The path the earth takes to revolve around the sun. What is the name of the planet's rotation around the sun? History of the heliocentric system

Our planet is in constant motion. Together with the Sun, it moves in space around the center of the Galaxy. And that, in turn, moves in the universe. But the most important thing for all living things is the rotation of the Earth around the Sun and its own axis. Without this movement, the conditions on the planet would be unsuitable for sustaining life.

solar system

Earth as a planet of the solar system, according to scientists, was formed more than 4.5 billion years ago. During this time, the distance from the sun practically did not change. The speed of the planet and the gravitational pull of the sun balance its orbit. It is not perfectly round, but stable. If the force of attraction of the star were stronger or the speed of the Earth decreased noticeably, then it would fall on 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 the optimum 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 further away, then 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 round. 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 provides, respectively, a change in daily regimes and annual periods.

For a person, 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 through space about 30 km. It seems unrealistic, but such 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 complete revolution around the star in 365 days. The distance traveled in a year is almost a billion kilometers.

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

The planet does not complete a complete revolution in exactly 365 days, as is commonly believed. It still takes about six hours. But for the convenience of chronology, this time is taken into account in total for 4 years. As a result, one additional day “runs in”, it is added in February. Such a year is considered a leap year.

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

change of seasons

The rotation of the Earth around the Sun and the tilt of the planet's axis make it possible for the seasons to change. It 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 by the energy of the Sun unevenly.

Moving around the star, they pass four conditional points of the orbit. At the same time, twice in turn during the semi-annual cycle, they turn out to be 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 is higher there. The period in such a territory is usually called summer. In the other hemisphere at this time it is noticeably colder - it is winter there.

After three months of such movement, with a frequency of six months, the planetary axis is located 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 come.

earth axis

Our planet is a spinning ball. Its movement is carried out around a conditional axis and occurs according to the principle of a top. Leaning with the base in the plane in the untwisted state, it will maintain balance. When the speed of rotation weakens, the top falls.

The earth has no stop. The forces of attraction of the Sun, the Moon and other objects of the system and the Universe act on the planet. Nevertheless, it maintains a constant position in space. The speed of its rotation, obtained during the formation of the nucleus, is sufficient to maintain relative equilibrium.

The earth's axis passes through the planet's ball is not perpendicular. It is inclined at an angle of 66°33´. The rotation of the Earth on its axis and the Sun makes it possible to change the seasons of the year. The planet would "tumble" in space if it did not have a strict orientation. There would be no question 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 during 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 about 24 hours. This period is called a day.

The speed of rotation determines the speed of the change 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 / s. Closer to the poles, this figure decreases. At the thirtieth latitude, the linear speed will already be 1445 km / h (400 m / s).

Due to axial rotation, the planet has a slightly compressed shape from the poles. Also, this movement "forces" moving objects (including air and water flows) to deviate from the original direction (Coriolis force). Another important consequence of this rotation is the ebbs and flows.

the change of night and day

A spherical object with the only light source at a certain moment is only half illuminated. In relation to our planet in one part of it at this moment there will be a day. The unlit part will be hidden from the Sun - there is night. Axial rotation makes it possible to change 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 cycle 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 overheat or cool below the optimum.

The rotation of the Earth around the Sun and its axis with a relatively constant speed is of decisive importance for the animal world. Without the constancy of the orbit, the planet would not have stayed in the zone of optimal heating. 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

Mankind 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 to a certain extent is influenced by the ellipse of the orbit and other planets of the system.

Another feature is the change in the length of the day. The axial rotation of the Earth is uneven. There are several main reasons. Seasonal fluctuations associated with the dynamics of the atmosphere and the distribution of precipitation are important. In addition, the tidal wave, directed against the motion of the planet, constantly slows it down. This figure is negligible (for 40 thousand years for 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 affect human life processes and natural phenomena in hydrometeorology and other fields.

Sun's annual path

The expression "the path of the Sun among the stars" will seem strange to someone. You can't see the stars during the day. Therefore, it is not easy to notice that the Sun slowly, by about 1˚ per day, moves among the stars from right to left. But you can see how the appearance of the starry sky changes during the year. All this is a consequence of the revolution of the Earth around the Sun.

The path of the visible annual movement of the Sun against the background of stars is called the ecliptic (from the Greek "eclipsis" - "eclipse"), and the period of revolution along the ecliptic is called the stellar year. It is equal to 265 days 6 hours 9 minutes 10 seconds, or 365.2564 mean solar days.

The ecliptic and the celestial equator intersect at an angle of 23˚26 "at the points of the spring and autumn equinoxes. At the first of these points, the Sun usually happens on March 21, when it passes from the southern hemisphere of the sky to the northern one. In the second, on September 23, when they pass from their northern hemisphere In the farthest point of the ecliptic to the north, the Sun is June 22 (summer solstice), and to the south - December 22 (winter solstice).In a leap year, these dates are shifted by one day.

Of the four points on the ecliptic, the main point is the vernal equinox. It is from her that one of the celestial coordinates is measured - right ascension. It also serves to count sidereal time and the tropical year - the time interval between two successive passages of the center of the Sun through the vernal equinox. The tropical year determines the change of seasons on our planet.

Since the vernal equinox slowly moves among the stars due to the precession of the earth's axis, the duration of the tropical year is less than the duration of the sidereal one. It is 365.2422 mean solar days.

About 2 thousand years ago, when Hipparchus compiled his star catalog (the first to have come down to us in its entirety), the vernal equinox was in the constellation Aries. By our time, it has moved almost 30˚, into the constellation of Pisces, and the autumn equinox point has moved from the constellation of Libra to the constellation of Virgo. But according to tradition, the points of the equinoxes are designated by the former signs of the former "equinoctial" constellations - Aries and Libra. The same happened with the solstice points: the summer in the constellation Taurus is marked by the sign of Cancer, and the winter in the constellation of Sagittarius is marked by the sign of Capricorn.

And finally, the last thing is connected with the apparent annual movement of the Sun. Half of the ecliptic from the spring equinox to the autumn equinox (from March 21 to September 23) the Sun takes 186 days. The second half, from the autumn equinox to the spring equinox, takes 179 days (180 in a leap year). But after all, the halves of the ecliptic are equal: each is 180˚. Therefore, the Sun moves along the ecliptic unevenly. This unevenness is explained by a change in the speed of the Earth's movement in an elliptical orbit around the Sun.

The uneven movement of the Sun along the ecliptic leads to different lengths of the seasons. For residents of the northern hemisphere, for example, spring and summer are six days longer than autumn and winter. The Earth on June 2-4 is located from the Sun 5 million kilometers longer than on January 2-3, and moves in its orbit more slowly in accordance with Kepler's second law. In summer, the Earth receives less heat from the Sun, but summer in the Northern Hemisphere is longer than winter. Therefore, the Northern Hemisphere is warmer than the Southern Hemisphere.

SOLAR ECLIPSES

At the time of the lunar new moon, a solar eclipse can occur - after all, it is on the new moon that the Moon passes between the Sun and the Earth. Astronomers know in advance when and where a solar eclipse will be observed, and report this in astronomical calendars.

The earth got a single satellite, but what a satellite! The Moon is 400 times smaller than the Sun and just 400 times closer to the Earth, so in the sky the Sun and the Moon appear to be disks of the same size. So during a total solar eclipse, the Moon completely obscures the bright surface of the Sun, while leaving the entire solar atmosphere exposed.

Exactly at the appointed hour and minute, through the dark glass, one can see how something black crawls from the right edge onto the bright disk of the Sun, as a black hole appears on it. It gradually grows, until finally the solar circle takes the form of a narrow sickle. At the same time, daylight quickly weakens. Here the Sun completely hides behind a dark curtain, the last daylight ray goes out, and the darkness, which seems the deeper, the more suddenly it is, spreads around, plunging man and all nature into silent surprise.

The English astronomer Francis Bailey tells about the eclipse of the Sun on July 8, 1842 in the city of Pavia (Italy): “When a total eclipse came and the sunlight instantly went out, some kind of bright radiance suddenly appeared around the dark body of the Moon, similar to a crown or a halo around the head saint. No account of past eclipses had anything like that written, and I did not expect to see the splendor that was now before my eyes. The width of the crown, measured from the circumference of the disk of the Moon, was equal to about half the lunar diameter. It seemed to be made up of bright rays. Its light was denser near the very edge of the moon, and as it moved away, the rays of the corona became weaker and thinner. The weakening of the light proceeded quite smoothly with increasing distance. The corona appeared in the form of beams of direct weak rays; their outer ends diverged like a fan, the rays were of unequal length.The crown was not reddish, not pearly, it was completely white. Its rays shimmered or shimmered like a azov flame. No matter how brilliant this phenomenon was, no matter how delighted it might be from the audience, there was definitely something sinister in this strange, marvelous spectacle, and I fully understand how shocked and frightened people could be at a time when these phenomena happened completely unexpectedly.

The most surprising detail of the whole picture was the appearance of three large ledges (prominences), which rose above the edge of the Moon, but obviously formed part of the crown. They looked like mountains of enormous height, like the snowy peaks of the Alps when they were illuminated by the red rays of the setting sun. Their red color faded into lilac or purple; perhaps the shade of peach blossoms would be best suited here. The light of the protrusions, in contrast to the rest of the crown, was completely calm, the "mountains" did not sparkle or shimmer. All three protrusions, somewhat different in size, were visible until the last moment of the total phase of the eclipse. But as soon as the first ray of the Sun broke through, the prominences, together with the corona, disappeared without a trace, and the bright light of day was immediately restored. "This phenomenon, so subtly and colorfully described by Bailey, lasted a little more than two minutes.

Remember the Turgenev boys in the Bezhinsky Meadow? Pavlusha talked about how the Sun could not be seen, about a man with a jug on his head, who was mistaken for the Antichrist Trishka. So it was a story about the same eclipse on July 8, 1842!

But there was no eclipse in Russia more than that, about which the "Word of Igor's Campaign" and ancient chronicles tell. In the spring of 1185, Prince Igor Svyatoslavich of Novgorod-Seversky and his brother Vsevolod, filled with the spirit of war, went to the Polovtsians to gain glory for themselves, and booty for the squad. On May 1, in the late afternoon, as soon as the regiments of the "Dazhd-God's grandchildren" (descendants of the Sun) entered a foreign land, it got dark earlier than expected, the birds fell silent, the horses neighed and did not go, the shadows of the horsemen were unclear and strange, the steppe breathed cold. Igor looked around and saw that "the sun standing like a month" was seeing them off. And Igor said to his boyars and his retinue: "Do you see? What does this radiance mean??" They looked, and saw, and lowered their heads. And the men said: "Our prince! This radiance does not bode well for us!" Igor answered: "Brothers and retinue! The mystery of God is unknown to anyone. And what God will give us - for our good or for grief - we will see." On the tenth day of May, Igor's squad perished in the Polovtsian steppe, and the wounded prince was taken prisoner.

Earth performs not only diurnal rotational motion around the axis (in more detail:), but also has translational movement along its orbit around the sun, together with other planets, which, however, we do not notice. Earth around the sun. It seems to us that the Earth is in a stationary state, and the Sun revolves around it. To most visually imagine, imagine that your ship has dropped anchor and set up on a roadstead near some port city. You lowered the boat and went to the mouth of a small river. The weather is clear and calm. The boat is rushing along the water surface, and it seems that the banks of the river are quickly running towards you, and the boat is standing still. This is the same motionless people used to consider the Earth, observing the apparent movement of the Sun through the zodiac constellations.

Total in solar system known nine large planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The planets do not have their own light, and if sometimes we observe them in the form of very bright stars, this is because they reflect the light of the Sun falling on them.
The planets move across the sky between the stars, which is why they were called planets, that is, "wandering luminaries."

Periods of rotation of the planets around the sun

Speeds and rotation periods of the planets around the sun vary depending on their distance from the Sun. Planets closer to the Sun rotate at a faster rate and complete their path around it in much shorter periods of time than planets farther from the Sun. For example, Mercury- the planet closest to the Sun - makes its way around the Sun in just 88 days. Pluto, which is the farthest distance from the Sun compared to all other planets known to us, is in 249 earth years.

The paths the planets take around the sun

The paths the planets take around the sun, they are called orbits. The orbits of the planets are ellipses, or elongated circles. This was first proved by a brilliant mathematician and astronomer Johannes Kepler. The degree of elongation of the planetary orbits is different and relatively small. The orbits of Mercury and Pluto are the most elongated. As for the earth's orbit, we can say that it almost does not differ from the circle. An ellipse is easy to draw. Take a short thread and tie its ends together. We put this thread on two pins stuck in a sheet of paper lying tightly on the table, one from the other at a distance slightly less than half of the entire thread. We stretch the thread with a pencil and, keeping it in this position, draw it over a sheet of paper lying on the table. Get an ellipse. The points where the pins are stuck are called tricks. The sun is in one of the foci of the ellipses of the orbits of the Earth and all other planets in the solar system. The foci of the planetary orbits are very close to the centers of the ellipses, which lie just in the middle between the foci.

Distance of the Earth from the Sun

The average Earth's distance from the Sun is about 150 million kilometers. This distance is almost 3750 times the circumference of the earth's equator. To cover the distance from the Earth to the Sun, a train moving at a speed of 50 kilometers per hour must go without stopping for about 350 years. Even on a plane flying at a speed of about 350 kilometers per hour, it would take us 50 years to reach the Sun. The Earth makes a complete revolution around the Sun in a year, more precisely in 365 ¼ days. At this time, our planet covers a distance of about 900 million kilometers in world space. For more than 20 thousand years, a pedestrian must walk non-stop, passing 5 kilometers every hour to cover this distance. An airplane flying at a speed of 350 kilometers per hour would take about 300 years to make a non-stop flight at a distance equal to the annual path of our Earth. Every second, the Earth moves in its orbit by almost 30 kilometers.. At one o'clock she passes the path is about 108 thousand kilometers. Imagine now how long the annual path of the Earth is and with what tremendous speed it rushes through the boundless expanses of the world. We, regular earthly passengers, do not feel any tremors or any other inconveniences in our journey through the Universe on this “ship”. We are not afraid of the abyss that surrounds us - we have firmly settled on our Earth. If we could create such a flying projectile, the flight speed of which would be equal to the speed of the Earth along its orbit, or at least even 11-12 kilometers per second, then this projectile would leave the Earth during its first flight and, having overcome its force of gravity, forever would hide from our eyes in the boundless space of the world. If we had such a gun, the shells of which would have a flight speed of about 9 kilometers per second, then these shells would turn into eternal satellites of our planet, they would forever circle the Earth and could not fly far into outer space, nor fall to the ground.

Earth's path in orbit

The Earth does not move at the same speed in its orbit around the Sun. The closer it is to the Sun, the greater its speed, and, conversely, as it moves away from the Sun, its speed decreases. AT aphelion point(the point in the earth's orbit that is farthest from the sun), the speed of the earth's movement is the smallest, and at the point of perihelion(the point in the earth's orbit that is closest to the Sun) is the largest.

Our planet is constantly in motion:

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

Earth's motion around its own axis

Rotation of the Earth around its axis(Fig. 1). An imaginary line is taken for the earth's axis, around which it rotates. This axis is deviated by 23 ° 27 "from the perpendicular to the plane of the ecliptic. The earth's axis intersects with the earth's surface at two points - the poles - the 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 makes a complete rotation around its axis in one day.

Rice. 1. Rotation of the Earth around its axis

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

sidereal day is the amount of time it takes the earth to rotate on its axis with respect to the stars. They are equal to 23 hours 56 minutes 4 seconds.

solar day is the amount of time it takes for the earth to rotate on its axis with respect 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 surface of the Earth moves 15° from its original position. But at the same time, the speed of movement is inversely proportional to the geographical latitude: at the equator it is 464 m / s, and at a latitude of 65 ° - only 195 m / s.

The rotation of the Earth around its axis in 1851 was proved by J. Foucault in his experiment. 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 turned out to be on new divisions. This can only happen if the surface of the Earth under the pendulum rotates. The position of the swing plane of the pendulum at the equator does not change, because the plane coincides with the meridian. The axial rotation of the Earth has important geographic consequences.

When the Earth rotates, a centrifugal force is created, 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 turning 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 the 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 deviates to the right, and in the Southern - 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 geographic 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 - east. 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, in the Southern - the left).

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 animate and inanimate nature. The daily rhythm is closely related to light and temperature conditions. The daily course of temperature, day and night breezes, etc. are well known. Daily rhythms also occur in wildlife - 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 proceeds in a daily rhythm.

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

Since 1884, a zone time account 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. Neighboring time zones differ by one hour. The boundaries of the belts are drawn taking into account political, administrative and economic boundaries.

The zero belt is Greenwich (by the name of the Greenwich Observatory near London), which runs on both sides of the zero meridian. The time of the zero, or initial, meridian is considered World Time.

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

For a more rational use of daylight in summer in 1930, our country introduced maternity time, ahead of the zone by one hour. To do this, the hands of the clock 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, between April and October, the time has been moved forward one hour. This so-called summer time. It is introduced to save energy. In summer, Moscow is two hours ahead of standard time.

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 considered 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, around and helios- Sun) - the closest point of the orbit to the Sun - on January 3, the distance is 147 million km. It is winter in the Northern Hemisphere at this time. The farthest distance from the Sun in aphelion(from Greek. aro- away from and helios- Sun) - the greatest distance from the Sun - July 5. It is equal to 152 million km. At this time, it is summer in the Northern Hemisphere.

Rice. 4. 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 height of the Sun and the position of its sunrise and sunset change, the duration of the bright 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 a change 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 during the year. This is how the seasons change, which is typical for all planets that have an inclination of the axis of rotation 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, and the summer half-year - 186 days.

As a result of the movement of the Earth around the Sun and the inclination of the earth's axis to the plane of its orbit by 66.5 °, not only the change of seasons is observed on our planet, 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 according to the seasons in the Northern Hemisphere).

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

Equinox- the moment 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 inclination of the Earth's axis of rotation around the Sun on the equinoxes of March 20-21 and September 22-23 is neutral with respect to the Sun, and the parts of the planet facing it are uniformly 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 of passage by the center of the Sun of the points of the ecliptic, the most distant from the equator (solstice points). There are summer and winter solstices.

On the day of the summer solstice on June 21-22, the Earth takes 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, whose latitude is 23 ° 27 "All day and night, not only the polar regions are illuminated, but also the space beyond them up to latitude 66 ° 33" (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 ") turns out to be illuminated. Beyond it, on this day, the earth's surface is not illuminated.

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

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

At two parallels of the Earth on the days of the solstice, the Sun at noon is directly above the head of the observer, that is, at the zenith. Such parallels are called tropics. On the Tropic of the North (23° N), the Sun is at its zenith on June 22, on the Tropic of the South (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 expressed.

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 from the Arctic Circle near the pole, the longer the polar day. At the latitude of the Arctic Circle (66.5°) it lasts only one day, and at the Pole it lasts 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 dawn 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 belts. The hot belt lies between the Northern and Southern tropics (the Tropic of Cancer and the 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 zones of illumination. The seasons of the year are already expressed here: the farther from the tropics, the shorter and cooler the summer, the longer and colder the winter. The polar belts in the Northern and Southern Hemispheres are limited by the Arctic Circles. Here, the height of the Sun above the horizon during the year is low, 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, there are not only the change of seasons and the associated uneven illumination of the earth's surface across latitudes, but also a significant part of the processes in the geographical envelope: seasonal weather changes, the regime of rivers and lakes, the rhythm in the life of plants and animals, types and terms 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, the change in the 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 duration of the Julian year is longer than the astronomical one by 11 minutes 14 seconds, by the 16th century. an “error” of 10 days accumulated - the day of the vernal equinox did not come on March 21, but on March 11. This mistake was corrected in 1582 by a decree of Pope Gregory XIII. The count of days was moved forward by 10 days, and the day after October 4 was prescribed to be considered Friday, but not October 5, but October 15. The spring equinox was again returned to March 21, and the calendar became known as the Gregorian. It was introduced in Russia in 1918. However, it also has a number of drawbacks: uneven length of months (28, 29, 30, 31 days), inequality of quarters (90, 91, 92 days), inconsistency of numbers of months by days of the week.