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

Another of the most important consequences of axial rotation is the formation of a 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 inertial 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 belt. 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 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: unequal duration of months (28, 29, 30, 31 days), inequality of quarters (90, 91, 92 days), inconsistency of numbers of months by days of the week.

The Earth has 3 movements:

1. Orbital (from west to east counterclockwise)

2. Rotation around its own axis (from west to east counterclockwise)

3. Movement of the Earth-Moon system

Consequences of the first movement.

1. Aphelion (July 5) - the farthest distance from the Earth to the Sun, Perihelion (January 3) - the closest distance.

The first geographical consequence is the phenomenon of precession (equinox). Precession is a slow cone-shaped movement of the earth's axis around the perpendicular plane of the orbit with the apex at the center of the earth. This is due to the action of the Moon and the Sun.

June 22 is the summer solstice for the northern hemisphere or the winter solstice for the southern. On this day, the Sun is at its zenith over the northern tropic. The Earth's axis is tilted to the Sun by the north pole, so the northern hemisphere receives more heat than the southern one, in the northern hemisphere the day is longer than the night, the northern subpolar region is illuminated around the clock. In the southern hemisphere, the opposite is true.

September 23 - autumn for the northern hemisphere and spring for the southern equinox. Both hemispheres are illuminated equally, on the whole planet day is equal to night, at noon the sun is at its zenith above the equator.

December 22 is the winter (northern hemisphere) and summer (southern hemisphere) solstice. The sun is at its zenith over the southern tropic.

The second geographical consequence is the change of seasons and the inequality of day and night.

There are five lighting zones (thermal zones). Their boundaries are the lines of the tropics and polar circles.

Hot belt. Lies between the tropics. At the equator, day is always equal to night; at other latitudes of this belt, their duration varies little.

temperate zones. Located between the tropics and the polar circles. During the day, there is a change of day and night, and their duration depends on the position of the Sun.

Cold belts. They are located north of the northern and south of the southern circles. They are distinguished by the presence of polar days and nights.

Thermal belts are the basis of climatic zoning and natural zoning in general.

Consequences of rotation around its axis.

1. Change of day and night. The units of time are the day (stellar and solar).

2. The earth is flattened at the poles.

3. Coriolis force. Deviation of bodies moving horizontally to the right in the northern hemisphere and to the left in the southern hemisphere.

4. Geographical poles are taken as permanent fixed points.

The consequence of the movement of the Earth-Moon system: the Moon always faces the Earth with one side, since the Moon rotates around its axis with the same period and in the same direction in which it revolves around the Earth.

Movement of the Earth around the Sun and its geographical consequence (annual)

The Earth moves around the Sun in an elliptical orbit at a speed of 30 km/s. The length of this orbit is 930 million km, and the Earth makes a complete revolution in 365 days 6 hours 9 minutes and 9 seconds (stellar year). The Earth's axis is inclined to the plane of the orbit by 66.5? and this slope is constantly maintained. As a result, the sun's rays fall on the earth's surface unevenly. The heat from the sun also comes in unevenly. This leads to unequal duration of day and night at all latitudes (except the equator) and to the change of seasons on our planet.

The path of the Sun between these four points (equinoxes and solstices) is divided into sectors of 90? every. The passage of the Sun through each of the sectors causes a change of seasons on Earth (autumn, winter, spring, summer). When the Earth turns its Northern Hemisphere towards the Sun, in all countries located north of the equator, summer sets in and the day lengthens, and in countries south of the equator, winter sets in and the day shortens.

The ellipticity of the orbit of the annual motion of the Earth leads to changes in the speed of its movement around the Sun. Being at perihelion (closest to the Sun), the Earth has a maximum speed of movement, so autumn and winter in the Northern Hemisphere are shorter than other seasons, in the Southern Hemisphere - summer is shorter and winter is longer.

Geographical consequences of the Earth's movement - phenomena caused by different types of Earth's movement and affecting the shape of the Earth, natural processes and human life: the change of day and night, the change of seasons, the deviation of the movement of bodies under the influence of Coriolis acceleration, tides, tides, etc.

1) White nights - bright nights, when evening twilight merges with morning ones, and night darkness does not occur. White nights are observed in both hemispheres at latitudes above 60 degrees. In St. Petersburg, white nights last from June 11 to July 2, in Arkhangelsk from May 13 to July 30. Beyond the Arctic Circle, white nights precede the polar day and are observed for some time after its end.

2) Change of seasons;

3) The law of river channel migration - in physical geography - the law according to which rivers, as a result of the deflecting action of the Earth's rotation around its axis, tend to shift their channel in the northern hemisphere to the right, and in the southern hemisphere - to the left. Consequence: In the rivers of the Northern Hemisphere, the right bank is usually steep, and the left bank is gentle.

4) Polar night - the period when the Sun in high latitudes does not rise above the horizon for many days; a phenomenon opposite to the polar day; observed simultaneously with it at the corresponding latitudes of the other hemisphere.

5) Polar day - the period when the Sun in high latitudes does not fall below the horizon for many days. The duration of the polar day is longer, the farther to the pole from the Arctic Circle. In the polar circles, the Sun does not set only on the day of the solstice, at 68 degrees. latitude, the polar day lasts about 40 days, at the North Pole - 189 days.

6) Equinox - the moment when the Sun, during its apparent annual movement along the ecliptic, crosses the celestial equator: the sun's rays touch both poles, and the earth's axis is perpendicular to the rays. The spring equinox occurs on March 21-22, autumn - September 22-23. At the equinox, the Northern and Southern hemispheres are equally illuminated, on the whole Earth (excluding the regions of the poles) the day is equal to the night, at one pole the Sun rises, at the other it sets.

7) Time counting systems - methods of counting time intervals by comparing them with the accepted basic units, which are used as various natural or artificial periodic processes: the revolution of the Earth around the Sun, the rotation of the Earth, the swing of a pendulum, the oscillation of a quartz plate, etc. The establishment and control of timekeeping systems is carried out by national and international time services.

8) 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 (June 21-22), the longest day in the Northern Hemisphere is reached. In the Southern Hemisphere at this time the shortest day.

On the day of the winter solstice (December 21-22), the picture is reversed: the shortest day in the Northern Hemisphere, the longest in the Southern.

9) Coriolis acceleration - acceleration relative to the surface of the Earth, experienced by any moving body due to the fact that the rotating Earth is not an inertial coordinate system.

Coriolis acceleration is associated only with a moving frame of reference.

The Coriolis acceleration in the Northern Hemisphere is directed to the right in relation to the direction of motion, in the Southern Hemisphere - to the left, and is equal to zero at the equator, and has a maximum value at the poles; its value does not depend on the direction of motion.

The material gives an idea of ​​what the axial rotation of the planet is. Reveals the mystery of the rising and setting of the sun and indicates the factors that influence the shape of the earth as a result of its rotation.

Axial rotation of the earth and its consequences

Thanks to astronomical observations, a fact has been established that proves that the Earth simultaneously takes an active part in several types of movement. If we consider our planet as part of the solar system, then it makes revolutions around the center of the Milky Way. And if we consider the planet as a unit of the Galaxy, then it is already a participant in the movement at the galactic level.

Rice. 1. Axial rotation of the earth.

The main type of motion that has been studied by scientists since ancient times is the rotation of the Earth around its own axis.

The axial rotation of the Earth is called its measured rotation around the represented axis. All objects that are on the surface of the planet also rotate with it. The rotation of the planet is made in the opposite direction relative to the usual clockwise movement. Thanks to this, the sunrise can be celebrated in the east, and the sunset in the west. The Earth's axis has an angle of inclination equal to 661/2° relative to the orbital plane.

The axis has clear reference points in the space of space: its northern tip is always facing the Polar Star.

The axial rotation of the Earth gives an idea of ​​the apparent movement of celestial bodies without the use of specialized equipment.

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Rice. 2. The movement of the stars and the moon across the sky.

The rotation of the earth causes the cycle of day and night. A day is the period of absolute rotation of the planet around its axis. The length of the day depends on the speed of the planet's rotation.

Due to the rotation of the planet, all bodies moving on its surface deviate from the original direction in the Northern Hemisphere to the right in the course of their movement, and in the Southern Hemisphere - to the left. In rivers, such a force to a greater extent pins water to one of the banks. At the water arteries of the Northern Hemisphere, the right bank often remains steep, and in the Southern - the left.

Rice. 3. River banks.

Effect of axial rotation on the shape of the earth

Planet Earth is a perfect sphere. But due to the fact that it is slightly compressed at the poles, the distance from its center to the poles is 21 kilometers less than the distance from the center of the Earth to the equator. Therefore, the meridians are 72 kilometers shorter than the equator.

Axial rotation causes:

• diurnal changes;
• the flow of light and heat to the surface;
• the ability to observe the obvious movement of celestial bodies;
• differences in time in different parts of the earth.

To understand how axial rotation affects the shape of the earth, one must take into account the operation of generally accepted laws of physics. As already noted, the planet has a "flattening" at the poles due to the action of centrifugal force and gravity on it.

The planet rotates in the same way as it moves around the sun. Such quantities as the shape, parameters and movement of the Earth play an important role in the development of all geographical phenomena and processes.

Today it is reliably known that the Earth is actually gradually slowing down its rotation. Due to the strength of the tides that connect our planet with the moon, every century the day becomes longer by 1.5-2 milliseconds. In almost one and a half million years there will be one hour more in a day. People should not be afraid of a complete stop of the Earth. Civilization simply will not live up to this point. In about 5 billion years, the Sun will increase in size and swallow our planet.

What have we learned?

From the geography material for grade 5, we learned what the rotation of the planet around its axis affects. What forces act on the shape of the earth. What determines the division of the earth's day into day and night. What causes the earth to be heated by the sun's rays. Which can lead to an extra hour in the day. What cosmic body could theoretically swallow the earth.

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There are two main types of Earth's motion: in orbit around the Sun and around its own axis of rotation.

Orbit (from lat. orbita- track, road) of the Earth - an ellipse close to a circle, in one of the focuses of which the Sun is located. The distance from the Earth to the Sun varies throughout the year from 147 million km at perihelion (January 3) to 152 million km at aphelion (July 5).

The length of the orbit is more than 930 million km. The Earth moves in orbit with an average speed of about 30 km/s and travels all the way in a year - in 365 days. 6 h 9 min 9 s. The axis of rotation of the Earth is inclined to the plane of the orbit at an angle of 66.5°; is directed to the North Star (in the current astronomical epoch) and moves in space parallel to itself during the year. These circumstances lead to the most important geographical consequences - the change of seasons, the inequality of day and night, the natural daily measurement of time.

used in astronomical observations sidereal day - the time interval between two successive highest positions of a star above the horizon on the meridian of the observation point. During a sidereal day, the Earth makes a complete rotation around its axis in 23 hours 56 minutes and 4 seconds. For practical purposes, apply sunny days - the time interval between two successive passages of the center of the Sun through the meridian of the observation point (24 hours).

Adopted in everyday life lap time count. To this end, the entire surface of the globe was divided into 24 time zones of 15 ° each. Standard time is the local time of the middle meridian of each zone. We agreed that the zero and at the same time the 24th belt will be the one in the middle of which the Greenwich meridian runs. It was also accepted that in the middle of the 12th belt, approximately along the 180 ° meridian, date line. This is a conditional border, but both sides of which the time value coincides, and the calendar dates differ by one day.

If the axis of rotation of the Earth were perpendicular to the plane of the orbit, then the light dividing line on its surface (Terminator) would pass through both poles and divide all the parallels in half. In this case, the day would always be equal to the night, the sun's rays would fall on the equator at a right angle and there would be no change of seasons. The real picture of the illumination of the planet is shown in Fig. 3.7.

Rice. 3.7.

and winter solstice:

1 - illuminated half (day); 2 - unlit half (night)

The inclination of the Earth's axis of rotation to the plane of the orbit and the preservation of the orientation of the axis in space cause a different angle of incidence of the sun's rays in time. Accordingly, there are differences in the flow of heat to the earth's surface, as well as unequal duration of day and night during the year at all latitudes, except for the equator. The division by the terminator of all parallels in half and the equality of the length of day and night is observed only on days equinoxes- March 21 (astronomical spring) and September 23 (astronomical autumn).

On June 22, the earth's axis with its northern end is turned towards the Sun. On this day - summer solstice- the sun's rays at noon fall vertically on the parallel 23.5 ° N.L. - so-called northern tropic. All parallels north of the equator up to 66.5°N. most of the day is illuminated and at these latitudes the day is longer than the night. North of 66.5°N on the day of the summer solstice, the territory is completely illuminated by the Sun - there polar day.

Parallel 66.5°N is the boundary from which the polar day begins - this is Arctic Circle. On the day of the summer solstice on all parallels south of the equator to 66.5 ° S. day is shorter than night. South of 66.5°S the area is not lit at all - there polar night. Parallel 66.5° S - south polar circle. June 22 is considered the beginning of astronomical summer in the northern hemisphere and astronomical winter in the southern hemisphere.

December 22 - in winter solstice - the earth's axis with its southern end is facing the sun. The sun's rays at noon fall vertically on the parallel 23.5 ° S. latitude. - southern tropic. On all parallels south of the equator up to 66.5°S. the day is longer than the night. Starting from the southern polar circle, the polar day is established. On this day, on all parallels north of the equator up to 66.5 ° N.L. day is shorter than night.

As a result of the tilt of the axis of rotation and the annual movement of the Earth, five lighting belts, which form the climatic and natural zonality.

hot belt lies between the tropics (northern and southern) and occupies about 40% of the earth's surface.

temperate zones(two) are located between the tropics and the polar circles. The sun in them is never at its zenith. During the day, there is a change of day and night. In summer we see "white nights" near the polar circles (from 60 to 66.5°). The total area of ​​temperate zones is 52% of the earth's surface.

cold belts(two) are located north of the northern and south of the southern polar circles. They are distinguished by the presence of polar days and nights, the duration of which increases from one day at the polar circles to six months at the poles. Their total area is 8% of the earth's surface.

associated with the rotation of the earth Coriolis effect, which is important in physical and geographical processes. From the course of physics, we know that the movement of liquids and gases over a certain surface is mainly due to horizontal changes in pressure. Initially, we will consider the theory of such motion in the air without taking into account the rotation of the Earth. It is obvious that the elementary volume of air, which is subjected to pressure from three sides R, ace one side ( X) - pressure R+ D R(i.e. somewhat larger), will have to move in the direction of the axis x. Therefore, one would expect that the winds would be directed from an area of ​​high pressure to areas of low pressure, since this direction would coincide with the direction of the force acting on the air.

What do the observations show? Meteorological stations around the world continuously measure various weather characteristics - atmospheric pressure, air temperature, wind direction and strength, precipitation, evaporation, etc. This data is sent to national weather bureaus where it is collected and analyzed to provide a synoptic (simultaneous) view of the weather. Then "weather maps" are built, on which the observed distribution of atmospheric pressure at sea level is depicted by thick lines connecting points with equal pressure values ​​(isobars). In addition, indications of wind directions and speeds are noted. On the synoptic map (IN) areas of high air pressure are indicated, and the letter (77) - areas of low pressure. Air whirlwinds, called cyclones, are associated with areas of low air pressure, and anticyclones are associated with high pressure.

Based on the considered "pure" theory, one would expect that the wind in our experiment would blow through the isobars: from high pressure to low. However, an analysis of the observed wind directions shows that this is not the case. Instead of moving through the isobars, the wind blows along them: in cyclones - counterclockwise, and in anticyclones - clockwise in the northern hemisphere, and in the southern - vice versa. Thus, the wind is approximately perpendicular to the direction of the force due to horizontal pressure changes.

At first glance, the wind data seem strange and contrary to theory. But the theory is not wrong, it is only imperfect, since in our reasoning we did not take into account the rotation of the Earth. If the Earth did not rotate around its axis, then the wind would indeed blow from areas of high air pressure to areas of its low pressure.

The rotation of the Earth plays a very important role in the formation of geospheric processes. Under its influence, a force arises that deflects moving bodies to the right in the northern hemisphere and to the left in the southern. The first scientific explanation of the deflecting force of the Earth's rotation was given by the French physicist GG Coriolis in 1835. The Coriolis force balances the pressure gradient. An approximate balance between the Coriolis force and the pressure gradient exists not only in the atmosphere, but also in the ocean.

Coriolis acceleration is always directed at right angles to the velocity vector V(cm/s) and reaches its maximum values ​​near the poles. Its value decreases in proportion to the sine of latitude cp to zero at the equator: Coriolis acceleration= 1.5 10 4 x x V? sin f (cm / s 2).

The Coriolis acceleration acts like an incomplete barrier between the pole and the equator. As a result, the movement of water towards the pole is partially delayed, and to transfer the same amount of heat as in the absence of a barrier, a greater temperature difference is required. Rapid circulation occurs on both sides of the barrier, but through the barrier the exchange of water, and hence heat, will be weakened. A similar thermal barrier due to the Coriolis force is also observed in the atmosphere. In the ocean, the situation is complicated by the geographical distribution of land and sea.

An example of the influence of the Earth's rotation on circulation in the World Ocean is the strong western boundary currents in the northern hemisphere - these are the Kuroshio in the Pacific Ocean and the Gulf Stream in the Atlantic. It is known that the western boundary currents are better developed in the northern hemisphere than their counterparts in the southern. The reasons for this have not yet been elucidated. Deviating from the Asian and North American coasts to the right almost at an angle of 45°, the Kuroshio and Gulf Stream flows cross the ocean from west to east in the region of the fortieth parallel. Together with a horizontal change in water density, they lead to the formation of the North Pacific and North Atlantic currents, as well as to an increase in the temperature difference between equatorial and polar waters.

The movements of the Earth affect the formation of tides in the oceans. The connection of tides with the phases of the moon has long been noted. But for the first time, I. Newton managed to correctly explain this phenomenon in his published "Principles" (1687). Further development of the theory of tides was carried out by Laplace. He considered the tides as large waves with a period of 0.5 to 1 day. Tidal waves are nothing but fluctuations of the surface of the World Ocean relative to its average level under the influence of the attraction of the Earth by the Magnifier and the Sun. Moreover, the tide-forming force of the Moon, due to its proximity, is 2.17 times greater than the tide-forming force of the Sun. During a lunar day, which is 50 minutes longer than a solar day, there are two high tides and two low tides on Earth. The maximum tidal wave height of 18 m is observed in the Bay of Fundy between Brunswick and Nova Scotia (Canada).

Tidal fluctuations caused by the gravitational effects of the Moon and the Sun on the rotating Earth form the main semidiurnal and diurnal lunar tides with periods of about 12 hours 25 minutes and 24 hours 50 minutes and the main semidiurnal and diurnal solar tides with periods of half a day and a day. The interaction of these forces is complex due to differences in the position of the Sun and Moon relative to each other and the influence of the Earth's rotation. However, the main property of tidal oscillations is the formation reverse currents: at high tide, the mass of water rushes to the shore, and at low tide - from the coast. At the same time, the high tide is shorter in time than the low tide. Accordingly, the speed of the tidal current is higher than the speed of the ebb current.

It is known that, depending on the combination of the forces of lunar and solar attraction, the tide during the lunar month (28 days) twice reaches its maximum and minimum values. Also, the tides change with the seasons. During the periods of the full moon and new moon, the tides are greatest (the so-called syzygy tides). The minimum tides are called quadrature, since they are observed during quadratures, i.e. the first and third quarters of the phases of the moon. The greatest magnitude of the tides in syzygy is explained by the fact that during the new moon and full moon the Moon and the Sun are approximately on the same straight line with the Earth and the vectors of the tide-forming forces add up, and in quadratures they act at right angles to each other, as a result of which during these lunar phases the tides become the least. Large differences in the amplitude of the tides in different parts of the coast are determined mainly by the shape of the ocean basins.

Due to the importance of tides for shipping, many luminaries of world science have been studying them. After Newton and Laplace, the problem of tides was studied by the greatest mathematicians of the 18th century, but the physicist Lord Kelvin made a practical contribution to the prediction of tides. In 1870, he proposed the idea that the height of the tide at any location could be predicted by representing its various components as a function of the known movements of the Sun and Moon. For the convenience of calculations, Kelvin designed the world's first analog machine. He built tables of tide heights for various ports of the world. The true picture of the distribution of tide heights near the coast of the World Ocean is shown in Fig. 3.8.

Rice. 3.8.

Finally, consider inertial vibrations (air, water). These include motions on the level surface in the absence of external forces, in particular, baric gradient and friction, under the conditions of a rotating Earth, i.e. in the presence of the deflecting force of the Earth's rotation. The deflecting force during inertial movements is balanced by the centrifugal force. Inertial motions occur along a curvilinear trajectory (clockwise in the northern hemisphere, counterclockwise in the southern hemisphere). The trajectory of inertial motions is circular (the so-called circle of inertia).

As an example, we will demonstrate the formation of inertial circulation in the southern part of the Baltic Sea based on the results of expeditionary research. The program of our experiments provided for many days of observation of a pair of special buoys launched from the ship and observed with the help of the ship's locator. The buoys were parallelepipeds assembled on the basis of an openwork structure with sides of 1.5 1.0 m, equipped with masts with metal reflectors at the top and plumb lines at the bottom. Continuous registration of the position of the buoys in space after their simultaneous release from the ship made it possible to obtain the trajectories of motion. In particular, in fig. 3.9

one of such trajectories, recorded by instrumental observations in the sea, is shown. You can notice periodic movements in closed elliptical orbits after 14.8 hours.

The obtained value of the period of oscillations in the indicated region is associated precisely with inertial waves.

Rice. 3.9.

The trajectories of movement in the sea of ​​two discrete indicators (1,2) are built according to the experimental data in the Gulf of Riga. The numbers at the points indicate astronomical time; x, y- Cartesian coordinate axes; axis at directed north.

The considered main movements of the Earth - in orbit around the Sun and axial rotation - form the change of seasons, climatic zoning, the inequality of day and night, and also create a daily rhythm in living and inanimate nature.