In a year, the earth makes a complete revolution around. In which direction does the earth rotate? Renaissance and Modern times

Regardless of the fact that the constant movements of our planet are usually imperceptible, various scientific facts have long proved that the planet Earth moves along its own, strictly defined trajectory, not only around the Sun itself, but also around own axis. This is what determines the mass of natural phenomena observed by people every day, such as, for example, the change in the time of day and night. Even at this moment, reading these lines, you are in constant motion, motion, which is due to the movement of your native planet.

intermittent movement

Interestingly, the speed of the Earth itself is not a constant value, for reasons that scientists, unfortunately, have not yet been able to explain, however, it is known for certain that each of the centuries the Earth somewhat slows down the speed of its usual rotation by an amount equal to approximately 0, 0024 seconds. It is believed that such an anomaly is directly related to some kind of lunar attraction, which causes the ebb and flow, on which our planet also spends a significant proportion of its own energy, which “slows down” its individual rotation. The so-called tidal protrusions, usually moving in the opposite direction of the Earth, cause the emergence of certain frictional forces, which, in accordance with the laws of physics, are the main inhibitory factor in such a powerful space system as the Earth.

Of course, there is really no axis, it is an imaginary line that helps to make calculations.

In one hour, it is believed that the Earth makes a revolution of 15 degrees. For how much it turns around the axis completely, it is not difficult to guess: 360 degrees - in one day at 24 hours.

Day at 23 o'clock

It is clear that the Earth turns around its own axis in 24 hours familiar to people - an ordinary Earth day, or rather, in 23 hours minutes and almost 4 seconds. Movement occurs invariably from the western part to the eastern and nothing else. It is easy to calculate that under such conditions the speed at the equator will reach about 1670 kilometers per hour, gradually decreasing as it approaches the poles, where it smoothly passes to zero.

It is impossible to detect the rotation performed by the Earth at such a gigantic speed with the naked eye, because all the surrounding objects move along with people. All the planets in the solar system make similar movements. So, for example, Venus has a much lower speed of movement, which is why its day differs from the earth's by more than two hundred and forty-three times.

The fastest planets known today are Jupiter and the planet Saturn, making their full rotation around the axis in ten and ten and a half hours, respectively.

It should be noted that the rotation of the Earth around its axis is an extremely interesting and unknown fact that requires further close study by scientists around the world.

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 bowels, in the atmosphere and oceans, as well as in the near space.

The rotation of the Earth explains the change of day and night, the visible 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, bodies moving along its surface are affected by the Coriolis force, the influence of which is manifested in undermining of the right banks of rivers in the Northern Hemisphere and the left - in the Southern Hemisphere of the Earth and in some features of the atmospheric circulation. The centrifugal force generated by the rotation of the Earth partly explains the differences in the acceleration of gravity at the equator and the Earth's poles.

To study the patterns of the Earth's rotation, two coordinate systems are introduced with a common origin at the Earth's center of mass (Fig. 1.26). The terrestrial system X 1 Y 1 Z 1 participates in the daily rotation of the Earth and remains motionless relative to the points of the earth's surface. The XYZ star coordinate system is not related to the daily rotation of the Earth. Although its beginning moves in world space with some acceleration, participating in the annual movement of the Earth around the Sun in the Galaxy, but this movement 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 frame of reference. 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 the Earth's inertia as the axes of the Earth's coordinate system; another choice of axes is also possible. The position of the earth system relative to the star 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 is provided by observations of the daily motion of celestial bodies. The rotation of the Earth occurs from west to east, i.e. counterclockwise as viewed from the Earth's North Pole.

The average inclination of the equator to the ecliptic of the initial epoch (angle υ) is almost constant (in 1900 it was equal to 23° 27¢ 08.26² and increased by less than 0.1² during the 20th century). The line of intersection of the Earth's equator and the ecliptic of the initial epoch (the line of nodes) slowly moves along the ecliptic from east to west, moving 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. The angle between these axes, according to observations made since the end of the 19th century, does not exceed 0.4².

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

the point of the vernal equinox;

The center of the visible disk of the Sun, displaced by annual aberration ("true Sun");

· "Mean Sun" - a fictitious point, the position of which in the sky can be theoretically calculated for any moment of time.

Three different periods of time determined by these points are called sidereal, true solar and mean solar days, respectively.

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

where Pz is the duration of the earth day, T is the duration of a standard day (atomic), which is equal to 86400s;

- angular velocities corresponding to terrestrial and standard days.

Since the value of ω changes only in the ninth - eighth decimal place, then the values ​​of ν are of the order of 10 -9 -10 -8 .

The Earth makes one complete 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 as the Earth rotates.

The sidereal day is determined by the period of rotation of the Earth around its axis with respect 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 interval is taken as the length of the sidereal day the time between two successive upper climaxes 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 is constantly changing, which means that the location of the vernal equinox on the ecliptic changes accordingly. It has been established that a 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, hits the vernal equinox point earlier than it hits 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, the true solar day is longer than in summer. For example, at the end of December they are 24 hours 04 minutes 27 seconds, and in mid-September - 24 hours 03 minutes. 36sec. The average unit of a solar day is considered to be 24 hours 03 minutes. 56.5554 seconds sidereal time.

The angular velocity of the Earth relative to the Sun, due to the ellipticity of the Earth's orbit, depends on the time of year. The Earth orbits the slowest when it is at perihelion, the farthest point of its orbit 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 during the year. The right 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 a 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 joint 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, the mean solar day is used, tied to the so-called mean Sun - a conditional point moving evenly along the celestial equator, and not along the ecliptic, like the real Sun, and coinciding with the center of the Sun at the time of the vernal equinox. The period of revolution of the average Sun in the celestial sphere is equal to the tropical year.

Mean solar days are not subject to periodic changes, like true solar days, but their duration changes monotonously 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 about 0.0017 seconds per century. Thus, the duration of the mean 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 mean solar days. This value is a constant ratio of sidereal and solar time.

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

24h Wed solar time = 24h. 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. cf. 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 mean solar - is different on different meridians. But all points lying on the same meridian at the same 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 shortcoming to some extent, the Canadian S. Fleshing suggested introducing standard time, i.e. a time counting system based on the division of the Earth's surface into 24 time zones, each of which is 15 ° apart from the neighboring zone in longitude. Flushing plotted 24 major 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 conditionally plotted. The time of the same time zone at each moment for all its points was considered the same.

Before Flushing, maps with various prime meridians were published in many countries of 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 initial 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 meridian of the Greenwich Observatory as the initial or zero meridian, 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.

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

When counting time in calendar days, it is important to establish on which meridian a new date (day of the month) begins. By 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 decrease 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 clear that the new calendar month and New Year start on the international date line.

Thus, the prime meridian and the 180° E meridian, along which the international date line runs, 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 the time BC was the gnomon, in Greek a pointer, a vertical pillar on a leveled area, the shadow of which, changing its direction when the Sun moved, showed one or another 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 distributed 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. Gnomonics - the art of making sundials and the ability to use them - were dealt with by astronomers and mathematicians of the ancient world, the Middle Ages and modern times. In the 18th century and at the beginning of the 19th century. gnomonics was expounded in mathematics textbooks.

And only after 1955, when the requirements of physicists and astronomers to the accuracy of time increased greatly, it became impossible to be satisfied with the daily rotation of the Earth as a standard of time, 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 the angular momentum between different parts of the Earth (hydrosphere, mantle, liquid core). The meridian accepted for counting time 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 a change 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 reference (86,400 s). The shorter the Earth's day, the faster the Earth rotates.

Three components are distinguished in the magnitude of the change in the speed of the Earth's rotation: secular deceleration, periodic seasonal fluctuations, and irregular intermittent changes.

The secular deceleration of the Earth's rotation rate is due to the action of 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 perturbing body - the Moon or the Sun. In this case, the compression force of the Earth increases if the resultant coincides with the plane of the equator, 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 times the angular velocity) must remain constant, the rotation speed of the compressed Earth is less than that of the undeformed one. 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 with time. The compression of the Earth changes accordingly, which ultimately causes tidal fluctuations in the speed of the Earth's rotation. The most significant of these are fluctuations with semi-monthly and monthly periods.

The slowdown in the speed of the Earth's rotation is found in astronomical observations and paleontological studies. Observations of ancient solar eclipses led to the conclusion that the duration of a day increases by 2s every 100,000 years. Paleontological observations of corals have shown that warm sea corals grow to form a belt whose thickness 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 are found. According to paleontological observations (Table 5), the duration 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. 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 Earth's rotation was controlled by comparing the observed and calculated coordinates of the Moon, Sun, and planets. In this way, it was possible to get an idea of ​​the change in the speed of the Earth's rotation during the last three centuries - from the end of the 17th century, when the first instrumental observations of the motion of the Moon, Sun, and planets began to be made. An analysis of these data shows (Fig. 1.27) that from the beginning of the 17th century. until the middle of the 19th century. The speed of the Earth's rotation has changed little. From the second half of the 19th century Until now, significant irregular velocity fluctuations have been observed with characteristic times of the order of 60–70 years.

Fig.1.27. Deviation of the length of the day from the reference for 350 years

The Earth rotated most rapidly around 1870, when the duration of the Earth's day was 0.003 s shorter than the reference. The slowest - about 1903, when the Earth's day was longer than the reference day by 0.004 s. From 1903 to 1934 there was an acceleration of the rotation of the Earth, from the end of the 30s to 1972. there was a slowdown, and since 1973. The Earth is currently accelerating its rotation.

Periodic annual and semi-annual fluctuations in the rate of rotation of the Earth are explained by periodic changes in the moment of inertia of the Earth due to the seasonal dynamics of the atmosphere and the planetary distribution of precipitation. According to modern data, the length of the day during the year varies by ±0.001 seconds. At the same time, the shortest day falls on July-August, and the longest - on 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) - May 28, the maximum speed (acceleration is zero) - August 9, the average speed (minimum deceleration) - November 6.

Random changes in the speed of the Earth's rotation are also observed, which occur at irregular intervals, almost a multiple of eleven years. The absolute value of the relative change in the 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 speed of the Earth's rotation have been little studied. One of the hypotheses explains the irregular fluctuations in the angular velocity of the Earth's rotation by the recrystallization of certain rocks inside the Earth, which changes its moment of inertia.

Before the discovery of the unevenness of the Earth's rotation, the derived unit of time - the second - was defined as 1/86400 of the fraction of a mean solar day. The variability of the average solar day due to the uneven rotation of the Earth forced us to abandon such a definition of the second.

In October 1959 The International Bureau of Weights and Measures 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 so-defined second is called "ephemeris". The number 31556925.9747=86400´365.2421988 is the number of seconds in a tropical year whose duration for the year 1900, January 0, at 12 o'clock ephemeris time (uniform Newtonian time) was 365.2421988 mean solar days.

In other words, an ephemeris second is a time interval equal to 1/86400 of the average length of a mean solar day they had in 1900, January 0, at 12 o'clock 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 - a second of "atomic" time (SI second) - is equated 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 for several years. The standard of atomic time has neither diurnal nor secular fluctuations, does not age and has sufficient certainty, accuracy and reproducibility.

With the introduction of atomic time, the accuracy of determining the uneven rotation of the Earth has significantly improved. From that moment on, it became possible to register all fluctuations in the speed of the Earth's rotation 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 - accelerated again. This acceleration has not yet ended and will last until 2010. Acceleration of rotation 1958-1961 and slowdown 1989-1994. are short term fluctuations. Seasonal fluctuations lead to the fact that the speed of the Earth's rotation is the lowest in April and November, and the highest in January and July. The January maximum is much less than the July one. The difference between the minimum value of the 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 reference for 45 years

The study of the unevenness of the Earth's rotation, the nutations 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 the expansion of our knowledge in various fields of geosciences.

In the 80s of the 20th century, astronomical methods for determining the parameters of the Earth's rotation were replaced by new methods of geodesy. Doppler observations of satellites, laser ranging of the Moon and satellites, the global positioning system GPS, radio interferometry are effective tools 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 is the most efficient and independent of optical measurements tool for studying rotary motion Earth.

I remember a moment from my school years when my mother came up to me and turned my school globe 360 ​​degrees. Then she asked me: "Do you know, son, how many hours does it take for the earth to rotate on its axis?" I thought, and she continued: "But open the geography textbook and find out." I followed her advice and discovered something that I did not know before. So ...

How long does it take for one revolution of the Earth around itself?

Our planet makes a complete revolution around its axis in exactly 24 hours. And so the days go by. They are called "sunny" for days.

The planet itself rotates from west to east. And when viewed from the north pole of the ecliptic (or from the North Star), rotation occurs counterclock-wise.

It is thanks to this whirl that change of days and nights. After all, one half is illuminated by the sun's rays, and the other remains in the shade.

In addition, the rotation of the planet is facilitated by deviations of moving streams (for example, rivers or winds) in the northern hemisphere - to the right side, and in the southern - to the left.

History of ideas about the daily rotation of the Earth

At different times, people in their own way tried to explain the change of day. Hypotheses often replaced each other, each people of antiquity had its own theory:

• the earliest explanation of the daily change of the firmament was given by during the time of Pythagoras. It was believed that the Earth in the system of the world of Philolaus made certain movements. But they were not rotational, but progressive. And these movements passed through the so-called "Central Fire";
• the first of the ancient astronomers who claimed that our planet was precisely revolves, became an Indian scientist Aryabhata(who lived at the end of the fifth century - the beginning of the sixth);
• then, in the second half of the 19th century, in Europe there were more detailed discussions about the possibilities of the Earth's movements. The most widely written about this were such Parisian scientists as Jean Buridan, Nicholas Orem and Albert of Saxony;
• famous in 1543 Nicholas Copernicus already wrote my job"On the rotation of the heavenly spheres" , which was supported by many astronomers of that time;
• and later Galileo Galileiformulated a fundamental principle of relativity. He claimed that the movement of the Earth (or any other object) does not affect the ongoing internal and external processes.

These were the main stages in the development of the hypothesis about the rotation of our planet. It was the understanding of the problems associated with this topic that contributed to the discovery of many laws of mechanics and origin new cosmology.

The period of revolution of the Earth around its axis is a constant value. Astronomically, it is equal to 23 hours 56 minutes and 4 seconds. However, scientists did not take into account the insignificant error, rounding these figures up to 24 hours, or one Earth day. One such revolution is called a daily rotation and occurs from west to east. For a person from Earth, it looks like morning, afternoon and evening, replacing each other. In other words, the sunrise, noon and sunset of the sun completely coincide with the daily rotation of the planet.

What is the Earth's axis?

The Earth's axis can be mentally represented as an imaginary line around which the third planet from the Sun rotates. This axis crosses the surface of the Earth at two constant points - at the North and South geographic poles. If, for example, we mentally continue the direction of the earth's axis upwards, then it will pass next to the North Star. By the way, this explains the immobility of the North Star. The effect is created that the celestial sphere moves around the axis, and therefore around this star.

It also seems to a person from Earth that the starry sky rotates in the direction from east to west. But it's not. The apparent movement is only a reflection of the true diurnal rotation. It is important to know that our planet simultaneously participates in not one, but at least two processes. It revolves around the earth's axis and makes an orbital motion around the celestial body.

The apparent movement of the Sun is also a reflection of the true movement of our planet in its orbit around it. As a result, first comes the day, and then - the night. Note that one movement is unthinkable without the other! These are the laws of the universe. Moreover, if the period of revolution of the Earth around its axis is equal to one Earth day, then the time of its movement around the celestial body is a variable value. Let's find out what influences these indicators.

What affects the speed of the Earth's orbital rotation?

The period of revolution of the Earth around its axis is a constant value, which cannot be said about the speed with which the blue planet moves in orbit around the star. For a long time, astronomers thought that this speed was constant. It turned out not! Currently, thanks to the most accurate measuring instruments, scientists have found a slight deviation in the previously obtained figures.

The reason for this variability is the friction that occurs during sea tides. It is it that directly affects the decrease in the orbital speed of the third planet from the Sun. In turn, the ebbs and flows are a consequence of the action on the Earth of its permanent satellite - the Moon. A person does not notice such a revolution of the planet around the heavenly body, as well as the period of rotation of the Earth around its axis. But we cannot help but pay attention to spring giving way to summer, summer to autumn, and autumn to winter. And this happens all the time. This is the consequence of the orbital movement of the planet, which lasts 365.25 days, or one Earth year.

It is worth noting that the Earth moves relative to the Sun unevenly. For example, at some points it is closest to the heavenly body, and at others it is the most distant from it. And one more thing: the orbit around the Earth is not a circle, but an oval, or an ellipse.

Why does a person not notice the daily rotation?

A person will never be able to notice the rotation of the planet, being on its surface. This is due to the difference in the size of ours and the globe - it is too huge for us! The period of revolution of the Earth around its axis cannot be noticed in any way, but it will be possible to feel: the day will be replaced by night and vice versa. This has already been discussed above. But what would happen if the blue planet could not rotate around its axis? And here's what: on one side of the Earth there would be eternal day, and on the other - eternal night! Terrible, isn't it?

It is important to know!

So, the period of the Earth's revolution around its axis is almost 24 hours, and the time of its "journey" around the Sun is about 365.25 days (one Earth year), since this value is not constant. Let us draw your attention to the fact that, in addition to the two considered movements, the Earth also participates in others. For example, she, along with the rest of the planets, moves relative to the Milky Way - our native Galaxy. In turn, it makes some movement relative to other neighboring galaxies. And everything happens because there has never been and never will be anything immutable and immovable in the Universe! This must be remembered for the rest of your life.

Our planet is in constant motion, it revolves around the Sun and its own axis. The earth's axis is an imaginary line drawn from the North to the South Pole (they remain motionless during rotation) at an angle of 66 0 33 ꞌ with respect to the plane of the Earth. People cannot notice the moment of rotation, because all objects are moving in parallel, their speed is the same. It would look exactly the same as if we were sailing on a ship and did not notice the movement of objects and objects on it.

A full rotation around the axis is completed within one sidereal day, consisting of 23 hours 56 minutes and 4 seconds. During this interval, then one or the other side of the planet turns towards the Sun, receiving from it a different amount of heat and light. In addition, the rotation of the Earth around its axis affects its shape (flattened poles are the result of the planet's rotation around the axis) and the deviation when bodies move in a horizontal plane (rivers, currents and winds of the Southern Hemisphere deviate to the left, Northern - to the right).

Linear and angular speed of rotation

(Earth rotation)

The linear speed of the Earth's rotation around its axis is 465 m/s or 1674 km/h in the equatorial zone, as we move away from it, the speed gradually slows down, at the North and South Poles it is equal to zero. For example, for citizens of the equatorial city of Quito (the capital of Ecuador in South America) the rotation speed is just 465 m/s, and for Muscovites living on the 55th parallel north of the equator - 260 m/s (almost half as much).

Every year, the speed of rotation around the axis decreases by 4 milliseconds, which is associated with the influence of the Moon on the strength of sea and ocean ebb and flow. The pull of the Moon "pulls" the water in the opposite direction to the Earth's axial rotation, creating a slight frictional force that slows the rotation rate by 4 milliseconds. The rate of angular rotation remains the same everywhere, its value is 15 degrees per hour.

Why does day turn into night

(The change of night and day)

The time of a complete rotation of the Earth around its axis is one sidereal day (23 hours 56 minutes 4 seconds), during this time period the side illuminated by the Sun is first “in the power” of the day, the shadow side is at the mercy of the night, and then vice versa.

If the Earth rotated differently and one side of it was constantly turned towards the Sun, then there would be a high temperature (up to 100 degrees Celsius) and all the water would evaporate, on the other side, frost would rage and the water would be under a thick layer of ice. Both the first and second conditions would be unacceptable for the development of life and the existence of the human species.

Why do the seasons change

(Change of seasons on earth)

Due to the fact that the axis is inclined with respect to the earth's surface at a certain angle, its sections are obtained in different time different amounts of heat and light, which causes the change of seasons. According to the astronomical parameters necessary to determine the time of year, some points in time are taken as reference points: for summer and winter, these are the days of the solstice (June 21 and December 22), for spring and autumn - the Equinoxes (March 20 and September 23). From September to March, the Northern Hemisphere is turned towards the Sun for less time and, accordingly, receives less heat and light, hello winter-winter, the Southern Hemisphere at this time receives a lot of heat and light, long live summer! 6 months pass and the Earth moves to the opposite point of its orbit and the Northern Hemisphere already receives more heat and light, the days become longer, the Sun rises higher - summer is coming.

If the Earth were located in relation to the Sun exclusively in a vertical position, then the seasons would not exist at all, because all points on the half illuminated by the Sun would receive the same and uniform amount of heat and light.