The daily rotation of the globe leads to a sequential change of days and nights, and its orbital movement leads to the alternation of seasons and the change of the years themselves. These movements are the most important for earthlings, because they underlie astronomical methods of measuring time, but they are far from the only ones. Rushing along the solar orbit at an average speed of about 30 km/s, our Earth also makes many other very diverse movements.
As already mentioned, the Earth’s rotation axis maintains a constant position in space throughout the year, that is, it remains parallel to itself. And the northern end of this axis is directed towards a fixed point in the sky near the North Star. And yet this is not entirely true. From century to century, the earth's axis, like the axis of a rotating top, slowly describes a cone, and this movement is caused by the same forces as sea tides - the attraction of the Moon and the Sun. Only in this case they affect not the waters of the oceans, but the masses of the Earth that form its equatorial swelling.
As a result of changes in the direction of the earth's axis in space, the poles of the world slowly move among the stars in a small circle with a radius of 23 degrees 26 minutes of arc. It is at this angle that the Earth’s rotation axis is tilted from the perpendicular to the plane of the Earth’s orbit (the ecliptic plane) and at the same angle the celestial equator is inclined to the ecliptic plane. Let us remind you: the celestial equator is a large circle located 90 degrees from the poles of the world. It intersects with the ecliptic at the points of the spring and autumn equinox. And as soon as the celestial pole moves, the equinox points slowly move along the ecliptic towards the apparent movement of the Sun. As a result, spring arrives every year 20 minutes and 24 seconds earlier than the Sun manages to circle the entire ecliptic. Hence this phenomenon got its name precession, which translated from Latin means “walking forward”, or anticipation of the equinoxes.
Calculations have shown that the celestial pole makes a full circle on the celestial sphere in 25,770 years, that is, for almost 258 centuries. It is currently located approximately 46 arcminutes from Polaris. In 2103, it will approach the guiding star at a minimum distance of 27 arc minutes, and then, moving in the direction of the constellation Cepheus, it will slowly move away from it.
For a long time, the North Pole of the world will not be “marked” by any bright star and only around 7500 will it pass at a distance of 2 degrees from Alpha Cephei - a star of the second magnitude, rivaling Polaris in its brilliance. Around 13,600, the brightest star in the northern sky, Vega, will act as a guiding light. Finally, the hour will come when, due to the further movement of the celestial pole, the royal Sirius will disappear from the skies of northern latitudes, but the constellation of the Southern Cross will be visible.
Precession is complicated by the so-called nutation- slight swaying of the earth's axis. Like precession, it comes from the influence of our satellite on the equatorial swelling of the globe. As a result of the addition of these two movements, the movement of the celestial pole occurs not just in a circle, but along a slightly wavy curve. This is the fourth movement of the Earth.
The inclination of the Earth's rotation axis to the orbital plane does not remain unchanged. Our planet, although very slowly, still “sways”, that is, the tilt of the earth’s axis changes slightly. It is currently decreasing by about 0.5 arcseconds per year. If this decrease occurred continuously, then somewhere in the year 177,000, earthlings would have an excellent opportunity to live on a planet with a perpendicular axis. What changes would then occur in nature? On a globe with a perpendicular axis there would no longer be any change of seasons. Its inhabitants could enjoy eternal spring! However, the range of fluctuations in the inclination of the Earth's rotation axis is very small - it does not exceed 2-3 degrees. The current “straightening” of the earth’s axis will definitely stop, after which its tilt will increase.
Recall that the earth's orbit is an ellipse. And the shape of this ellipse is also subject to slow changes. It becomes more or less elongated. Currently, the eccentricity of the earth's ellipse is 0.0167, and in 24,000 the earth's orbit will turn almost into a circle. Then, over the course of 40 thousand years, the eccentricity will begin to increase again, and this will continue, apparently, as long as our planet itself exists. It's permanent change in the eccentricity of the earth's orbit can be considered as the sixth movement of the Earth.
The planets also do not leave the Earth alone. Depending on their mass and distance, they have a very noticeable effect on it. Thus, the major axis of the earth's orbit, connecting the closest and most distant points of the earth's path from the sun (perihelion and aphelion), rotates slowly due to the combined gravity of the planets. This cycle, lasting 21 thousand years, is secular perihelion change and is the seventh movement of the Earth.
As a result of changes in the orientation of the Earth's orbit, the timing of the Earth's passage through perihelion slowly changes. And if now the Earth passes through perihelion in early January, then around 11,900 it will be at perihelion on the days of the summer solstice: winters will then be especially cold, and summer heat will reach its highest limit.
Popular astronomy books say that “the moon revolves around the earth,” but this expression is not entirely accurate. The fact is that not only the Earth attracts the Moon, but the Moon also attracts the Earth, and both celestial bodies move together, as one, around the common center of mass of the Earth-Moon system. The mass of the Moon is 81.3 times less than the mass of the Earth, and therefore this center is 81.3 times closer to the center of the Earth than to the center of the Moon. The average distance between their centers is 384,400 km. Using these data, we obtain: the center of mass of the Earth-Moon system is located at a distance of 4671 km from the center of the Earth towards the Moon, that is, at a distance of 1707 km below the surface of the Earth (the equatorial radius of the Earth is 6378 km). It is around this center that the Earth and the Moon describe their orbits during the month. As a result, the Earth monthly either approaches the Sun or moves away from it, which causes slight changes in the apparent diameter of the daylight. This is the eighth movement of the Earth.
Strictly speaking, the center of mass of the Earth-Moon system moves in circumsolar orbit. Therefore, the Earth's trajectory should look like a slightly wavy line.
If only one Earth revolved around the Sun, then both celestial bodies would describe ellipses around the common center of mass of the Sun-Earth system. But the attraction of the Sun by other large planets forces this center to describe a very complex curve. And when all the planets are located on one side of the central body, they attract it especially strongly and displace the Sun, causing the center of mass of the entire solar system to extend beyond the solar globe. This is how another, ninth complication arises in the movement of the Earth.
Finally, our Earth itself easily responds to the attraction of other planets in the solar system. Indeed, according to Newton's law, all celestial bodies are attracted to one another with a force directly proportional to the product of their masses and inversely proportional to the square of their distance. This influence of the planets does not manifest itself in the best way - it deflects the Earth from its elliptical path around the Sun (from the Keplerian orbit) and causes all those irregularities in its orbital motion, which are called disturbances or perturbations. The greatest disturbance to the Earth is caused by the massive giant Jupiter and our neighbor Venus. The complication of the trajectory of the Earth's movement under the influence of the gravity of the planets constitutes its tenth movement.
It has long been established that stars move through space at enormous speeds. Our Sun is no exception. Relative to the nearest stars, it flies in the direction of the constellation Hercules at a speed of about 20 km/s, carrying with it all its satellites, including the Earth. The movement of the Earth in space caused by the translational movement of the Sun is the eleventh movement of our planet. Thanks to this endless flight, we forever leave the region of the sky where Sirius shines, and approach the unknown depths of the stars, where Vega sparkles brightly. Since the Earth was formed, it has never flown through familiar places and will never return to the point in the Universe where we are at the moment.
Let us depict the direction of the Sun's movement in space as a straight arrow. Then the point in the sky to which it flies will make an angle of about 40 degrees with the pole of the ecliptic. As we see, our central luminary moves completely obliquely (relative to the ecliptic plane), and the Earth, like a hawk or eagle, describes a giant spiral around it...
If we could look at our galactic stellar “island” from the outside and recognize our Sun among 200 billion stars, we would establish that it moves around the center of the Galaxy at a speed of about 220 km/s and completes its path in about 230 million years . The entire solar system participates in this rapid flight around the galactic core along with the Sun, and for our Earth this is the twelfth movement.
The flight of the Earth together with the Sun around the core of the Galaxy is complemented by the thirteenth movement of our entire stellar system relative to the center of the cluster of galaxies closest to us.
It should be noted that the listed thirteen movements of the Earth do not exhaust all of its possible movements. In the Universe, every celestial body must participate in many different relative motions.
Many of the features of life familiar to us since childhood are the result of processes on a cosmic scale. The change of day and night, seasons, the duration of the period during which the Sun is above the horizon are associated with how and at what speed the Earth rotates, with the peculiarities of its movement in space.
Imaginary line
The axis of any planet is a speculative construction, created for the convenience of describing movement. If you mentally draw a line through the poles, this will be the Earth's axis. Rotation around it is one of the two main movements of the planet.
The axis does not make 90º with the plane of the ecliptic (the plane around the Sun), but deviates from the perpendicular by 23º27". It is believed that the planet rotates from west to east, that is, counterclockwise. This is exactly what its movement around the axis looks like when observed in the North pole.
Irrefutable proof
It was once believed that our planet was stationary, and the stars fixed in the sky revolved around it. For quite a long time in history, no one was interested in the speed at which the Earth revolves in orbit or around its axis, since the very concepts of “axis” and “orbit” did not fit into the scientific knowledge of that period. Experimental proof of the fact that the Earth is constantly moving around its axis was obtained in 1851 by Jean Foucault. It finally convinced everyone who still doubted this in the century before last.
The experiment was carried out under a dome in which a pendulum and a circle with divisions were placed. Swinging, the pendulum shifted several notches with each new movement. This is only possible if the planet rotates.
Speed
How fast does the Earth rotate on its axis? It is quite difficult to give an unambiguous answer to this question, since the speed of different geographical points is not the same. The closer the area is to the equator, the higher it is. In the Italian region, the speed value, for example, is estimated at 1200 km/h. On average, the planet travels 15º in an hour.
The length of the day is related to the speed of the Earth's rotation. The length of time during which our planet makes one revolution around its axis is determined in two ways. To determine the so-called sidereal or sidereal day, any star other than the Sun is selected as a reference system. They last 23 hours 56 minutes and 4 seconds. If our luminary is taken as the starting point, then the day is called solar. Their average duration is 24 hours. It varies somewhat depending on the position of the planet relative to the star, which affects both the speed of rotation around its axis and the speed at which the Earth rotates in orbit.
Around the center
The second most important movement of the planet is its “circling” in orbit. Constant movement along a slightly elongated trajectory is felt by people most often due to the change of seasons. The speed at which the Earth moves around the Sun is expressed for us primarily in units of time: one revolution takes 365 days 5 hours 48 minutes 46 seconds, that is, an astronomical year. The exact figure clearly explains why every four years there is an extra day in February. It represents the sum of hours accumulated during this time that were not included in the accepted 365 days of the year.
Trajectory Features
As already noted, the speed at which the Earth rotates in orbit is associated with the characteristics of the latter. The planet's trajectory differs from an ideal circle; it is slightly elongated. As a result, the Earth either approaches the star or moves away from it. When the planet and the Sun are separated by a minimum distance, this position is called perihelion. The maximum distance corresponds to aphelion. The first falls on January 3, the second on July 5. And for each of these points the question: “At what speed does the Earth rotate in orbit?” - has its own answer. For aphelion it is 29.27 km/s, for perihelion it is 30.27 km/s.
Length of day
The speed at which the Earth rotates in its orbit, and in general the movement of the planet around the Sun, have a number of consequences that determine many of the nuances of our lives. For example, these movements affect the length of the day. The sun constantly changes its position in the sky: the points of sunrise and sunset shift, and the height of the star above the horizon at noon becomes slightly different. As a result, the length of day and night changes.
These two values coincide only at the equinox, when the center of the Sun crosses the celestial equator. The tilt of the axis turns out to be neutral with respect to the star, and its rays fall vertically onto the equator. The spring equinox falls on March 20-21, the autumn equinox on September 22-23.
Solstice
Once a year a day reaches its maximum length, and six months later it reaches its minimum. These dates are usually called solstice. Summer falls on June 21-22, and winter falls on December 21-22. In the first case, our planet is positioned in such a way in relation to the star that the northern edge of the axis looks in the direction of the Sun. As a result, the rays fall vertically onto and illuminate the entire region beyond the Arctic Circle. In the Southern Hemisphere, on the contrary, the sun's rays reach only the area between the equator and the Arctic Circle.
During the winter solstice, events proceed in exactly the same way, only the hemispheres change roles: the South Pole is illuminated.
Seasons
Orbital position affects more than just how fast the Earth moves around the Sun. As a result of changes in the distance separating it from the star, as well as the tilt of the planet’s axis, solar radiation is distributed unevenly throughout the year. And this, in turn, causes the change of seasons. Moreover, the duration of the winter and summer half-years is different: the first is 179 days, and the second - 186. This discrepancy is caused by the same tilt of the axis relative to the plane of the ecliptic.
Light belts
The Earth's orbit has another consequence. The annual movement leads to a change in the position of the Sun above the horizon, as a result of which belts of illumination are formed on the planet:
Hot regions are located on 40% of the Earth's territory, between the Southern and Northern Tropics. As the name suggests, this is where most of the heat comes.
Temperate zones - between the Arctic Circle and the Tropics - are characterized by a pronounced change of seasons.
The polar zones, located beyond the Arctic Circles, are characterized by low temperatures throughout the year.
The movement of the planets in general and, in particular, the speed at which the Earth orbits, also influence other processes. Among them are the flow of rivers, the change of seasons, and certain rhythms of life of plants, animals and humans. In addition, the rotation of the Earth, due to its influence on illumination and surface temperature, affects agricultural work.
Today, what is the speed of rotation of the Earth, what is its distance to the Sun, and other features related to the movement of the planet are studied in school. However, if you think about it, they are not at all obvious. When such a thought comes to mind, I would like to sincerely thank those scientists and researchers who, largely thanks to their extraordinary minds, were able to discover the laws of the cosmic life of the Earth, describe them, and then prove and explain them to the rest of the world.
Hello dear readers! Today I would like to touch on the topic of the Earth and, and I thought that a post about how the Earth rotates would be useful to you 🙂 After all, day and night, and also the seasons, depend on this. Let's take a closer look at everything.
Our planet rotates around its axis and around the Sun. When it makes one revolution around its axis, one day passes, and when it revolves around the Sun, one year passes. Read more about this below:
Earth's axis.
Earth's axis (Earth's rotation axis) – this is the straight line around which the Earth’s daily rotation occurs; this line passes through the center and intersects the surface of the Earth.
The tilt of the Earth's rotation axis.
The Earth's rotation axis is inclined to the plane at an angle of 66°33´; thanks to this it happens. When the Sun is above the Tropic of the North (23°27´ N), summer begins in the Northern Hemisphere, and the Earth is at its farthest distance from the Sun.
When the Sun rises above the Tropic of South (23°27´ S), summer begins in the Southern Hemisphere.
In the Northern Hemisphere, winter begins at this time. The attraction of the Moon, Sun and other planets does not change the angle of inclination of the earth's axis, but causes it to move along a circular cone. This movement is called precession.
The North Pole now points toward the North Star. Over the next 12,000 years, as a result of precession, the Earth's axis will travel approximately halfway and will be directed towards the star Vega.
About 25,800 years constitute a complete precessional cycle and significantly influence the climate cycle.
Twice a year, when the Sun is directly above the equator, and twice a month, when the Moon is in a similar position, the attraction due to precession decreases to zero and there is a periodic increase and decrease in the rate of precession.
Such oscillatory movements of the earth's axis are known as nutation, which peaks every 18.6 years. In terms of the significance of its influence on climate, this periodicity ranks second after changes in seasons.
The rotation of the Earth around its axis.
Daily rotation of the Earth - the movement of the Earth counterclockwise, or from west to east, as viewed from the North Pole. The rotation of the Earth determines the length of the day and causes the change between day and night.
The Earth makes one revolution around its axis in 23 hours 56 minutes and 4.09 seconds. During the period of one revolution around the Sun, the Earth approximately makes 365 ¼ revolutions, this is one year or equal to 365 ¼ days.
Every four years, another day is added to the calendar, because for each such revolution, in addition to a whole day, another quarter of a day is spent. The Earth's rotation gradually slows down the Moon's gravitational pull, lengthening the day by about 1/1000th of a second every century.
Judging by geological data, the rate of rotation of the Earth could change, but by no more than 5%.
Around the Sun, the Earth rotates in an elliptical orbit, close to circular, at a speed of about 107,000 km/h in the direction from west to east. The average distance to the Sun is 149,598 thousand km, and the difference between the smallest and largest distance is 4.8 million km.
The eccentricity (deviation from the circle) of the Earth's orbit changes slightly over the course of a cycle lasting 94 thousand years. It is believed that the formation of a complex climate cycle is facilitated by changes in the distance to the Sun, and the advance and retreat of glaciers during ice ages are associated with its individual stages.
Everything in our vast Universe is arranged very complexly and precisely. And our Earth is just a point in it, but this is our home, which we learned a little more about from the post about how the Earth rotates. See you in new posts about the study of the Earth and the Universe🙂
Like other planets of the solar system, it makes 2 main movements: around its own axis and around the Sun. Since ancient times, it was on these two regular movements that time calculations and the ability to compile calendars were based.
A day is the time of rotation around its own axis. A year is a revolution around the Sun. The division into months is also in direct connection with astronomical phenomena - their duration is related to the phases of the Moon.
Rotation of the Earth around its own axis
Our planet rotates around its own axis from west to east, that is, counterclockwise (when viewed from the North Pole.) An axis is a virtual straight line crossing the globe in the area of the North and South Poles, i.e. the poles have a fixed position and do not participate in rotational motion, while all other location points on the earth's surface rotate, and the rotation speed is not identical and depends on their position relative to the equator - the closer to the equator, the higher the rotation speed.
For example, in the Italian region the rotation speed is approximately 1200 km/h. The consequences of the Earth's rotation around its axis are the change of day and night and the apparent movement of the celestial sphere.
Indeed, it seems that the stars and other celestial bodies of the night sky are moving in the opposite direction to our movement with the planet (that is, from east to west).
It seems that the stars are around the North Star, which is located on an imaginary line - a continuation of the earth's axis in a northerly direction. The movement of stars is not proof that the Earth rotates around its axis, because this movement could be a consequence of the rotation of the celestial sphere, if we assume that the planet occupies a fixed, motionless position in space.
Foucault pendulum
Irrefutable proof that the Earth rotates on its own axis was presented in 1851 by Foucault, who conducted the famous experiment with a pendulum.
Let's imagine that, being at the North Pole, we set a pendulum into oscillatory motion. The external force acting on the pendulum is gravity, but it does not affect the change in the direction of oscillations. If we prepare a virtual pendulum that leaves marks on the surface, we can make sure that after some time the marks will move in a clockwise direction.
This rotation can be associated with two factors: either with the rotation of the plane on which the pendulum makes oscillatory movements, or with the rotation of the entire surface.
The first hypothesis can be rejected, taking into account that there are no forces on the pendulum that can change the plane of oscillatory movements. It follows that it is the Earth that rotates, and it makes movements around its own axis. This experiment was carried out in Paris by Foucault, he used a huge pendulum in the form of a bronze sphere weighing about 30 kg, suspended from a 67-meter cable. The starting point of the oscillatory movements was recorded on the surface of the floor of the Pantheon.
So, it is the Earth that rotates, and not the celestial sphere. People observing the sky from our planet record the movement of both the Sun and planets, i.e. All objects in the Universe move.
Time criterion – day
A day is the period of time during which the Earth makes a complete revolution around its own axis. There are two definitions of the concept “day”. A “solar day” is a period of time of the Earth’s rotation, during which . Another concept - “sidereal day” - implies a different starting point - any star. The duration of the two types of days is not identical. The length of a sidereal day is 23 hours 56 minutes 4 seconds, while the length of a solar day is 24 hours.
The different durations are due to the fact that the Earth, rotating around its own axis, also performs an orbital rotation around the Sun.
In principle, the length of a solar day (although it is taken as 24 hours) is not a constant value. This is due to the fact that the Earth's orbital movement occurs at a variable speed. When the Earth is closer to the Sun, its orbital speed is higher; as it moves away from the sun, the speed decreases. In this regard, such a concept as “average solar day” was introduced, namely its duration is 24 hours.
Orbiting the Sun at a speed of 107,000 km/h
The speed of the Earth's revolution around the Sun is the second main movement of our planet. The Earth moves in an elliptical orbit, i.e. the orbit has the shape of an ellipse. When it is in close proximity to the Earth and falls into its shadow, eclipses occur. The average distance between the Earth and the Sun is approximately 150 million kilometers. Astronomy uses a unit to measure distances within the solar system; it is called the “astronomical unit” (AU).
The speed at which the Earth moves in orbit is approximately 107,000 km/h.
The angle formed by the earth's axis and the plane of the ellipse is approximately 66°33', this is a constant value.
If you observe the Sun from Earth, you get the impression that it is the Sun that moves across the sky throughout the year, passing through the stars and stars that make up the Zodiac. In fact, the Sun also passes through the constellation Ophiuchus, but it does not belong to the Zodiac circle.
Our planet is in constant motion, it rotates 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 relative to the plane of the Earth. People cannot notice the moment of rotation, because all objects move 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 revolution around the axis is completed within one sidereal day, consisting of 23 hours 56 minutes and 4 seconds. During this period, first one or the other side of the planet turns towards the Sun, receiving different amounts of heat and light from it. In addition, the rotation of the Earth around its axis affects its shape (flattened poles are the result of the planet’s rotation around its axis) and the deviation when bodies move in the horizontal plane (rivers, currents and winds of the Southern Hemisphere deviate to the left, of the Northern Hemisphere to the right).
Linear and angular rotation speed
(Earth Rotation)
The linear speed of rotation of the Earth around its axis is 465 m/s or 1674 km/h in the equator zone; as you move away from it, the speed gradually slows down, at the North and South Poles it is zero. For example, for citizens of the equatorial city of Quito (the capital of Ecuador in South America), the rotation speed is exactly 465 m/s, and for Muscovites living at the 55th parallel north of the equator, it is 260 m/s (almost half as much) .
Every year, the speed of rotation around the axis decreases by 4 milliseconds, which is due to the influence of the Moon on the strength of sea and ocean tides. The Moon's gravity "pulls" the water in the opposite direction to the Earth's axial rotation, creating a slight frictional force that slows the rotation speed by 4 milliseconds. The speed of angular rotation remains the same everywhere, its value is 15 degrees per hour.
Why does day give way to night?
(Change of day and night)
The time for a complete revolution 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 under the control 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, on the contrary, frost would be raging 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 tilted relative to the earth's surface at a certain angle, its parts receive different amounts of heat and light at different times, which causes the change of seasons. According to the astronomical parameters necessary to determine the time of year, certain points in time are taken as reference points: for summer and winter these are the Solstice Days (June 21 and December 22), for spring and autumn - the Equinoxes (March 20 and September 23). From September to March, the Northern Hemisphere faces the Sun for less time and, accordingly, receives less heat and light, hello winter-winter, the Southern Hemisphere receives a lot of heat and light at this time, long live summer! 6 months pass and the Earth moves to the opposite point of its orbit and the Northern Hemisphere receives more heat and light, the days become longer, the Sun rises higher - summer comes.
If the Earth were located in relation to the Sun in an exclusively 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.
