction, that is, from east to west. This applies to both the Sun and all the stars that we have. The exception is the Moon, since it is an earthly satellite that has an individual orbit.

The movement of our planet in numbers

It is the daily period that determines the speed around the axis. In 24 hours, this celestial body must complete its revolution, taking into account its own parameters and mass. We have already said that the axis permeates the Earth from north to south, and during this process the poles do not rotate around it. At this time, all other zones, including the circumpolar and equatorial ones, move at a certain pace. The speed of rotation of the Earth near the equator is maximum. It reaches 1670 km/h. Moreover, in this area, day and night have an equal number of hours throughout the year.

The Earth's rotation speed in Italy reaches an average of 1200 km/h with a seasonal change in the length of day and night. Thus, the closer we move to the poles, the slower the planet rotates there, gradually coming to zero.

What types of days are there and how are they calculated?

The time of one rotation of the Earth around its axis is called a day, and exactly 24 hours are placed in this interval. But it is worth remembering that there are such concepts as solar days and sidereal days, which have a small but significant difference.

First, let's look at all the features of the first type. Firstly, not every day lasts exactly 24 hours. At those moments when the planet approaches the Sun, its speed of rotation around its axis increases. During periods of distance from the main body of the system, the movement of planet Earth slows down. Therefore, in summer the days may pass a little faster, and in winter they last longer.

As for the sidereal day, its duration is 23 hours, 56 minutes and 4 seconds. This is the time during which our planet rotates around its axis relative to some distant star. That is, if the distant luminary turned out to be the Sun, then the entire rotation, consisting of 360 degrees, would be complete during this period. Well, in order for it to reach the end relative to the Sun itself, it is necessary to go one more degree, which takes just four minutes.

The second important rotation of the planet is around the Sun

The Earth circles the Sun in an elliptical orbit. That is, its circulation occurs not in a clear circle shape, but in an oval pattern. The speed of the Earth around the Sun is on average 107,000 km/h, but this unit is not constant. The average distance of our planet from the sun is 150 million kilometers. An accurate and unchangeable unit is the degree of inclination of the earth's axis relative to the orbit - 66 degrees and 33 seconds, regardless of the time of day or year. It is this inclination, coupled with the shape of the orbit, the variable speed of movement and circulation, that gives us the opportunity to feel seasonal climate changes, but not in all latitudes. If daily fluctuations in time and any changes are multiplied by zero near the poles, then seasonal features also freeze at the equator. Every day from year to year here passes the same way as the previous one, with the same weather, as well as the length of day and night.

The ecliptic and its annual cycle

The term “ecliptic” means a section of the celestial sphere that is within the limits of the Moon. Within the boundaries of this conventional circle, all the main movements of our planet occur, as well as the revolution of the Moon around it. It is worth noting that the latter has a significant influence on the climate, the hydrosphere, and the Moon can be the cause of eclipses, lithospheric metamorphoses and much more.

As for the ecliptic itself, this plane has its own celestial equator, which has certain astronomical coordinates. The inclination of all planets in the solar system is calculated relative to them. The position of the stars and galaxies that we see in the sky is calculated in a similar way (after all, their light falls on the ecliptic, therefore, all those viewed are part of it). This theory is the basis of astrology. According to this science, those constellations that pass through the ecliptic make up the Zodiac. The only unit that does not fall into this category is Ophiuchus. This constellation is visible in the sky, but it is not in the astrological tables.

Summing up

We have determined that the time of one revolution of the Earth around its axis is called a day. The latter are solar (24 hours) or sidereal (23 hours 56 minutes). The change of day and night occurs in all latitudes of the planet with the exception of the poles. There the earth's rotation speed is zero. The planet's revolution around the Sun occurs every year - 365 days. During this period, there is a change of seasons in all corners of the Earth, but not at the equator. This zone is the most stable, while it rotates around its axis with

Rotation of the Earth around its axis

The rotation of the Earth is one of the movements of the Earth, which reflects many astronomical and geophysical phenomena occurring on the surface of the Earth, in its interior, in the atmosphere and oceans, as well as in near space.

The rotation of the Earth explains the change of day and night, the apparent daily movement of celestial bodies, the rotation of the swing plane of a load suspended on a thread, the deflection of falling bodies to the east, etc. Due to the rotation of the Earth, the Coriolis force acts on bodies moving on its surface, the influence of which is manifested in the erosion of the right banks of rivers in the Northern Hemisphere and the left ones in the Southern Hemisphere of the Earth and in some features of atmospheric circulation. The centrifugal force generated by the Earth's rotation partly explains the differences in the acceleration of gravity at the equator and the Earth's poles.

To study the patterns of Earth's rotation, two coordinate systems are introduced with a common origin at the Earth's center of mass (Fig. 1.26). The earth's system X 1 Y 1 Z 1 participates in the daily rotation of the Earth and remains motionless relative to points on the earth's surface. The XYZ stellar coordinate system is not related to the Earth's daily rotation. Although its origin moves in cosmic space with some acceleration, participating in the annual motion of the Earth around the Sun in the Galaxy, this motion of relatively distant stars can be considered uniform and rectilinear. Therefore, the motion of the Earth in this system (as well as any celestial object) can be studied according to the laws of mechanics for an inertial reference frame. The XOY plane is aligned with the ecliptic plane, and the X axis is directed to the vernal equinox point γ of the initial epoch. It is convenient to take the main axes of inertia of the Earth as the axes of the earth's coordinate system; another choice of axes is possible. The position of the earth's system relative to the stellar system is usually determined by three Euler angles ψ, υ, φ.

Fig.1.26. Coordinate systems used to study the rotation of the Earth

Basic information about the rotation of the Earth comes from observations of the daily movement of celestial bodies. The rotation of the Earth occurs from west to east, i.e. counterclockwise as seen from the Earth's North Pole.

The average inclination of the equator to the ecliptic of the initial era (angle υ) is almost constant (in 1900 it was equal to 23° 27¢ 08.26² and during the 20th century it increased by less than 0.1²). The line of intersection of the Earth's equator and the ecliptic of the initial epoch (line of nodes) slowly moves along the ecliptic from east to west, moving by 1° 13¢ 57.08² per century, as a result of which the angle ψ changes by 360° in 25,800 years (precession). The instantaneous axis of rotation of the OR always almost coincides with the smallest axis of inertia of the Earth. According to observations made since the end of the 19th century, the angle between these axes does not exceed 0.4².

The period of time during which the Earth makes one revolution around its axis relative to some point in the sky is called a day. Points that determine the length of the day can be:

· point of vernal equinox;

· the center of the visible disk of the Sun, displaced by annual aberration (“true Sun”);

· “average Sun” is a fictitious point, the position of which in the sky can be calculated theoretically for any moment in time.

The three different periods of time defined by these points are called sidereal, true solar and average solar days, respectively.

The speed of rotation of the Earth is characterized by the relative value

where P z is the duration of an earthly day, T is the duration of a standard day (atomic), which is equal to 86400 s;

- angular velocities corresponding to terrestrial and standard days.

Since the value of ω changes only in the ninth – eighth digit, the values of ν are of the order of 10 -9 -10 -8.

The Earth makes one full revolution around its axis relative to the stars in a shorter period of time than relative to the Sun, since the Sun moves along the ecliptic in the same direction in which the Earth rotates.

The sidereal day is determined by the period of rotation of the Earth around its axis in relation to any star, but since the stars have their own and, moreover, very complex movement, it was agreed that the beginning of the sidereal day should be counted from the moment of the upper culmination of the vernal equinox, and the length of the sidereal day is taken to be the interval the time between two successive upper culminations of the vernal equinox located on the same meridian.

Due to the phenomena of precession and nutation, the relative position of the celestial equator and the ecliptic continuously changes, which means that the location of the vernal equinox on the ecliptic changes accordingly. It has been established that the sidereal day is 0.0084 seconds shorter than the actual period of the Earth's daily rotation and that the Sun, moving along the ecliptic, reaches the vernal equinox point earlier than it reaches the same place relative to the stars.

The Earth, in turn, revolves around the Sun not in a circle, but in an ellipse, so the movement of the Sun seems uneven to us from the Earth. In winter, true solar days are longer than in summer. For example, at the end of December they are 24 hours 04 minutes 27 seconds, and in mid-September they are 24 hours 03 minutes. 36sec. The average unit of solar day is considered to be 24 hours 03 minutes. 56.5554 sec sidereal time.

Due to the ellipticity of the Earth's orbit, the angular velocity of the Earth relative to the Sun depends on the time of year. The Earth moves slowest in its orbit when it is at perihelion - the point of its orbit farthest from the Sun. As a result, the duration of the true solar day is not the same throughout the year - the ellipticity of the orbit changes the duration of the true solar day according to a law that can be described by a sinusoid with an amplitude of 7.6 minutes. and a period of 1 year.

The second reason for the unevenness of the day is the inclination of the earth's axis to the ecliptic, leading to the apparent movement of the Sun up and down from the equator throughout the year. The direct ascension of the Sun near the equinoxes (Fig. 1.17) changes more slowly (since the Sun moves at an angle to the equator) than during the solstices, when it moves parallel to the equator. As a result, a sinusoidal term with an amplitude of 9.8 minutes is added to the duration of the true solar day. and a period of six months. There are other periodic effects that change the length of the true solar day and depend on time, but they are small.

As a result of the combined action of these effects, the shortest true solar days are observed on March 26-27 and September 12-13, and the longest on June 18-19 and December 20-21.

To eliminate this variability, they use the average solar day, tied to the so-called average Sun - a conditional point moving uniformly along the celestial equator, and not along the ecliptic, like the real Sun, and coinciding with the center of the Sun at the moment of the vernal equinox. The period of revolution of the average Sun across the celestial sphere is equal to a tropical year.

The average solar day is not subject to periodic changes, like the true solar day, but its duration changes monotonically due to changes in the period of the Earth's axial rotation and (to a lesser extent) with changes in the length of the tropical year, increasing by approximately 0.0017 seconds per century. Thus, the duration of the average solar day at the beginning of 2000 was equal to 86400.002 SI seconds (the SI second is determined using the intra-atomic periodic process).

A sidereal day is 365.2422/366.2422=0.997270 average solar day. This value is the constant ratio of sidereal and solar time.

Mean solar time and sidereal time are related to each other by the following relationships:

24 hours Wed. solar time = 24 hours. 03 min. 56.555sec. sidereal time

1 hour = 1h. 00 min. 09.856 sec.

1 min. = 1 min. 00.164 sec.

1 sec. = 1.003 sec.

24 hours sidereal time = 23 hours 56 minutes. 04.091 sec. Wed solar time

1 hour = 59 minutes 50.170 sec.

1 min. = 59.836 sec.

1 sec. = 0.997 sec.

Time in any dimension - sidereal, true solar or average solar - is different on different meridians. But all points lying on the same meridian at the same moment in time have the same time, which is called local time. When moving along the same parallel to the west or east, the time at the starting point will not correspond to the local time of all other geographical points located on this parallel.

In order to eliminate this drawback to some extent, the Canadian S. Flushing proposed introducing standard time, i.e. a time counting system based on dividing the Earth's surface into 24 time zones, each of which is 15° in longitude from the neighboring zone. Flushing put 24 main meridians on the world map. Approximately 7.5° to the east and west of them, the boundaries of the time zone of this zone were conventionally drawn. The time of the same time zone at each moment for all its points was considered the same.

Before Flushing, maps with different prime meridians were published in many countries around the world. So, for example, in Russia longitudes were counted from the meridian passing through the Pulkovo Observatory, in France - through the Paris Observatory, in Germany - through the Berlin Observatory, in Turkey - through the Istanbul Observatory. To introduce standard time, it was necessary to unify a single prime meridian.

Standard time was first introduced in the United States in 1883, and in 1884. In Washington, at the International Conference, in which Russia also took part, an agreed decision was made on standard time. The conference participants agreed to consider the prime or prime meridian to be the meridian of the Greenwich Observatory, and the local mean solar time of the Greenwich meridian was called universal or world time. The so-called “date line” was also established at the conference.

In our country, standard time was introduced in 1919. Taking as a basis the international system of time zones and the administrative boundaries that existed at that time, time zones from II to XII inclusive were applied to the map of the RSFSR. The local time of time zones located east of the Greenwich meridian increases by an hour from zone to zone, and correspondingly decreases by an hour to the west of Greenwich.

When calculating time by calendar days, it is important to establish on which meridian the new date (day of the month) begins. According to international agreement, the date line runs for the most part along the meridian, which is 180° away from Greenwich, retreating from it: to the west - near Wrangel Island and the Aleutian Islands, to the east - off the coast of Asia, the islands of Fiji, Samoa, Tongatabu, Kermandek and Chatham.

To the west of the date line, the day of the month is always one more than to the east of it. Therefore, after crossing this line from west to east, it is necessary to reduce the number of the month by one, and after crossing it from east to west, increase it by one. This date change is usually made at the nearest midnight after crossing the International Date Line. It is quite obvious that a new calendar month and a new year begin on the International Date Line.

Thus, the prime meridian and the 180°E meridian, along which the date line mainly passes, divide the globe into the western and eastern hemispheres.

Throughout the history of mankind, the daily rotation of the Earth has always served as an ideal standard of time, which regulated the activities of people and was a symbol of uniformity and accuracy.

The oldest tool for determining time BC was a gnomon, a pointer in Greek, a vertical pillar on a leveled area, the shadow of which, changing its direction as the Sun moved, showed this or that time of day on a scale marked on the ground near the pillar. Sundials have been known since the 7th century BC. Initially, they were common in Egypt and the countries of the Middle East, from where they moved to Greece and Rome, and even later penetrated into the countries of Western and Eastern Europe. Astronomers and mathematicians of the ancient world, the Middle Ages and modern times dealt with issues of gnomonics - the art of making sundials and the ability to use them. In the 18th century and at the beginning of the 19th century. Gnomonics was presented in mathematics textbooks.

And only after 1955, when the demands of physicists and astronomers for time accuracy increased greatly, it became impossible to be satisfied with the daily rotation of the Earth as a standard of time, which was already uneven with the required accuracy. Time, determined by the rotation of the Earth, is uneven due to the movements of the pole and the redistribution of angular momentum between different parts of the Earth (hydrosphere, mantle, liquid core). The meridian adopted for timing is determined by the EOR point and the point on the equator corresponding to zero longitude. This meridian is very close to Greenwich.

The earth rotates unevenly, which causes changes in the length of the day. The speed of the Earth's rotation can most simply be characterized by the deviation of the duration of the Earth's day from the standard (86,400 s). The shorter the Earth's day, the faster the Earth rotates.

There are three components in the magnitude of changes in the Earth's rotation speed: secular slowdown, periodic seasonal fluctuations and irregular abrupt changes.

The secular slowdown in the speed of rotation of the Earth is caused by the tidal forces of attraction of the Moon and the Sun. The tidal force stretches the Earth along a straight line connecting its center with the center of the disturbing body - the Moon or the Sun. In this case, the compression force of the Earth increases if the resultant coincides with the equatorial plane, and decreases when it deviates towards the tropics. The moment of inertia of the compressed Earth is greater than that of an undeformed spherical planet, and since the angular momentum of the Earth (i.e., the product of its moment of inertia by the angular velocity) must remain constant, the rotation speed of the compressed Earth is less than that of the undeformed Earth. Due to the fact that the declinations of the Moon and the Sun, the distances from the Earth to the Moon and the Sun are constantly changing, the tidal force fluctuates over time. The Earth's compression changes accordingly, which ultimately causes tidal fluctuations in the Earth's rotation speed. The most significant of them are fluctuations with semi-monthly and monthly periods.

The slowdown in the Earth's rotation rate is detected during astronomical observations and paleontological studies. Observations of ancient solar eclipses led to the conclusion that the length of the day increases by 2 seconds every 100,000 years. Paleontological observations of corals have shown that corals of warm seas grow, forming a belt, the thickness of which depends on the amount of light received per day. Thus, it is possible to determine the annual changes in their structure and calculate the number of days in a year. In the modern era, 365 coral belts have been found. According to paleontological observations (Table 5), the length of the day increases linearly with time by 1.9 s per 100,000 years.

Table 5

According to observations over the past 250 years, the day has increased by 0.0014 s per century. According to some data, in addition to tidal slowdown, there is an increase in the rotation speed by 0.001 s per century, which is caused by a change in the moment of inertia of the Earth due to the slow movement of matter inside the Earth and on its surface. Its own acceleration reduces the length of the day. Consequently, if it were not there, then the day would increase by 0.0024 s per century.

Before the creation of atomic clocks, the rotation of the Earth was controlled by comparing the observed and calculated coordinates of the Moon, Sun and planets. In this way, it was possible to obtain an idea of the change in the speed of rotation of the Earth over the last three centuries - from the end of the 17th century, when the first instrumental observations of the movement of the Moon, Sun and planets began. Analysis of these data shows (Fig. 1.27) that from the beginning of the 17th century. until the middle of the 19th century. The Earth's rotation speed changed little. From the second half of the 19th century. To date, significant irregular velocity fluctuations have been observed with characteristic times of the order of 60-70 years.

Fig.1.27. Deviation of day length from standard values over 350 years

The Earth rotated most quickly around 1870, when the length of the Earth's day was 0.003 s shorter than the standard. The slowest - around 1903, when the earth's day was 0.004 s longer than the standard one. From 1903 to 1934 There was an acceleration of the Earth's rotation from the late 30s to 1972. there was a slowdown, and since 1973. Currently, the Earth is accelerating its rotation.

Periodic annual and semi-annual fluctuations in the Earth's rotation rate are explained by periodic changes in the Earth's moment of inertia due to the seasonal dynamics of the atmosphere and the planetary distribution of precipitation. According to modern data, the length of the day changes by ±0.001 seconds throughout the year. The shortest days are in July-August, and the longest days are in March.

Periodic changes in the speed of rotation of the Earth have periods of 14 and 28 days (lunar) and 6 months and 1 year (solar). The minimum speed of the Earth's rotation (acceleration is zero) corresponds to February 14, the average speed (maximum acceleration) is May 28, the maximum speed (acceleration is zero) is August 9, the average speed (minimum deceleration) is November 6.

Random changes in the speed of rotation of the Earth are also observed, which occur at irregular intervals of time, almost multiples of eleven years. The absolute value of the relative change in angular velocity reached in 1898. 3.9×10 -8, and in 1920 – 4.5×10 -8. The nature and nature of random fluctuations in the Earth's rotation speed have been little studied. One hypothesis explains the irregular fluctuations in the angular velocity of the Earth's rotation by the recrystallization of some rocks inside the Earth, changing its moment of inertia.

Before the discovery of the uneven rotation of the Earth, the derived unit of time - the second - was defined as 1/86400 of the average solar day. The variability of the average solar day due to the uneven rotation of the Earth forced us to abandon this definition of the second.

In October 1959 The International Bureau of Weights and Measures has decided to give the following definition to the fundamental unit of time, the second:

"A second is 1/31556925.9747 of the tropical year for 1900, January 0, at 12 o'clock ephemeris time."

The second defined in this way is called “ephemeris”. The number 31556925.9747=86400´365.2421988 is the number of seconds in the tropical year, the duration of which for the year 1900, January 0, at 12 hours of ephemeris time (uniform Newtonian time) was equal to 365.2421988 average solar days.

In other words, an ephemeris second is a period of time equal to 1/86400 of the average length of the average solar day, which they had in 1900, in January 0, at 12 hours of ephemeris time. Thus, the new definition of the second was also associated with the movement of the Earth around the Sun, while the old definition was based only on its rotation around its axis.

Nowadays, time is a physical quantity that can be measured with the highest accuracy. The unit of time - the second of "atomic" time (SI second) - is equal to the duration of 9192631770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom, was introduced in 1967 by the decision of the XII General Conference of Weights and Measures, and in 1970 " atomic" time was taken as the fundamental reference time. The relative accuracy of the cesium frequency standard is 10 -10 -10 -11 over several years. The atomic time standard has neither daily nor secular fluctuations, does not age and has sufficient certainty, accuracy and reproducibility.

With the introduction of atomic time, the accuracy of determining the unevenness of the Earth's rotation has significantly improved. From this moment on, it became possible to record all fluctuations in the Earth's rotation speed with a period of more than one month. Figure 1.28 shows the course of average monthly deviations for the period 1955-2000.

From 1956 to 1961 The Earth's rotation accelerated from 1962 to 1972. - slowed down, and since 1973. to the present – it has accelerated again. This acceleration has not yet ended and will continue until 2010. Rotation acceleration 1958-1961 and slowdown 1989-1994. are short-term fluctuations. Seasonal variations cause the Earth's rotation speed to be slowest in April and November, and highest in January and July. The January maximum is significantly less than the July maximum. The difference between the minimum deviation of the duration of the earth's day from the standard in July and the maximum in April or November is 0.001 s.

Fig.1.28. Average monthly deviations of the duration of the Earth's day from the standard for 45 years

The study of the unevenness of the Earth's rotation, nutation of the Earth's axis and the movement of the poles is of great scientific and practical importance. Knowledge of these parameters is necessary to determine the coordinates of celestial and terrestrial objects. They contribute to expanding our knowledge in various fields of geosciences.

In the 80s of the 20th century, new methods of geodesy replaced astronomical methods for determining the parameters of the Earth's rotation. Doppler observations of satellites, laser ranging of the Moon and satellites, GPS global positioning system, radio interferometry are effective means for studying the uneven rotation of the Earth and the movement of the poles. The most suitable for radio interferometry are quasars - powerful sources of radio emission of extremely small angular size (less than 0.02²), which are, apparently, the most distant objects of the Universe, practically motionless in the sky. Quasar radio interferometry represents the most effective and independent of optical measurements means for studying the rotational motion of the Earth.

The earth is spherical, however, it is not a perfect sphere. Due to rotation, the planet is slightly flattened at the poles; such a figure is usually called a spheroid or geoid - “like the earth.”

The earth is huge, its size is difficult to imagine. The main parameters of our planet are as follows:

Diameter - 12570 km
Length of the equator - 40076 km
The length of any meridian is 40008 km
The total surface area of the Earth is 510 million km2
Radius of the poles - 6357 km
Equator radius - 6378 km

The earth simultaneously rotates around the sun and around its own axis.

What types of Earth motion do you know?
Annual and daily rotation of the Earth

Rotation of the Earth around its axis

The earth rotates around an inclined axis from west to east.

Half of the globe is illuminated by the sun, it is day there at that time, the other half is in the shadow, there it is night. Due to the rotation of the Earth, the cycle of day and night occurs. The Earth makes one revolution around its axis in 24 hours - a day.

Due to rotation, moving currents (rivers, winds) are deflected to the right in the northern hemisphere, and to the left in the southern hemisphere.

Rotation of the Earth around the Sun

The Earth rotates around the sun in a circular orbit, completing a full revolution in 1 year. The earth's axis is not vertical, it is inclined at an angle of 66.5° to the orbit, this angle remains constant during the entire rotation. The main consequence of this rotation is the change of seasons.

Let's consider the extreme points of the Earth's rotation around the Sun.

December 22- winter solstice day. The southern tropic is closest to the sun (the sun is at its zenith) at this moment - therefore, it is summer in the southern hemisphere, and winter in the northern hemisphere. Nights in the southern hemisphere are short; on December 22, in the southern polar circle, the day lasts 24 hours, night does not come. In the northern hemisphere, everything is the other way around; in the Arctic Circle, the night lasts 24 hours.
June 22- day of the summer solstice. The northern tropic is closest to the sun; it is summer in the northern hemisphere and winter in the southern hemisphere. In the southern polar circle, night lasts 24 hours, but in the northern circle there is no night at all.
March 21, September 23- days of the spring and autumn equinoxes The equator is closest to the sun; day is equal to night in both hemispheres.

Rotation of the Earth around its axis and around the Sun Shape and dimensions of the Earth Wikipedia
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Year

Time one revolution Earth around Sun . In the process of annual movement, our planet moves in space with an average speed of 29.765 km/s, i.e. more than 100,000 km/h.

anomalistic

An anomalistic year is the period time between two consecutive passes Earth his perihelion . Its duration is 365.25964 days . It's about 27 minutes longer than the running time tropical(see here) years. This is caused by the continuous change in the position of the perihelion point. In the current time period, the Earth passes the perihelion point on January 2nd

leap year

Every fourth year as currently used in most countries of the world calendar has an extra day - February 29 - and is called a leap day. The need for its introduction is due to the fact that Earth makes one revolution around Sun for a period not equal to a whole number days . The annual error is equal to almost a quarter of a day and every four years it is compensated by the introduction of an “extra day”. See also Gregorian calendar .

sidereal (stellar)

Time turnover Earth around Sun in the coordinate system of “fixed stars ”, i.e., as if “when looking at solar system from the outside." In 1950 it was equal to 365 days , 6 hours, 9 minutes, 9 seconds.

Under the disturbing influence of the attraction of others planets , mainly Jupiter And Saturn , the length of the year is subject to fluctuations of several minutes.

In addition, the length of the year decreases by 0.53 seconds per hundred years. This occurs because the Earth, by tidal forces, slows down the rotation of the Sun around its axis (see Fig. Ebbs and flows ). However, according to the law of conservation of angular momentum, this is compensated by the fact that the Earth moves away from the Sun and according to the second Kepler's law its circulation period increases.

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For an observer located in the Northern Hemisphere, for example, in the European part of Russia, the Sun usually rises in the east and rises to the south, occupying the highest position in the sky at noon, then slopes to the west and disappears behind the horizon. This movement of the Sun is only visible and is caused by the rotation of the Earth around its axis. If you look at the Earth from above in the direction of the North Pole, it will rotate counterclockwise. At the same time, the Sun remains in place, the appearance of its movement is created due to the rotation of the Earth.

Annual rotation of the Earth

The Earth also rotates counterclockwise around the Sun: if you look at the planet from above, from the North Pole. Because the Earth's axis is tilted relative to its plane of rotation, it illuminates it unevenly as the Earth rotates around the Sun. Some areas receive more sunlight, others less. Thanks to this, the seasons change and the length of the day changes.

Spring and autumn equinox

Twice a year, on March 21 and September 23, the Sun illuminates the Northern and Southern Hemispheres equally. These moments are known as the autumn equinox. In March, autumn begins in the Northern Hemisphere, and autumn in the Southern Hemisphere. In September, on the contrary, autumn comes to the Northern Hemisphere, and spring to the Southern Hemisphere.

Summer and winter solstice

In the Northern Hemisphere, on June 22, the Sun rises highest above the horizon. The day has the longest duration, and the night on this day is the shortest. The winter solstice occurs on December 22 - the day has the shortest duration and the night has the longest. In the Southern Hemisphere, the opposite happens.

Polar night

Due to the tilt of the earth's axis, the polar and subpolar regions of the Northern Hemisphere are without sunlight during the winter months - the Sun does not rise above the horizon at all. This phenomenon is known as polar night. A similar polar night exists for the circumpolar regions of the Southern Hemisphere, the difference between them is exactly six months.

What gives the Earth its rotation around the Sun

Planets cannot help but revolve around their stars - otherwise they would simply be attracted and burnt up. The uniqueness of the Earth lies in the fact that its axis tilt of 23.44° turned out to be optimal for the emergence of all the diversity of life on the planet.

It is thanks to the tilt of the axis that the seasons change, there are different climatic zones that provide the diversity of the earth's flora and fauna. Changes in the heating of the earth's surface ensure the movement of air masses, which means precipitation in the form of rain and snow.

The distance from the Earth to the Sun of 149,600,000 km also turned out to be optimal. A little further, and water on Earth would only be in the form of ice. Any closer and the temperature would have been too high. The very emergence of life on Earth and the diversity of its forms became possible precisely thanks to the unique coincidence of so many factors.