Why do planets rotate around their axis? Why does the Earth rotate? Why does the Moon revolve around the Earth

The movement of the planet in orbit is determined by two reasons:
- linear inertia of motion (it tends to rectilinear - tangential)
and the gravitational force of the Sun.

It is the force of gravity that will change the direction of movement from linear to circular. And gravitational forces applied to a smaller radius will act
stronger on the planet.
If we consider gravity as a force applied to the center, then this gives a change in the direction of movement to a circular one.
If we consider gravity as the sum of forces applied to the entire mass of the planet,
then this gives both a change in the motion vector to a circular one and rotation around an axis.

Look at the picture.
The planet has points located closer to the Sun and points more distant.
Point A will be closer to the Sun than point B.
And the attraction of point A will be greater than that of point B. Recall that the force of gravity depends on the radius squared.
When the planet moves clockwise, the gravitational force through point A will pull the planet away more than through point B. This difference in gravitational forces applied to diametrically opposite points of the planet, with simultaneous movement, creates rotation.

Thus, the period of revolution of the planet around its axis directly depends on the equatorial radius of the planet.
With large planets such as Jupiter and Saturn, the difference in the attraction of opposite points is greater and the planet rotates faster.

Table of solar days for planets and equatorial radius:
t r
Mercury..... - 175.9421 .... - 0.3825
Venus..... - 116.7490 .....-0.9488
Earth...... - 1.0 .... .. - 1.0
M a r s.... - 1.0275 ... ... - 0.5326
Jupiter..... - 0.41358 ... - 11.209
Saturn..... - 0.44403 .... - 9.4491
U r a n..... - 0.71835 ... - 4.0073
Neptune..... - 0.67126 ... - 3.8826
Pluto..... - 6.38766 .... - 0.1807

The first number is the period of rotation of the planet around its axis in Earth days, the second number is similar - the equatorial radius of the planet. And it is clear that the largest planet, Jupiter, rotates the fastest, and the smallest, Mercury, rotates the slowest.

In general, the reason for the rotation of the Earth can be explained simply.
As the planet moves in orbit, there is a constant change in the direction of its motion from straight to circular. And at the same time, a simultaneous rotation of the planet occurs, due to the fact that the points of attraction of planets located closer to the Sun will pull the planet more strongly than those further away.

For example, on Jupiter, where the planet is not a monolith, rotation occurs in layers. The equatorial movement of the layers is especially noticeable.

Reviews

Dear Nikolai!
There is no gravity. Newton's and Einstein's laws do not work.
Using such methods, it is impossible to substantiate the causes of rotation.
But the topic is interesting.
I hope that through joint efforts, and not on this site, we will solve it.

No. Gravity is all there! But we have not yet established the reasons for its appearance.
“Gravitational force,” a term conventionally accepted hereinafter, means an external influence on the body. Conventionally, in physics this is called the “force” of gravity.

And rotation occurs from the action of two forces: the inertia of rectilinear motion and its change to circular motion under the influence of the force of gravity, which in vector is perpendicular to the vector of inertia.

Dear Nikolai!

Dear Nikolai!
Your works already contain calculations, I won’t say, that substantiate the absence of gravity. These works aroused my interest in you, because it is clear that there is a large statistical material and on it, together and quickly we will build a science for ourselves, where many things will fall into place. And whether they accept it or not, it shouldn’t concern us. Let Volosatov prove it, and we will do it.

I can formulate my position on gravity like this.
Gravity, as an attractive force that arises between two bodies, does not exist.
There is an external influence on bodies, the consequence of which is the appearance of force, causing them to move towards each other. Force does not lead to the appearance of another force, but to movement. In this case, the vector of this force is directed along the line connecting these two bodies.
Not attraction, but movement towards.
And not the force arising in the bodies themselves, but the force of external influence.
Like the wind blows on a sail.
In general, I understand force as a factor of external influence.

Dear Nikolai!
Having refuted the forces and their reactions, you return to them again.
Yes, these are the “weights” of our teachings. It’s difficult to break away from them. I am still tearing myself away from the remnants of the teachings of the “institute”. But the physics of the world is completely different. You intuitively felt it. The rest is in personal correspondence.

Today no one has any doubts about the fact that the Earth rotates both around its axis and around the Sun, our natural luminary. This is an absolute and proven fact, but why does the Earth spin the way it does? We will look into this issue today.

Why does the Earth spin on its axis?

We will start with the very first question, which is the nature of the independent rotation of our planet.

And the answer to this question, like many other questions about the secrets of our universe, is the Sun. It is the impact of the Sun's rays on our planet that sets it in motion. If we delve a little deeper into this issue, it is worth noting that the sun's rays warm the atmosphere and hydrosphere of the planet, which are set in motion during the heating process. This movement is what makes the Earth move.

As for the answer to the question of why the Earth rotates counterclockwise and not clockwise, there is no factual confirmation of this fact as such. However, it is worth noting that most bodies in our solar system rotate precisely in a counterclockwise direction. That is why this condition also affected our planet.

In addition, it is important to understand that the Earth rotates counterclockwise only if its movement is observed from the north pole. In the case of observations from the south pole, rotations will occur differently - clockwise.

Why does the Earth revolve around the Sun

As for the more global issue related to the rotation of our planet around its natural star, we examined it in as much detail as possible within the framework of the corresponding article on our website. However, in short, the reason for this rotation is the law of universal gravitation, which acts in Space as on Earth. And it lies in the fact that bodies with greater mass attract less “weighty” bodies. Thus, the Earth is attracted to the Sun and rotates around the star due to its mass, as well as acceleration, moving strictly along the existing orbit.

Why does the Moon revolve around the Earth

We have also already considered the nature of rotation of the natural satellite of our planet, and the reason for such movement is of a similar nature - the law of universal gravitation. The Earth, of course, has more mass than the Moon. Accordingly, the Moon is attracted to the Earth and moves along its orbit.

“And yet she spins!” - this famous phrase of the great Italian astronomer G. Galilei most likely belongs to the realm of legends (it is unlikely that the Holy Inquisition would have allowed him such a formal renunciation), but it will forever remain in the memory of mankind as a kind of monument of what kind of work it took to understand that ours is rotating , and not only around the Sun, but also around its axis. But proving the rotation of the Earth was only the beginning; it was also necessary to explain why this happens!

To find an explanation for this, we will have to travel back to those distant times when the Solar system in general and the Earth in particular were born from a huge cloud of gas and dust. This cloud itself also rotated - without this nothing would have happened, it would have floated in space, remaining only a cloud and nothing else. But the rotation made it shrink, and its constituent particles collided with each other and “huddled together.” At first these were small particles, then large ones were formed from them, continuing to collide with each other, then the same thing happened with fairly large bodies - planetesimals... but no matter the size of the colliding bodies, the impulses of their movement did not go away! The new formation continued to rotate by inertia, receiving additional momentum from the collision of bodies merging with each other.

Collisions with large objects could also affect the rotation of already “ready” (or almost “ready”) planets. For example, Venus rotates differently from all other planets - in the opposite direction, and Uranus generally rotates, “lying on its side,” i.e. its axis of rotation differs only slightly from the orbital plane. Scientists suggest that this is due to collisions with large objects that took place during the “youth” of the Solar System, when there were an order of magnitude more planets, and many of them moved in emergency orbits (i.e., in such orbits that made collisions inevitable ). In this regard, we were “lucky”: the Earth also survived a collision with a very large planet, approximately the size of Mars (astronomers even gave it a name - Theia), but this did not affect its rotation, at least, it did not affect the way it happened with Venus or Uranus.

However, it would be wrong to say that the collision with Theia had no effect on the Earth’s rotation at all. We received as a souvenir of this big collision our only natural satellite - the Moon, and now it very much influences the rotation of the Earth! The fact is that one celestial body with its gravity is quite capable of slowing down the rotation of another, so the Moon slows down the rotation of the Earth. True, we are talking about fractions of a second per year - but over centuries and millennia, fractions of seconds add up to seconds, seconds to minutes, and minutes to hours! The English astronomer R. Stephenson analyzed the astronomical observations of the sages of Babylon, Egypt and other civilizations of the Ancient World, starting from 700 BC. It turned out that if we were transported in a time machine to 700 BC. at the same time of day, we would have to set the clock to 7 o'clock! An impressive deviation... and in the days when dinosaurs lived, the day was 21 hours long. Why, if there were no Moon, the earth’s day would last only six hours!

However, the speed of rotation of planets is affected not only by the gravity of other bodies, but also by the density of its matter. The closer a planet is to the Sun, the higher its density, which is why small Mercury rotates around its axis much slower than the giant Jupiter.

Our planet is in constant motion. Together with the Sun, it moves in space around the center of the Galaxy. And she, in turn, moves in the Universe. But the rotation of the Earth around the Sun and its own axis plays the greatest importance for all living things. Without this movement, conditions on the planet would be unsuitable for supporting life.

solar system

According to scientists, the Earth as a planet in the solar system was formed more than 4.5 billion years ago. During this time, the distance from the luminary practically did not change. The speed of the planet's movement and the gravitational force of the Sun balanced its orbit. It's not perfectly round, but it's stable. If the gravity of the star had been stronger or the speed of the Earth had noticeably decreased, then it would have fallen into the Sun. Otherwise, sooner or later it would fly into space, ceasing to be part of the system.

The distance from the Sun to the Earth makes it possible to maintain optimal temperature on its surface. The atmosphere also plays an important role in this. As the Earth rotates around the Sun, the seasons change. Nature has adapted to such cycles. But if our planet were at a greater distance, the temperature on it would become negative. If it were closer, all the water would evaporate, since the thermometer would exceed the boiling point.

The path of a planet around a star is called an orbit. The trajectory of this flight is not perfectly circular. It has an ellipse. The maximum difference is 5 million km. The closest point of the orbit to the Sun is at a distance of 147 km. It's called perihelion. Its land passes in January. In July, the planet is at its maximum distance from the star. The greatest distance is 152 million km. This point is called aphelion.

The rotation of the Earth around its axis and the Sun ensures a corresponding change in daily patterns and annual periods.

For humans, the movement of the planet around the center of the system is imperceptible. This is because the mass of the Earth is enormous. Nevertheless, every second we fly about 30 km in space. This seems unrealistic, but these are the calculations. On average, it is believed that the Earth is located at a distance of about 150 million km from the Sun. It makes one full revolution around the star in 365 days. The distance traveled per year is almost a billion kilometers.

The exact distance that our planet travels in a year, moving around the star, is 942 million km. Together with her we move through space in an elliptical orbit at a speed of 107,000 km/hour. The direction of rotation is from west to east, that is, counterclockwise.

The planet does not complete a full revolution in exactly 365 days, as is commonly believed. In this case, about six more hours pass. But for the convenience of chronology, this time is taken into account in total for 4 years. As a result, one additional day “accumulates”; it is added in February. This year is considered a leap year.

The speed of rotation of the Earth around the Sun is not constant. It has deviations from the average value. This is due to the elliptical orbit. The difference between the values is most pronounced at the perihelion and aphelion points and is 1 km/sec. These changes are invisible, since we and all the objects around us move in the same coordinate system.

Change of seasons

The Earth's rotation around the Sun and the tilt of the planet's axis make the seasons possible. This is less noticeable at the equator. But closer to the poles, the annual cyclicity is more pronounced. The northern and southern hemispheres of the planet are heated unevenly by the energy of the Sun.

Moving around the star, they pass four conventional orbital points. At the same time, alternately twice during the six-month cycle they find themselves further or closer to it (in December and June - the days of the solstices). Accordingly, in a place where the surface of the planet warms up better, the ambient temperature there is higher. The period in such a territory is usually called summer. In the other hemisphere it is noticeably colder at this time - it is winter there.

After three months of such movement with a periodicity of six months, the planetary axis is positioned in such a way that both hemispheres are in the same conditions for heating. At this time (in March and September - the days of the equinox) the temperature regimes are approximately equal. Then, depending on the hemisphere, autumn and spring begin.

Earth's axis

Our planet is a rotating ball. Its movement is carried out around a conventional axis and occurs according to the principle of a top. By resting its base on the plane in an untwisted state, it will maintain balance. When the rotation speed weakens, the top falls.

The earth has no support. The planet is affected by the gravitational forces of the Sun, Moon and other objects of the system and the Universe. Nevertheless, it maintains a constant position in space. The speed of its rotation, obtained during the formation of the core, is sufficient to maintain relative equilibrium.

The earth's axis does not pass perpendicularly through the globe of the planet. It is inclined at an angle of 66°33´. The rotation of the Earth around its axis and the Sun makes possible the change of seasons. The planet would “tumble” in space if it did not have a strict orientation. There would be no talk of any constancy of environmental conditions and life processes on its surface.

Axial rotation of the Earth

The rotation of the Earth around the Sun (one revolution) occurs throughout the year. During the day it alternates between day and night. If you look at the Earth's North Pole from space, you can see how it rotates counterclockwise. It completes a full rotation in approximately 24 hours. This period is called a day.

The speed of rotation determines the speed of day and night. In one hour, the planet rotates approximately 15 degrees. The speed of rotation at different points on its surface is different. This is due to the fact that it has a spherical shape. At the equator, the linear speed is 1669 km/h, or 464 m/sec. Closer to the poles this figure decreases. At the thirtieth latitude, the linear speed will already be 1445 km/h (400 m/sec).

Due to its axial rotation, the planet has a somewhat compressed shape at the poles. This movement also “forces” moving objects (including air and water flows) to deviate from their original direction (Coriolis force). Another important consequence of this rotation is the ebb and flow of tides.

the change of night and day

A spherical object is only half illuminated by a single light source at a certain moment. In relation to our planet, in one part of it there will be daylight at this moment. The unlit part will be hidden from the Sun - it is night there. Axial rotation makes it possible to alternate these periods.

In addition to the light regime, the conditions for heating the surface of the planet with the energy of the luminary change. This cyclicality is important. The speed of change of light and thermal regimes is carried out relatively quickly. In 24 hours, the surface does not have time to either heat up excessively or cool down below the optimal level.

The rotation of the Earth around the Sun and its axis at a relatively constant speed is of decisive importance for the animal world. Without a constant orbit, the planet would not remain in the optimal heating zone. Without axial rotation, day and night would last for six months. Neither one nor the other would contribute to the origin and preservation of life.

Uneven rotation

Throughout its history, humanity has become accustomed to the fact that the change of day and night occurs constantly. This served as a kind of standard of time and a symbol of the uniformity of life processes. The period of rotation of the Earth around the Sun is influenced to a certain extent by the ellipse of the orbit and other planets in the system.

Another feature is the change in the length of the day. The Earth's axial rotation occurs unevenly. There are several main reasons. Seasonal variations associated with atmospheric dynamics and precipitation distribution are important. In addition, a tidal wave directed against the direction of the planet’s movement constantly slows it down. This figure is negligible (for 40 thousand years per 1 second). But over 1 billion years, under the influence of this, the length of the day increased by 7 hours (from 17 to 24).

The consequences of the Earth's rotation around the Sun and its axis are being studied. These studies are of great practical and scientific importance. They are used not only to accurately determine stellar coordinates, but also to identify patterns that can influence human life processes and natural phenomena in hydrometeorology and other areas.

It is spherical, however, it is not a perfect ball. 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.

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

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

Rotation of the Earth around the Sun

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

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

December 22- winter solstice. 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.