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?

(The change of night and day)

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 heat(up to 100 degrees Celsius) and all the water would have evaporated; on the other side, on the contrary, frosts would have raged and the water would have been under a thick layer of ice. Both the first and second conditions would be unacceptable for the development of life and the existence of the human species.

Why do the seasons change?

(Change of seasons on Earth)

Due to the fact that the axis is inclined relative to the earth's surface at a certain angle, its sections receive different time different amounts of heat and light, which causes the change of seasons. According to the astronomical parameters necessary to determine the time of year, 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 at this time receives a lot of heat and light, long live summer! 6 months pass and the Earth moves to the opposite point of its orbit and the Northern Hemisphere 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.

Basic movements of the Earth in space

© Vladimir Kalanov,
website"Knowledge is power".

Our planet rotates around its own axis from west to east, that is, counterclockwise (when viewed from the North Pole). An axis is a conditional straight line crossing the globe in the region of the North and South Poles, that is, the poles have a fixed position and “do not participate” in rotational motion, while all other location points on the earth’s surface rotate, with a linear rotation speed of surface of the globe depends on the position relative to the equator - the closer to the equator, the higher the linear speed of rotation (let us explain that the angular speed of rotation of any ball is the same at its various points and is measured in rad/sec, we are discussing the speed of movement of an object located on surface of the Earth and the higher it is, the further the object is removed from the axis of rotation).

For example, at the mid-latitudes of Italy the rotation speed is approximately 1200 km/h, at the equator it is maximum and amounts to 1670 km/h, while at the poles it is zero. 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 the 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, as was previously thought.

Day. What are sidereal and solar days?

A day is the length 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 for the Earth’s rotation, in which the Sun is taken as the starting point. Another concept is “sidereal day” (from lat. sidus - Genitive sideris- star, celestial body) - implies another starting point - a “fixed” star, the distance to which tends to infinity, and therefore we assume that its rays are mutually parallel. The length of the two types of days differs from each other. A sidereal day is 23 hours 56 minutes 4 seconds, while the duration of a solar day is slightly longer and is equal to 24 hours. The difference is due to the fact that the Earth, rotating around its own axis, also performs an orbital rotation around the Sun. It's easier to figure this out with the help of a drawing.

Solar and sidereal days. Explanation.

Let's consider two positions (see figure) that the Earth occupies when moving along its orbit around the Sun, “ A" - the observer's place on the earth's surface. 1 - the position that the Earth occupies (at the beginning of the countdown of the day) either from the Sun or from any star, which we define as the reference point. 2 - the position of our planet after completing a revolution around its own axis relative to this star: the light of this star, and it is located on great distance, will reach us parallel to the direction 1 . When the Earth takes its position 2 , we can talk about “sidereal days”, because The Earth has made a full revolution around its axis relative to the distant star, but not yet relative to the Sun. The direction of observing the Sun has changed somewhat due to the rotation of the Earth. In order for the Earth to make a full revolution around its own axis relative to the Sun (“solar day”), you need to wait until it “turns” about 1° more (equivalent to the daily movement of the Earth at an angle - it travels 360° in 365 days), this It will take just about four minutes.

In principle, the length of a solar day (although it is taken to be 24 hours) is not a constant value. This is due to the fact that the Earth's orbital movement actually 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, a concept such as "average solar day", precisely their duration is twenty-four hours.

In addition, it has now been reliably established that the period of rotation of the Earth increases under the influence of the changing tides caused by the Moon. The slowdown is approximately 0.002 s per century. The accumulation of such, at first glance, imperceptible deviations means, however, that from the beginning of our era to the present day, the total slowdown is already about 3.5 hours.

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 the Moon 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 149.6 million kilometers. In astronomy, the unit used to measure distances within solar system ; they call her "astronomical unit"

(a.e.). 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", and is maintained throughout the entire orbit.

The change of seasons is a consequence of the Earth's revolution around the Sun. The reason for seasonal changes is the inclination of the Earth's rotation axis to the plane of its orbit. Moving along an elliptical orbit, the Earth in January is at the point closest to the Sun (perihelion), and in July at the point farthest from it - aphelion. The reason for the change of seasons is the inclination of the orbit, as a result of which the Earth tilts towards the Sun with one hemisphere and then the other and, accordingly, receives a different amount of sunlight. In summer, the Sun reaches the highest point of the ecliptic. This means that the Sun makes its longest movement over the horizon during the day, and the length of the day is maximum. In winter, on the contrary, the Sun is low above the horizon, the sun's rays fall on the Earth not directly, but obliquely. The length of the day is short.

Depending on the time of year, different parts of the planet are exposed to the sun's rays. The rays are perpendicular to the tropics during the solstice.

Seasons in the Northern Hemisphere

Annual movement of the Earth

Determining the year, the basic calendar unit of time, is not as simple as it seems at first glance, and depends on the chosen reference system.

The time interval during which our planet completes its orbit around the Sun is called a year. However, the length of the year varies depending on whether the starting point is taken to measure it infinitely distant star or Sun.

In the first case we mean “sidereal year” (“sidereal year”) . It is equal 365 days 6 hours 9 minutes and 10 seconds and represents the time required for the Earth to completely revolve around the Sun.

But if we measure the time required for the Sun to return to the same point in the celestial coordinate system, for example, at the vernal equinox, then we get the duration "solar year" 365 days 5 hours 48 minutes 46 seconds. The difference between stellar and solar year occurs due to the precession of the equinoxes; every year the equinoxes (and, accordingly, the sun stations) come “earlier” by approximately 20 minutes. compared to the previous year. Thus, the Earth moves around its orbit a little faster than the Sun, in its apparent movement through the stars, returns to the vernal equinox.

Considering that the duration of the seasons is in close connection with the Sun, when compiling calendars, it is taken as a basis "solar year" .

Also in astronomy, instead of the usual astronomical time, determined by the period of rotation of the Earth relative to the stars, a new uniformly flowing time, not related to the rotation of the Earth and called ephemeris time, was introduced.

Read more about ephemeris time in the section: .

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The Earth, rotating from west to east (when viewed from the North Pole), makes a complete revolution around its axis in 24 hours. The angular velocity of rotation of all points on the Earth is the same (15° per hour). The linear speed of rotation of the points depends on the distance they must travel during the daily rotation of the Earth. Only the exit points of the imaginary axis remain motionless on the Earth's surface - the points of the geographic poles (North and South). WITH highest speed(464 m/sec) points rotate on the equator line, on the line great circle, formed by the intersection of the Earth with a plane perpendicular to the axis of rotation. If you mentally cross the Earth next to planes parallel to the equator, lines will appear on the earth's surface in the direction of west - east, called parallels. The length of the parallels decreases from the equator to the poles, and the linear speed of rotation of the parallels decreases accordingly. The linear speed of rotation of all points on one parallel is the same.
When planes passing through the Earth's rotation axis cross the Earth, lines appear on its surface in a north-south direction, meridians(meridianus, lat. - midday). The linear speed of rotation of all points on one meridian is not the same: from the equator to the poles it decreases.
Convincing proof of the Earth's rotation around its axis is the experiment with a swinging pendulum (Foucault's experiment).
According to the laws of mechanics, every swinging body strives to maintain the plane of swing. A freely suspended swinging pendulum does not change the plane of swing, and at the same time, if a circle with divisions is placed on the surface of the Earth like a pendulum, it turns out that in relation to this circle (i.e. in relation to the surface of the Earth) the position of the plane of swing of the pendulum changes. This can only happen due to the fact that the surface of the Earth under the pendulum rotates. At the pole, the apparent rotation of the pendulum's swing plane will be 15° per hour; at the equator, the position of the pendulum's swing plane does not change, since it always coincides with the meridian; at intermediate latitudes, the apparent rotation of the swing plane is 15° sin φ per hour (φ is the geographic latitude of the observation site).
Deflecting effect of the Earth's rotation (Coriolis force)- one of the most important consequences of the Earth's rotation. We usually orient the direction of movement of bodies in relation to the sides of the horizon (north, south, east, west), i.e. in relation to the lines of meridians and parallels, forgetting that these lines, due to the rotation of the Earth, continuously change their orientation in world space . A body in motion, according to the law of inertia, strives to maintain the direction and speed of its movement relative to world space. Let, for example, let a rocket be launched from point A (in the northern hemisphere) towards the North Pole (Fig. 13). At the moment of launch, the direction of its movement (AB) coincides with the direction of the meridian. But already in next moment Point A, as a result of the rotation of the Earth, will move to the right, to point B. The direction of the meridian in space will change, the meridian will deviate to the left. The rocket, on the contrary, will maintain the direction of movement, but to the observer watching its movement, it seems that under the influence of some force it has deviated to the right. It is not difficult to understand that this force is fictitious, since the rocket only appears to be deflected due to a change in the direction of the meridian along which the observer orients the direction of its movement. If a body moves in the northern hemisphere from north to south, the meridian changes its direction, moving to the left, and the observer sees the moving body deviating, just as when moving from south to north, to the right.

The deviation will be greatest at the poles, since there the meridian changes its direction in world space by 360° per day. The deviation decreases from the poles and the equator, and at the equator, where the meridians are parallel to each other and their direction in space does not change, the deviation is 0.
In the southern hemisphere, the deflecting effect of the Earth's rotation is manifested in the deflection of moving bodies to the left.
Bodies moving in any direction deviate from the direction of movement to the right in the northern hemisphere and to the left in the southern.
The deflecting force of the Earth's rotation (Coriolis force), acting on a unit of mass (1 g), moving at a speed of V m/sec, is expressed by the formula F=2ω*v*sin φ, where φ is the angular velocity of the Earth's rotation, φ is latitude. The Coriolis force does not depend on the direction of motion of the body and does not affect its speed.
The deflecting effect of the Earth's rotation has a constant effect on the direction of movement of all bodies on Earth, in particular it significantly affects the direction of air and sea currents.
Change of day and night on Earth. Sun rays They always illuminate only the half of the Earth facing the Sun. The rotation of the Earth around its axis causes the rapid movement of solar illumination across the earth's surface from east to west, i.e., the change of day and night.

If the Earth's axis were perpendicular to the orbital plane, the luminous plane (the plane dividing the Earth into illuminated and unilluminated halves) would divide all latitudes into two equal parts and at all latitudes day and night would always be equal. When the axis is inclined to the plane of the earth's orbit, day and night can be equal at all latitudes only at the moment when the earth's axis lies in the light-separating plane and when the light-separating line (the line formed by the intersection of the earth's surface with the light-separating plane) passes through the geographic poles. When the earth's axis is inclined with its northern end towards the Sun (Fig. 14, a), the light-separating plane, crossing the earth's axis in the center of the Earth, divides the Earth into two halves so that most of the northern hemisphere is illuminated, and the smaller part is in the shadow, and vice versa , most of the southern hemisphere is in shadow. If the Earth's axis is tilted towards the Sun with its southern end (Fig. 14, b), the southern hemisphere is illuminated more than the northern. Since the light dividing line in both cases does not pass through the geographic poles and divides all latitudes, except 0°, into two unequal parts - illuminated and unilluminated, day and night at all latitudes except the equator are not equal. In the hemisphere that is inclined towards the Sun, the day is longer than the night, in the opposite hemisphere, on the contrary, it is night longer than a day. At those latitudes that are not intersected by the light dividing line and for some time find themselves completely on the illuminated or unlit side of the Earth, during the corresponding period (up to six months at the poles) the change of day and night does not occur. If the change of day and night is determined by the rotation of the Earth about its axis, and their inequality is determined by the inclination of the axis to the Earth’s orbit, then the constant change in the duration of day and night at all latitudes except the equator is the result of the constant position of the Earth’s axis in space as the Earth revolves around the Sun.

The Earth rotates around an axis from west to east, that is, counterclockwise when looking at the Earth from the North Star (North Pole). In this case, the angular velocity of rotation, i.e. the angle through which any point on the Earth’s surface rotates, is the same and amounts to 15° per hour. Linear speed depends on latitude: at the equator it is highest - 464 m/s, and the geographic poles are stationary.

The main physical proof of the Earth's rotation around its axis is the experiment with Foucault's swinging pendulum. After the French physicist J. Foucault carried out his famous experiment in the Paris Pantheon in 1851, the rotation of the Earth around its axis became an immutable truth. Physical evidence of the Earth’s axial rotation is also provided by measurements of the arc of the 1° meridian, which is 110.6 km at the equator and 111.7 km at the poles (Fig. 15). These measurements prove the compression of the Earth at the poles, and this is characteristic only of rotating bodies. And finally, the third evidence is the deviation of falling bodies from the plumb line at all latitudes except the poles (Fig. 16). The reason for this deviation is due to their inertia maintaining a higher linear velocity of the point A(at height) compared to point IN(near the earth's surface). When falling, objects are deflected to the east on the Earth because it rotates from west to east. The magnitude of the deviation is maximum at the equator. At the poles, bodies fall vertically, without deviating from the direction of the earth's axis.

The geographic significance of the Earth's axial rotation is extremely large. First of all, it affects the figure of the Earth. The compression of the Earth at the poles is the result of its axial rotation. Previously, when the Earth rotated at a higher angular velocity, the polar compression was greater. The lengthening of the day and, as a consequence, a decrease in the equatorial radius and an increase in the polar one is accompanied by tectonic deformations of the earth's crust (faults, folds) and a restructuring of the Earth's macrorelief.

An important consequence of the Earth’s axial rotation is the deflection of bodies moving in a horizontal plane (winds, rivers, sea currents, etc.). from their original direction: in the northern hemisphere – right, in the south - left(this is one of the forces of inertia, called the Coriolis acceleration in honor of the French scientist who first explained this phenomenon). According to the law of inertia, every moving body strives to maintain unchanged the direction and speed of its movement in world space (Fig. 17). Deflection is the result of the body participating in both translational and rotational movements simultaneously. At the equator, where the meridians are parallel to each other, their direction in world space does not change during rotation and the deviation is zero. Toward the poles, the deviation increases and becomes greatest at the poles, since there each meridian changes its direction in space by 360° per day. The Coriolis force is calculated by the formula F = m x 2ω x υ x sin φ, where F – Coriolis force, T– mass of a moving body, ω – angular velocity, υ – speed of a moving body, φ – geographical latitude. The manifestation of the Coriolis force in natural processes is very diverse. It is because of it that vortices of different scales arise in the atmosphere, including cyclones and anticyclones, winds and sea currents deviate from the gradient direction, influencing the climate and through it the natural zonality and regionality; The asymmetry of large river valleys is associated with it: in the northern hemisphere, many rivers (Dnieper, Volga, etc.) for this reason have steep right banks, left banks are flat, and in the southern hemisphere it’s the other way around.

Associated with the rotation of the Earth is a natural unit of time measurement - day and it happens the change of night and day. There are sidereal and sunny days. Sidereal day– the time interval between two successive upper culminations of a star through the meridian of the observation point. During a sidereal day, the Earth makes a complete rotation around its axis. They are equal to 23 hours 56 minutes 4 seconds. Sidereal days are used for astronomical observations. True solar days– the period of time between two successive upper culminations of the center of the Sun through the meridian of the observation point. The length of the true solar day varies throughout the year, primarily due to the uneven movement of the Earth along its elliptical orbit. Therefore, they are also inconvenient for measuring time. For practical purposes they use average sunny days. Mean solar time is measured by the so-called mean Sun - an imaginary point that moves evenly along the ecliptic and makes a full revolution per year, like the true Sun. The average solar day is 24 hours long. They are longer than sidereal days, since the Earth rotates around its axis in the same direction in which it moves in its orbit around the Sun with an angular velocity of about 1° per day. Because of this, the Sun moves against the background of the stars, and the Earth still needs to “turn” by about 1° for the Sun to “come” to the same meridian. Thus, during a solar day, the Earth rotates approximately 361°. To convert true solar time to mean solar time, a correction is introduced - the so-called equation of time. Its maximum positive value+ 14 minutes on February 11, the greatest negative –16 minutes on November 3. The beginning of the average solar day is taken to be the moment of the lowest culmination of the average Sun - midnight. This kind of time counting is called civil time.

In everyday life, it is also inconvenient to use mean solar time, since it is different for each meridian, local time. For example, on two adjacent meridians drawn with an interval of 1°, local time differs by 4 minutes. The presence of different local times at different points lying on different meridians led to many inconveniences. Therefore, at the International Astronomical Congress in 1884, zone time was adopted. To do this, the entire surface of the globe was divided into 24 time zones, 15° each. Behind standard time The local time of the middle meridian of each zone is accepted. To convert local time to standard time and back, there is a formula T n – m = N – λ °, Where T P – standard time, m - local time, N– number of hours equal to the belt number, λ ° – longitude expressed in hourly units. The zero (also known as the 24th) belt is the one through the middle of which the zero (Greenwich) meridian passes. His time is taken as universal time. Knowing universal time, it is easy to calculate standard time using the formula T n = T 0 + N, Where T 0 - universal time. The belts are counted to the east. In two neighboring zones, the standard time differs by exactly 1 hour. For convenience, the boundaries of time zones on land are drawn not strictly along meridians, but along natural boundaries (rivers, mountains) or state and administrative boundaries.

d. This “shift” operates throughout Russia, except for the Kaliningrad region, where the time actually corresponds to the second time zone. Rice. 17. Deviation of bodies moving along the meridian in the northern hemisphere - to the right, in the southern hemisphere - to the left In a number of countries, time is moved forward one hour only in the summer. In Russia, since 1981, for the period from April to October, summer time by moving the time another hour ahead compared to maternity leave. Thus, in summer time in Moscow actually corresponds to local time on the meridian 60°E. d. The time according to which residents of Moscow and the second time zone in which it is located live is called

Moscow. According to Moscow time, our country schedules trains and planes, and marks the time on telegrams. In the middle of the twelfth zone, approximately along the 180° meridian, in 1884 a

international date line. This is 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 example, on New Year’s Day at 0:00 a.m. to the west of this line it is already January 1 of the new year, and to the east it is only December 31 of the old year. When crossing the border of dates from west to east, one day is returned in the count of calendar days, and from east to west one day is skipped in the count of dates. in living and inanimate nature. The circadian rhythm is associated with light and temperature conditions. The daily variation of temperature, day and night breezes, etc. are well known. The daily rhythm of living nature is very clearly manifested. It is known that photosynthesis is possible only during the day, in the presence of sunlight, and that many plants open their flowers at different hours. Animals can be divided into nocturnal and diurnal according to the time of their activity: most of them are awake during the day, but many (owls, bats, moths) are awake in the darkness of the night. Human life also flows in a circadian rhythm.

Rice. 18. Twilight and white nights

The period of smooth transition from daylight to night darkness and back is called at dusk. IN they are based on an optical phenomenon observed in the atmosphere before sunrise and after sunset, when the sun is still (or already) below the horizon, but illuminates the sky from which the light is reflected. The duration of twilight depends on the declination of the Sun (the angular distance of the Sun from the plane of the celestial equator) and the geographic latitude of the observation site. At the equator, twilight is short and increases with latitude. There are three periods of twilight. Civil twilight are observed when the center of the Sun plunges below the horizon shallowly (at an angle of up to 6°) and for a short time. This is actually White Nights, when the evening dawn meets the morning dawn. In summer they are observed at latitudes of 60° and more. For example, in St. Petersburg (latitude 59°56" N) they last from June 11 to July 2, in Arkhangelsk (64°33" N) - from May 13 to July 30. Navigational twilight observed when the center of the solar disk plunges 6–12° below the horizon. In this case, the horizon line is visible, and from the ship you can determine the angle of the stars above it. And finally, astronomical twilight are observed when the center of the solar disk plunges below the horizon by 12–18°. At the same time, the dawn in the sky still prevents astronomical observations of faint luminaries (Fig. 18).

The rotation of the Earth gives two fixed points - geographic poles(the points of intersection of the imaginary axis of rotation of the Earth with the earth's surface) - and thereby allows you to construct a coordinate grid of parallels and meridians. Equator(lat. aequator - leveler) - the line of intersection of the globe with a plane passing through the center of the Earth perpendicular to its axis of rotation. Parallels(Greek parallelos – running side by side) – lines of intersection of the earth’s ellipsoid with planes parallel to the equatorial plane. Meridians(lat. meridlanus - midday) - the line of intersection of the earth's ellipsoid with planes passing through both of its poles. The length of the 1st meridian is on average 111.1 km.