How the earth and sun rotate. At what speed does the earth rotate around its axis?

V = (R e R p R p 2 + R e 2 t g 2 φ + R p 2 h R p 4 + R e 4 t g 2 φ) ω (\displaystyle v=\left((\frac (R_(e) \,R_(p))(\sqrt ((R_(p))^(2)+(R_(e))^(2)\,(\mathrm (tg) ^(2)\varphi )))) +(\frac ((R_(p))^(2)h)(\sqrt ((R_(p))^(4)+(R_(e))^(4)\,\mathrm (tg) ^ (2)\varphi )))\right)\omega ), Where R e (\displaystyle R_(e))= 6378.1 km - equatorial radius, R p (\displaystyle R_(p))= 6356.8 km - polar radius.

• An airplane flying at this speed from east to west (at an altitude of 12 km: 936 km/h at the latitude of Moscow, 837 km/h at the latitude of St. Petersburg) will be at rest in the inertial reference frame.
• The superposition of the rotation of the Earth around its axis with a period of one sidereal day and around the Sun with a period of one year leads to the inequality of solar and sidereal days: the length of the average solar day is exactly 24 hours, which is 3 minutes 56 seconds longer than the sidereal day.

Physical meaning and experimental confirmation

The physical meaning of the Earth's rotation around its axis

Since any movement is relative, it is necessary to indicate a specific reference system relative to which the movement of a particular body is studied. When they say that the Earth rotates around an imaginary axis, it is meant that it performs rotational motion relative to any inertial reference frame, and the period of this rotation is equal to a sidereal day - the period of a complete revolution of the Earth (celestial sphere) relative to the celestial sphere (Earth).

All experimental evidence of the rotation of the Earth around its axis comes down to the proof that the reference system associated with the Earth is a non-inertial reference system of a special type - a reference system that performs rotational motion relative to inertial reference systems.

Unlike inertial motion (that is, uniform rectilinear motion relative to inertial frames of reference), to detect non-inertial motion of a closed laboratory it is not necessary to make observations of external bodies - such motion is detected using local experiments (that is, experiments carried out inside this laboratory). In this sense of the word, non-inertial motion, including the rotation of the Earth around its axis, can be called absolute.

Inertia forces

Effects of centrifugal force

Dependence of free fall acceleration on geographic latitude. Experiments show that the acceleration of free fall depends on geographic latitude: the closer to the pole, the greater it is. This is explained by the action of centrifugal force. Firstly, points on the earth's surface located at higher latitudes are closer to the axis of rotation and, therefore, when approaching the pole, the distance r (\displaystyle r) decreases from the axis of rotation, reaching zero at the pole. Secondly, with increasing latitude, the angle between the centrifugal force vector and the horizon plane decreases, which leads to a decrease in the vertical component of the centrifugal force.

This phenomenon was discovered in 1672, when the French astronomer Jean Richet, while on an expedition in Africa, discovered that the pendulum clock at the equator runs slower than in Paris. Newton soon explained this by saying that the period of oscillation of a pendulum is inversely proportional to the square root of the acceleration due to gravity, which decreases at the equator due to the action of centrifugal force.

Oblateness of the Earth. The influence of centrifugal force leads to the oblateness of the Earth at the poles. This phenomenon, predicted by Huygens and Newton at the end of the 17th century, was first discovered by Pierre de Maupertuis in the late 1730s as a result of processing data from two French expeditions specially equipped to solve this problem in Peru (led by Pierre Bouguer and Charles de la Condamine ) and Lapland (under the leadership of Alexis Clairaut and Maupertuis himself).

Coriolis force effects: laboratory experiments

This effect should be most clearly expressed at the poles, where the period of complete rotation of the pendulum plane is equal to the period of rotation of the Earth around its axis (sidereal day). In general, the period is inversely proportional to the sine of geographic latitude; at the equator, the plane of oscillation of the pendulum is unchanged.

Gyroscope- a rotating body with a significant moment of inertia retains its angular momentum if there are no strong disturbances. Foucault, who was tired of explaining what happens to a Foucault pendulum not at the pole, developed another demonstration: a suspended gyroscope maintained its orientation, which means it turned slowly relative to the observer.

Deflection of projectiles during gun firing. Another observable manifestation of the Coriolis force is the deflection of the trajectories of projectiles (to the right in the northern hemisphere, to the left in the southern hemisphere) fired in a horizontal direction. From the point of view of the inertial reference system, for projectiles fired along the meridian, this is due to the dependence of the linear speed of rotation of the Earth on geographic latitude: when moving from the equator to the pole, the projectile retains the horizontal component of the speed unchanged, while the linear speed of rotation of points on the earth's surface decreases , which leads to a displacement of the projectile from the meridian in the direction of the Earth’s rotation. If the shot was fired parallel to the equator, then the displacement of the projectile from parallel is due to the fact that the trajectory of the projectile lies in the same plane with the center of the Earth, while points on the earth's surface move in a plane perpendicular to the Earth's rotation axis. This effect (for the case of shooting along the meridian) was predicted by Grimaldi in the 40s of the 17th century. and first published by Riccioli in 1651.

Deviation of freely falling bodies from the vertical. ( ) If the speed of a body has a large vertical component, the Coriolis force is directed to the east, which leads to a corresponding deviation of the trajectory of a body freely falling (without initial speed) from a high tower. When considered in an inertial reference frame, the effect is explained by the fact that the top of the tower relative to the center of the Earth moves faster than the base, due to which the trajectory of the body turns out to be a narrow parabola and the body is slightly ahead of the base of the tower.

The Eötvös effect. At low latitudes, the Coriolis force, when moving along the earth's surface, is directed in the vertical direction and its action leads to an increase or decrease in the acceleration of gravity, depending on whether the body is moving west or east. This effect is called the Eötvös effect in honor of the Hungarian physicist Loránd Eötvös, who experimentally discovered it at the beginning of the 20th century.

Experiments using the law of conservation of angular momentum. Some experiments are based on the law of conservation of angular momentum: in an inertial reference frame, the magnitude of angular momentum (equal to the product of the moment of inertia and the angular velocity of rotation) does not change under the influence of internal forces. If at some initial moment of time the installation is stationary relative to the Earth, then the speed of its rotation relative to the inertial reference system is equal to the angular speed of rotation of the Earth. If you change the moment of inertia of the system, then the angular speed of its rotation should change, that is, rotation relative to the Earth will begin. In a non-inertial reference frame associated with the Earth, rotation occurs as a result of the Coriolis force. This idea was proposed by the French scientist Louis Poinsot in 1851.

The first such experiment was carried out by Hagen in 1910: two weights on a smooth crossbar were installed motionless relative to the surface of the Earth. Then the distance between the loads was reduced. As a result, the installation began to rotate. An even more demonstrative experiment was carried out by the German scientist Hans Bucka in 1949. A rod approximately 1.5 meters long was installed perpendicular to a rectangular frame. Initially, the rod was horizontal, the installation was motionless relative to the Earth. Then the rod was brought into a vertical position, which led to a change in the moment of inertia of the installation by approximately 10 4 times and its rapid rotation with an angular velocity 10 4 times higher than the speed of rotation of the Earth.

Funnel in the bath.

Since the Coriolis force is very weak, it has a negligible effect on the direction of swirl of water when draining a sink or bathtub, so in general the direction of rotation in the funnel is not related to the rotation of the Earth. Only in carefully controlled experiments can the effect of the Coriolis force be separated from other factors: in the northern hemisphere the funnel will spin counterclockwise, in the southern hemisphere - vice versa.

Coriolis force effects: phenomena in the surrounding nature

Optical experiments

A number of experiments demonstrating the rotation of the Earth are based on the Sagnac effect: if a ring interferometer performs a rotational motion, then due to relativistic effects a phase difference appears in the counterpropagating beams

Where A (\displaystyle A)- area of ​​projection of the ring onto the equatorial plane (the plane perpendicular to the axis of rotation), c (\displaystyle c)- speed of light, ω (\displaystyle \omega )- angular speed of rotation. To demonstrate the rotation of the Earth, this effect was used by the American physicist Michelson in a series of experiments carried out in 1923-1925. In modern experiments using the Sagnac effect, the rotation of the Earth must be taken into account to calibrate ring interferometers.

There are a number of other experimental demonstrations of the Earth's diurnal rotation.

Uneven rotation

Precession and nutation

History of the idea of ​​the Earth's daily rotation

Antiquity

The explanation of the daily rotation of the sky by the rotation of the Earth around its axis was first proposed by representatives of the Pythagorean school, the Syracusans Hicetus and Ecphantus. According to some reconstructions, the rotation of the Earth was also confirmed by the Pythagorean Philolaus from Croton (5th century BC). A statement that can be interpreted as an indication of the rotation of the Earth is contained in Plato's dialogue Timaeus .

However, virtually nothing is known about Hicetas and Ecphantes, and even their very existence is sometimes questioned. According to the opinion of most scientists, the Earth in Philolaus’ world system did not perform a rotational, but a translational movement around the Central Fire. In his other works, Plato follows the traditional view that the Earth is immobile. However, numerous evidence has reached us that the idea of ​​the rotation of the Earth was defended by the philosopher Heraclides of Pontus (IV century BC). Probably, another assumption of Heraclides is associated with the hypothesis of the rotation of the Earth around its axis: each star represents a world, including earth, air, ether, and all this is located in infinite space. Indeed, if the daily rotation of the sky is a reflection of the rotation of the Earth, then the prerequisite for considering the stars to be on the same sphere disappears.

About a century later, the assumption of the rotation of the Earth became part of the first, proposed by the great astronomer Aristarchus of Samos (3rd century BC). Aristarchus was supported by the Babylonian Seleucus (2nd century BC), as well as Heraclides of Pontus, who considered the Universe to be infinite. The fact that the idea of ​​the daily rotation of the Earth had its supporters back in the 1st century AD. e., evidenced by some statements of the philosophers Seneca, Dercyllidas, and the astronomer Claudius Ptolemy. The vast majority of astronomers and philosophers, however, did not doubt the immobility of the Earth.

Arguments against the idea of ​​the Earth's motion are found in the works of Aristotle and Ptolemy. So, in his treatise About Heaven Aristotle justifies the immobility of the Earth by the fact that on a rotating Earth, bodies thrown vertically upward could not fall to the point from which their movement began: the surface of the Earth would shift under the thrown body. Another argument in favor of the immobility of the Earth, given by Aristotle, is based on his physical theory: the Earth is a heavy body, and heavy bodies tend to move towards the center of the world, and not rotate around it.

From the work of Ptolemy it follows that supporters of the hypothesis of the rotation of the Earth responded to these arguments that both air and all earthly objects move together with the Earth. Apparently, the role of air in this argument is fundamentally important, since it is implied that it is its movement together with the Earth that hides the rotation of our planet. Ptolemy objects to this:

bodies in the air will always seem to lag behind... And if the bodies rotated with the air as one whole, then none of them would seem to be ahead of or behind the other, but would remain in place, in flight and throwing it would not make deviations or movements to another place, like those that we personally see taking place, and they would not slow down or accelerate at all, because the Earth is not motionless.

Middle Ages

India

The first medieval author to suggest that the Earth rotates around its axis was the great Indian astronomer and mathematician Aryabhata (late 5th - early 6th centuries). He formulates it in several places in his treatise Aryabhatiya, For example:

Just as a man on a forward-moving ship sees fixed objects moving backward, so an observer... sees the fixed stars moving in a straight line to the west.

It is not known whether this idea belongs to Aryabhata himself or whether he borrowed it from ancient Greek astronomers.

Aryabhata was supported by only one astronomer, Prthudaka (9th century). Most Indian scientists defended the immobility of the Earth. Thus, the astronomer Varahamihira (6th century) argued that on a rotating Earth, birds flying in the air could not return to their nests, and stones and trees would fly off the surface of the Earth. The outstanding astronomer Brahmagupta (6th century) also repeated the old argument that a body that fell from a high mountain could sink to its base. At the same time, he, however, rejected one of Varahamihira’s arguments: in his opinion, even if the Earth rotated, objects could not come off it due to their gravity.

Islamic East

The possibility of rotation of the Earth was considered by many scientists of the Muslim East. Thus, the famous geometer al-Sijizi invented the astrolabe, the operating principle of which is based on this assumption. Some Islamic scholars (whose names have not reached us) even found the correct way to refute the main argument against the rotation of the Earth: the verticality of the trajectories of falling bodies. Essentially, the principle of superposition of movements was put forward, according to which any movement can be decomposed into two or more components: in relation to the surface of the rotating Earth, a falling body moves along a plumb line, but a point that is a projection of this line onto the surface of the Earth would be transferred by it rotation. This is evidenced by the famous encyclopedist al-Biruni, who himself, however, was inclined to the immobility of the Earth. In his opinion, if some additional force acts on the falling body, then the result of its action on the rotating Earth will lead to some effects that are not actually observed.

Among scientists of the 13th-16th centuries associated with the Maragha and Samarkand observatories, a discussion arose about the possibility of an empirical substantiation of the immobility of the Earth. Thus, the famous astronomer Qutb ad-Din ash-Shirazi (XIII-XIV centuries) believed that the immobility of the Earth could be verified by experiment. On the other hand, the founder of the Maragha Observatory, Nasir ad-Din al-Tusi, believed that if the Earth rotated, then this rotation would be divided by a layer of air adjacent to its surface, and all movements near the surface of the Earth would occur exactly the same as if the Earth was motionless. He substantiated this with the help of observations of comets: according to Aristotle, comets are a meteorological phenomenon in the upper layers of the atmosphere; however, astronomical observations show that comets take part in the daily rotation of the celestial sphere. Consequently, the upper layers of air are carried away by the rotation of the sky, therefore the lower layers can also be carried away by the rotation of the Earth. Thus, the experiment cannot answer the question of whether the Earth rotates. However, he remained a supporter of the immobility of the Earth, since this was in accordance with the philosophy of Aristotle.

Most Islamic scholars of later times (al-Urdi, al-Qazwini, an-Naysaburi, al-Jurjani, al-Birjandi and others) agreed with al-Tusi that all physical phenomena on a rotating and stationary Earth would occur in the same way. However, the role of air was no longer considered fundamental: not only air, but also all objects are transported by the rotating Earth. Consequently, to justify the immobility of the Earth it is necessary to involve the teachings of Aristotle.

A special position in these disputes was taken by the third director of the Samarkand Observatory, Alauddin Ali al-Kushchi (XV century), who rejected the philosophy of Aristotle and considered the rotation of the Earth physically possible. In the 17th century, the Iranian theologian and encyclopedist Baha ad-Din al-Amili came to a similar conclusion. In his opinion, astronomers and philosophers have not provided sufficient evidence to refute the rotation of the Earth.

Latin West

A detailed discussion of the possibility of the Earth's movement is widely contained in the writings of the Parisian scholastics Jean-Buridan, Albert of Saxony, and Nicholas of Oresme (second half of the 14th century). The most important argument in favor of the rotation of the Earth rather than the sky, given in their works, is the smallness of the Earth compared to the Universe, which makes attributing the daily rotation of the sky to the Universe highly unnatural.

However, all of these scientists ultimately rejected the rotation of the Earth, although on different grounds. Thus, Albert of Saxony believed that this hypothesis was not capable of explaining the observed astronomical phenomena. Buridan and Oresme rightly disagreed with this, according to whom celestial phenomena should occur in the same way regardless of whether the rotation is made by the Earth or the Cosmos. Buridan was able to find only one significant argument against the rotation of the Earth: arrows fired vertically upward fall down a vertical line, although with the rotation of the Earth they, in his opinion, should lag behind the movement of the Earth and fall west of the point of the shot.

But even this argument was rejected by Oresme. If the Earth rotates, then the arrow flies vertically upward and at the same time moves east, being captured by the air rotating with the Earth. Thus, the arrow should fall in the same place from where it was fired. Although the enthralling role of air is again mentioned here, it does not really play a special role. The following analogy speaks to this:

Likewise, if the air were closed in a moving ship, then to a person surrounded by this air it would seem that the air was not moving... If a person were in a ship moving at high speed to the east, unaware of this movement, and if he extended his hand in a straight line along the mast of the ship, it would seem to him that his hand was making a linear movement; in the same way, according to this theory, it seems to us that the same thing happens to an arrow when we shoot it vertically up or vertically down. Inside a ship moving at high speed to the east, all kinds of motion can take place: longitudinal, transverse, down, up, in all directions - and they appear exactly the same as when the ship is stationary.

Next, Oresme gives a formulation that anticipates the principle of relativity:

I conclude, therefore, that it is impossible to demonstrate by any experiment that the heavens have a diurnal movement and that the earth does not.

However, Oresme's final verdict on the possibility of the Earth's rotation was negative. The basis for this conclusion was the text of the Bible:

However, so far everyone supports and I believe that it is [Heaven] and not the Earth that moves, for “God made the circle of the Earth, which will not be moved,” despite all the arguments to the contrary.

The possibility of the daily rotation of the Earth was also mentioned by medieval European scientists and philosophers of later times, but no new arguments were added that were not contained in Buridan and Oresme.

Thus, almost none of the medieval scientists accepted the hypothesis of the rotation of the Earth. However, during its discussion, scientists of the East and West expressed many deep thoughts, which would later be repeated by scientists of the New Age.

Renaissance and Modern Times

In the first half of the 16th century, several works were published that argued that the cause of the daily rotation of the sky was the rotation of the Earth around its axis. One of them was the treatise of the Italian Celio Calcagnini “On the fact that the sky is motionless and the Earth rotates, or on the perpetual motion of the Earth” (written around 1525, published in 1544). He did not make much of an impression on his contemporaries, since by that time the fundamental work of the Polish astronomer Nicolaus Copernicus “On the Rotations of the Celestial Spheres” (1543) had already been published, where the hypothesis of the daily rotation of the Earth became part of the heliocentric system of the world, like Aristarchus of Samos. . Copernicus previously outlined his thoughts in a small handwritten essay Small Comment(not earlier than 1515). Two years earlier than the main work of Copernicus, the work of the German astronomer Georg Joachim Rheticus was published First narration(1541), where Copernicus' theory was popularly expounded.

In the 16th century, Copernicus was fully supported by astronomers Thomas Digges, Rheticus, Christoph Rothmann, Michael Möstlin, physicists Giambatista Benedetti, Simon Stevin, philosopher Giordano Bruno, and theologian Diego de Zuniga. Some scientists accepted the rotation of the Earth around its axis, rejecting its translational motion. This was the position of the German astronomer Nicholas Reimers, also known as Ursus, as well as the Italian philosophers Andrea Cesalpino and Francesco Patrizi. The point of view of the outstanding physicist William Hilbert, who supported the axial rotation of the Earth, but did not speak out about its translational motion, is not entirely clear. At the beginning of the 17th century, the heliocentric system of the world (including the rotation of the Earth around its axis) received impressive support from Galileo Galilei and Johannes Kepler. The most influential opponents of the idea of ​​the Earth's movement in the 16th and early 17th centuries were the astronomers Tycho Brahe and Christopher Clavius.

The hypothesis about the rotation of the Earth and the formation of classical mechanics

Essentially, in the XVI-XVII centuries. the only argument in favor of the axial rotation of the Earth was that in this case there is no need to attribute enormous rotation rates to the stellar sphere, because even in antiquity it was already reliably established that the size of the Universe significantly exceeds the size of the Earth (this argument was also contained in Buridan and Oresme) .

Considerations based on the dynamic concepts of that time were expressed against this hypothesis. First of all, this is the verticality of the trajectories of falling bodies. Other arguments also appeared, for example, equal firing range in the eastern and western directions. Answering the question about the unobservability of the effects of daily rotation in earthly experiments, Copernicus wrote:

Not only the Earth rotates with the water element connected to it, but also a considerable part of the air and everything that is in any way akin to the Earth, or the air closest to the Earth, saturated with earthly and watery matter, follows the same laws of nature as The Earth, or has acquired motion, which is imparted to it by the adjacent Earth in constant rotation and without any resistance

Thus, the main role in the unobservability of the Earth’s rotation is played by the entrainment of air by its rotation. The majority of Copernicans in the 16th century shared the same opinion.

Proponents of the infinity of the Universe in the 16th century were also Thomas Digges, Giordano Bruno, Francesco Patrizi - they all supported the hypothesis that the Earth rotates around its axis (and the first two also around the Sun). Christoph Rothmann and Galileo Galilei believed that stars were located at different distances from the Earth, although they did not explicitly speak about the infinity of the Universe. On the other hand, Johannes Kepler denied the infinity of the Universe, although he was a supporter of the rotation of the Earth.

Religious context of the Earth's rotation debate

A number of objections to the rotation of the Earth were associated with its contradictions with the text of Holy Scripture. These objections were of two types. Firstly, some places in the Bible were cited to confirm that it is the Sun that makes the daily movement, for example:

The sun rises and the sun sets, and hastens to its place where it rises.

In this case, the axial rotation of the Earth was affected, since the movement of the Sun from east to west is part of the daily rotation of the sky. A passage from the book of Joshua was often quoted in this connection:

Jesus cried to the Lord on the day that the Lord delivered the Amorites into the hands of Israel, when he defeated them in Gibeon, and they were beaten before the children of Israel, and said before the Israelites: Stand, O sun, over Gibeon, and the moon, over the valley of Avalon. !

Since the command to stop was given to the Sun, and not to the Earth, it was concluded that it was the Sun that performed the daily movement. Other passages have been cited in support of the Earth's immobility, for example:

You have set the earth on firm foundations: it will not be shaken for ever and ever.

These passages were considered to contradict both the view that the Earth rotates on its axis and the revolution around the Sun.

Proponents of the rotation of the Earth (notably Giordano-Bruno, Johannes-Kepler, and especially Galileo-Galilei) advocated on several fronts. First, they pointed out that the Bible was written in a language understandable to ordinary people, and if its authors provided scientifically clear language, it would not be able to fulfill its main, religious mission. Thus, Bruno wrote:

In many cases it is foolish and inadvisable to make much reasoning according to truth rather than according to the given case and convenience. For example, if instead of the words: “The sun is born and rises, passes through noon and inclines towards Aquilon,” the sage said: “The earth goes in a circle to the east and, leaving the sun, which sets, inclines towards the two tropics, from Cancer to the South, from Capricorn to Aquilon,” then the listeners would begin to think: “How? Does he say the earth moves? What kind of news is this? In the end they would consider him a fool, and he would indeed be a fool.

This kind of answer was given mainly to objections concerning the diurnal movement of the Sun. Secondly, it was noted that some passages of the Bible should be interpreted allegorically (see the article Biblical allegorism). Thus, Galileo noted that if Holy Scripture is taken literally in its entirety, it will turn out that God has hands, is subject to emotions such as anger, etc. In general, the main idea of ​​the defenders of the doctrine of the movement of the Earth was that science and religion have different goals: science examines the phenomena of the material world, guided by the arguments of reason, the goal of religion is the moral improvement of man, his salvation. Galileo in this regard quoted Cardinal Baronio that the Bible teaches how to ascend to heaven, not how heaven works.

These arguments were considered unconvincing by the Catholic Church, and in 1616 the doctrine of the rotation of the Earth was prohibited, and in 1631 Galileo was convicted by the Inquisition for his defense. However, outside Italy, this ban did not have a significant impact on the development of science and contributed mainly to the decline in the authority of the Catholic Church itself.

It must be added that religious arguments against the movement of the Earth were given not only by church leaders, but also by scientists (for example, Tycho Brahe). On the other hand, the Catholic monk Paolo Foscarini wrote a short essay “Letter on the views of the Pythagoreans and Copernicus on the mobility of the Earth and the immobility of the Sun and on the new Pythagorean system of the universe” (1615), where he expressed considerations close to those of Galileo, and the Spanish theologian Diego de Zuniga even used Copernican theory to interpret some passages of Scripture (although he later changed his mind). Thus, the conflict between theology and the doctrine of the movement of the Earth was not so much a conflict between science and religion as such, but a conflict between old (already outdated by the beginning of the 17th century) and new methodological principles underlying science.

The significance of the hypothesis about the rotation of the Earth for the development of science

Understanding the scientific problems raised by the theory of the rotating Earth contributed to the discovery of the laws of classical mechanics and the creation of a new cosmology, which is based on the idea of ​​​​the boundlessness of the Universe. Discussed during this process, the contradictions between this theory and the literalist reading of the Bible contributed to the demarcation of natural science and religion.

Our planet is constantly in motion:

• rotation around its own axis, movement around the Sun;
• rotation with the Sun around the center of our galaxy;
• movement relative to the center of the Local Group of galaxies and others.

Movement of the Earth around its own axis

Rotation of the Earth around its axis(Fig. 1). The earth's axis is taken to be an imaginary line around which it rotates. This axis is deviated by 23°27" from the perpendicular to the ecliptic plane. The Earth's axis intersects with the Earth's surface at two points - the poles - North and South. When viewed from the North Pole, the Earth's rotation occurs counterclockwise, or, as is commonly believed, with west to east. The planet completes a full rotation around its axis in one day.

Rice. 1. Rotation of the Earth around its axis

A day is a unit of time. There are sidereal and solar days.

Sidereal day- this is the period of time during which the Earth will turn around its axis in relation to the stars. They are equal to 23 hours 56 minutes 4 seconds.

Sunny day- this is the period of time during which the Earth turns around its axis in relation to the Sun.

The angle of rotation of our planet around its axis is the same at all latitudes. In one hour, each point on the Earth's surface moves 15° from its original position. But at the same time, the speed of movement is inversely proportional to the geographic latitude: at the equator it is 464 m/s, and at a latitude of 65° it is only 195 m/s.

The rotation of the Earth around its axis in 1851 was proved in his experiment by J. Foucault. In Paris, in the Pantheon, a pendulum was hung under the dome, and under it a circle with divisions. With each subsequent movement, the pendulum ended up on new divisions. This can only happen if the surface of the Earth under the pendulum rotates. The position of the pendulum's swing plane at the equator does not change, because the plane coincides with the meridian. The Earth's axial rotation has important geographical consequences.

When the Earth rotates, centrifugal force arises, which plays an important role in shaping the shape of the planet and reduces the force of gravity.

Another of the most important consequences of axial rotation is the formation of a rotational force - Coriolis forces. In the 19th century it was first calculated by a French scientist in the field of mechanics G. Coriolis (1792-1843). This is one of the inertia forces introduced to take into account the influence of rotation of a moving frame of reference on the relative motion of a material point. Its effect can be briefly expressed as follows: every moving body in the Northern Hemisphere is deflected to the right, and in the Southern Hemisphere - to the left. At the equator, the Coriolis force is zero (Fig. 3).

Rice. 3. Action of the Coriolis force

The action of the Coriolis force extends to many phenomena of the geographical envelope. Its deflecting effect is especially noticeable in the direction of movement of air masses. Under the influence of the deflecting force of the Earth's rotation, the winds of temperate latitudes of both hemispheres take a predominantly western direction, and in tropical latitudes - eastern. A similar manifestation of the Coriolis force is found in the direction of movement of ocean waters. The asymmetry of river valleys is also associated with this force (the right bank is usually high in the Northern Hemisphere, and the left bank in the Southern Hemisphere).

The rotation of the Earth around its axis also leads to the movement of solar illumination across the earth's surface from east to west, i.e., to the change of day and night.

The change of day and night creates a daily rhythm in living and inanimate nature. The circadian rhythm is closely related to light and temperature conditions. The daily variation of temperature, day and night breezes, etc. are well known. Circadian rhythms also occur in living nature - photosynthesis is possible only during the day, most plants open their flowers at different hours; Some animals are active during the day, others at night. Human life also flows in a circadian rhythm.

Another consequence of the Earth’s rotation around its axis is the time difference at different points on our planet.

Since 1884, zone time was adopted, that is, the entire surface of the Earth was divided into 24 time zones of 15° each. Behind standard time take the local time of the middle meridian of each zone. Time in neighboring time zones differs by one hour. The boundaries of the belts are drawn taking into account political, administrative and economic boundaries.

The zero belt is considered to be the Greenwich belt (named after the Greenwich Observatory near London), which runs on both sides of the prime meridian. The time of the prime, or prime, meridian is considered Universal time.

Meridian 180° is taken as international date line- a conventional line on the surface of the globe, on both sides of which the hours and minutes coincide, and the calendar dates differ by one day.

For a more rational use of daylight in summer, in 1930, our country introduced maternity time, one hour ahead of the time zone. To achieve this, the clock hands were moved forward one hour. In this regard, Moscow, being in the second time zone, lives according to the time of the third time zone.

Since 1981, from April to October, time has been moved forward one hour. This is the so called summer time. It is introduced to save energy. In summer, Moscow is two hours ahead of standard time.

The time of the time zone in which Moscow is located is Moscow.

Movement of the Earth around the Sun

Rotating around its axis, the Earth simultaneously moves around the Sun, going around the circle in 365 days 5 hours 48 minutes 46 seconds. This period is called astronomical year. For convenience, it is believed that there are 365 days in a year, and every four years, when 24 hours out of six hours “accumulate”, there are not 365, but 366 days in a year. This year is called leap year and one day is added to February.

The path in space along which the Earth moves around the Sun is called orbit(Fig. 4). The Earth's orbit is elliptical, so the distance from the Earth to the Sun is not constant. When the Earth is in perihelion(from Greek peri- near, near and helios- Sun) - the point of orbit closest to the Sun - on January 3, the distance is 147 million km. It is winter in the Northern Hemisphere at this time. Greatest distance from the Sun in aphelion(from Greek aro- away from and helios- Sun) - greatest distance from the Sun - July 5th. It is equal to 152 million km. It's summer in the Northern Hemisphere at this time.

Rice. 4. The movement of the Earth around the Sun

The annual movement of the Earth around the Sun is observed by the continuous change in the position of the Sun in the sky - the midday altitude of the Sun and the position of its sunrise and sunset change, the duration of the light and dark parts of the day changes.

When moving in orbit, the direction of the earth's axis does not change; it is always directed towards the North Star.

As a result of changes in the distance from the Earth to the Sun, as well as due to the inclination of the Earth's axis to the plane of its movement around the Sun, an uneven distribution of solar radiation is observed on Earth throughout the year. This is how the change of seasons occurs, which is characteristic of all planets whose axis of rotation is tilted to the plane of its orbit. (ecliptic) different from 90°. The orbital speed of the planet in the Northern Hemisphere is higher in winter and lower in summer. Therefore, the winter half-year lasts 179 days, and the summer half-year - 186 days.

As a result of the Earth's movement around the Sun and the tilt of the Earth's axis to the plane of its orbit by 66.5°, our planet experiences not only a change of seasons, but also a change in the length of day and night.

The rotation of the Earth around the Sun and the change of seasons on Earth are shown in Fig. 81 (equinoxes and solstices in accordance with the seasons in the Northern Hemisphere).

Only twice a year - on the days of the equinox, the length of day and night throughout the Earth is almost the same.

Equinox- the moment in time at which the center of the Sun, during its apparent annual movement along the ecliptic, crosses the celestial equator. There are spring and autumn equinoxes.

The tilt of the Earth's rotation axis around the Sun on the days of the equinoxes March 20-21 and September 22-23 turns out to be neutral with respect to the Sun, and the parts of the planet facing it are evenly illuminated from pole to pole (Fig. 5). The sun's rays fall vertically at the equator.

The longest day and shortest night occur on the summer solstice.

Rice. 5. Illumination of the Earth by the Sun on the days of the equinox

Solstice- the moment the center of the Sun passes the points of the ecliptic most distant from the equator (solstice points). There are summer and winter solstices.

On the day of the summer solstice, June 21-22, the Earth occupies a position in which the northern end of its axis is tilted towards the Sun. And the rays fall vertically not on the equator, but on the northern tropic, the latitude of which is 23°27". Not only the polar regions are illuminated around the clock, but also the space beyond them up to a latitude of 66°33" (the Arctic Circle). In the Southern Hemisphere at this time, only that part of it that lies between the equator and the southern Arctic Circle (66°33") is illuminated. Beyond it, the earth's surface is not illuminated on this day.

On the day of the winter solstice, December 21-22, everything happens the other way around (Fig. 6). The sun's rays are already falling vertically on the southern tropics. The areas that are illuminated in the Southern Hemisphere are not only between the equator and the tropics, but also around the South Pole. This situation continues until the spring equinox.

Rice. 6. Illumination of the Earth on the winter solstice

On two parallels of the Earth on the days of the solstices, the Sun at noon is directly above the observer’s head, i.e. at the zenith. Such parallels are called the tropics. In the Northern Tropic (23° N) the Sun is at its zenith on June 22, in the Southern Tropic (23° S) - on December 22.

At the equator, day is always equal to night. The angle of incidence of the sun's rays on the earth's surface and the length of the day there change little, so the change of seasons is not pronounced.

Arctic Circles remarkable in that they are the boundaries of areas where there are polar days and nights.

Polar day- the period when the Sun does not fall below the horizon. The farther the pole is from the Arctic Circle, the longer the polar day. At the latitude of the Arctic Circle (66.5°) it lasts only one day, and at the pole - 189 days. In the Northern Hemisphere, at the latitude of the Arctic Circle, the polar day is observed on June 22, the day of the summer solstice, and in the Southern Hemisphere, at the latitude of the Southern Arctic Circle, on December 22.

polar night lasts from one day at the latitude of the Arctic Circle to 176 days at the poles. During the polar night, the Sun does not appear above the horizon. In the Northern Hemisphere at the latitude of the Arctic Circle, this phenomenon is observed on December 22.

It is impossible not to note such a wonderful natural phenomenon as white nights. White Nights- these are bright nights at the beginning of summer, when the evening dawn converges with the morning and twilight lasts all night. They are observed in both hemispheres at latitudes exceeding 60°, when the center of the Sun at midnight falls below the horizon by no more than 7°. In St. Petersburg (about 60° N) white nights last from June 11 to July 2, in Arkhangelsk (64° N) - from May 13 to July 30.

The seasonal rhythm in connection with the annual movement primarily affects the illumination of the earth's surface. Depending on the change in the height of the Sun above the horizon on Earth, there are five lighting zones. The hot zone lies between the Northern and Southern tropics (Tropic of Cancer and Tropic of Capricorn), occupies 40% of the earth's surface and is distinguished by the largest amount of heat coming from the Sun. Between the tropics and the Arctic Circles in the Southern and Northern Hemispheres there are moderate light zones. The seasons of the year are already pronounced here: the further from the tropics, the shorter and cooler the summer, the longer and colder the winter. The polar zones in the Northern and Southern Hemispheres are limited by the Arctic Circles. Here the height of the Sun above the horizon is low throughout the year, so the amount of solar heat is minimal. The polar zones are characterized by polar days and nights.

Depending on the annual movement of the Earth around the Sun, not only the change of seasons and the associated unevenness of illumination of the earth’s surface across latitudes, but also a significant part of the processes in the geographical envelope: seasonal changes in weather, the regime of rivers and lakes, rhythms in the life of plants and animals, types and timing of agricultural work.

Calendar.Calendar- a system for calculating long periods of time. This system is based on periodic natural phenomena associated with the movement of celestial bodies. The calendar uses astronomical phenomena - the change of seasons, day and night, and changes in lunar phases. The first calendar was Egyptian, created in the 4th century. BC e. On January 1, 45, Julius Caesar introduced the Julian calendar, which is still used by the Russian Orthodox Church. Due to the fact that the length of the Julian year is 11 minutes 14 seconds longer than the astronomical one, by the 16th century. an “error” of 10 days accumulated - the day of the vernal equinox did not occur on March 21, but on March 11. This error was corrected in 1582 by decree of Pope Gregory XIII. The counting of days was moved forward 10 days, and the day after October 4 was prescribed to be considered Friday, but not October 5, but October 15. The vernal equinox was again returned to March 21, and the calendar began to be called the Gregorian calendar. It was introduced in Russia in 1918. However, it also has a number of disadvantages: unequal length of months (28, 29, 30, 31 days), inequality of quarters (90, 91, 92 days), inconsistency of the numbers of months by day of the week.

For billions of years, day after day, the Earth rotates around its axis. This makes sunrises and sunsets commonplace for life on our planet. The Earth has been doing this since it formed 4.6 billion years ago. And will continue to do this until it ceases to exist. This will probably happen when the Sun turns into a red giant and swallows our planet. But why Earth?

Why does the Earth rotate?

The Earth was formed from a disk of gas and dust that revolved around the newborn Sun. Thanks to this spatial disk, dust and rock particles fell together to form the Earth. As the Earth grew, space rocks continued to collide with the planet. And they had an effect on it that made our planet rotate. And since all the debris in the early Solar System orbited the Sun in roughly the same direction, the collisions that caused the Earth (and most other bodies in the Solar System) to spin spun it in that same direction.

Gas and dust disk

A reasonable question arises: why did the gas-dust disk itself rotate? The Sun and the Solar System were formed at the moment when a cloud of dust and gas began to become denser under the influence of its own weight. Most of the gas came together to become the Sun, and the remaining material created the planetary disk surrounding it. Before it took shape, gas molecules and dust particles moved within its boundaries evenly in all directions. But at some point, randomly, some molecules of gas and dust combined their energy in one direction. This established the direction of rotation of the disk. As the gas cloud began to compress, its rotation accelerated. The same process occurs when skaters begin to spin faster if they press their arms closer to their body.

There are not many factors in space that can cause planets to rotate. Therefore, once they begin to rotate, this process does not stop. The rotating young solar system has high angular momentum. This characteristic describes the tendency of an object to continue spinning. It can be assumed that all exoplanets probably also begin to rotate in the same direction around their stars when their planetary system is formed.

And we are spinning in reverse!

It is interesting that in the solar system some planets have a direction of rotation opposite to their movement around the Sun. Venus rotates in the opposite direction relative to the Earth. And the axis of rotation of Uranus is tilted by 90 degrees. Scientists do not fully understand the processes that caused these planets to acquire such rotation directions. But they have some guesses. Venus may have received this rotation as a result of a collision with another cosmic body at an early stage of its formation. Or perhaps Venus began to rotate in the same way as the other planets. But over time, the Sun's gravity began to slow down its rotation due to its dense clouds. Which, combined with friction between the planet's core and its mantle, caused the planet to spin in the other direction.

In the case of Uranus, scientists suggested that the planet collided with a huge rocky debris. Or perhaps with several different objects that changed its axis of rotation.

Despite such anomalies, it is clear that all objects in space rotate in one direction or another.

Everything is spinning

Asteroids rotate. The stars are spinning. According to NASA, galaxies also rotate. It takes the solar system 230 million years to complete one revolution around the center of the Milky Way. Some of the fastest spinning objects in the Universe are dense, round objects called pulsars. They are the remnants of massive stars. Some city-sized pulsars can rotate around their axis hundreds of times per second. The fastest and most famous of them, discovered in 2006 and called Terzan 5ad, rotates 716 times per second.

Black holes can do this even faster. One of them, called GRS 1915+105, is believed to be capable of spinning between 920 and 1,150 times per second.

However, the laws of physics are inexorable. All rotations eventually slow down. When, it rotated around its axis at a rate of one revolution every four days. Today, our star takes about 25 days to complete one revolution. Scientists believe that the reason for this is that the Sun's magnetic field interacts with the solar wind. This is what slows down its rotation.

The Earth's rotation is also slowing down. The Moon's gravity affects the Earth in such a way that it slowly slows down its rotation. Scientists have calculated that the Earth's rotation has slowed down by a total of about 6 hours over the past 2,740 years. This amounts to just 1.78 milliseconds over the course of a century.

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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 in the northern hemisphere to the right, and in the southern hemisphere to the left.

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. 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.
• 22nd of June- 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.

tropical

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 in the northern hemisphere to the right, and in the southern hemisphere to the left.

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.

Consider the rotation of the Earth around the Sun.

• December 22- winter solstice. 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.
• 22nd of June- 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.