8. Axial rotation of the Earth and its evidence. Axial rotation of the Earth and its geographical consequences.
The earth rotates around its axis from west to east, that is, counterclockwise, if you look at the earth from the North Star (from the North Pole). In this case, the angular velocity of rotation, i.e., the angle by which any point on the surface of the Earth rotates, is the same and amounts to 15 ° per hour. Linear speed depends on latitude: at the equator it is the highest - 464 m / s, and the geographical poles are fixed.
The main physical proof of the rotation of the Earth 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 indisputable truth.
Physical evidence of the Earth's axial rotation is also measured by the 1° meridian arc, which is 110.6 km at the equator and 111.7 km at the poles. These measurements prove the compression of the Earth at the poles, and it is characteristic only of rotating bodies. And finally, the third proof is the deviation of falling bodies from the plumb line at all latitudes, except for the poles. The reason for this deviation is due to the preservation by inertia of a greater linear velocity of point A (at a height) compared to point B (near the earth's surface). Falling objects are deflected on the Earth to the east 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 geographical significance of the axial rotation of the Earth is exceptionally great. 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 contraction was more significant. Lengthening of the day and, as a result, a decrease in the equatorial radius and an increase in the polar one is accompanied by tectonic deformations earth's crust(faults, folds) and the restructuring of the Earth's macrorelief.
An important consequence of the axial rotation of the Earth is the deviation of bodies moving in a horizontal plane (winds, rivers, sea currents, etc.) from their original direction: in the northern hemisphere - to the right, in the southern hemisphere - to the 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, each moving body strives to keep the direction and speed of its movement in the world space unchanged.
Deviation is the result of the fact that the body participates simultaneously in both translational and rotational movements. 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. Towards 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*2w*v*sinj, where F is the Coriolis force, m is the mass of the moving body, w is the angular velocity, v is the speed of the moving body, j is the geographic latitude. The manifestation of the Coriolis force in natural processes is very diverse. It is because of it that vortices of various 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 (Dnepr, Volga, etc.) for this reason, the right banks are steep, the left ones are gentle, and vice versa in the southern hemisphere.
With the rotation of the Earth, a natural unit of time is associated - a day, and there is a change of day and night. Days are stellar and sunny. A sidereal day is the time interval between two consecutive upper culminations of a star through the meridian of the observation point. During a sidereal day, the Earth makes a complete revolution around its axis. They are equal to 23 hours 56 minutes 4 seconds. Sidereal days are used in astronomical observations. A true solar day is the time interval between two successive upper culminations of the center of the Sun through the meridian of the observation point. The length of a true solar day varies throughout the year primarily due to uneven movement Earth in an elliptical orbit. Hence, they are also inconvenient for measuring time. For practical purposes, the average solar day is used. Mean solar time is measured by the so-called mean Sun - an imaginary point that moves uniformly along the ecliptic and makes a complete revolution per year, like the true Sun. The average solar day is 24 hours. They are longer than stellar ones, since the Earth rotates around its axis in the same direction in which it orbits 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 around” by about 1 ° so that the Sun “comes” to the same meridian. Thus, in 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 is +14 min on February 11, the largest negative value is -16 min on November 3. The beginning of the average solar day is taken as the moment of the lower climax of the average Sun - midnight. This account of time is called civil time.
| " |
The rotation of the Earth around its axis is manifested in many phenomena on its surface. For example, the trade winds (constant winds in the tropical regions of both hemispheres, blowing towards the equator), due to the rotation of the Earth from west to east, blow from the northeast in the northern hemisphere and from the southeast in the southern hemisphere; in the northern hemisphere, the right banks of rivers are washed away, in the southern - the left; when a cyclone moves from south to north, its path deviates to the east, and so on.
a) b)
Rice. 12 : Foucault pendulum. BUT is the swing plane of the pendulum.
But the most obvious consequence of the rotation of the Earth is the experiment with a physical pendulum, first staged by the physicist Foucault in 1851.
Foucault's experience is based on the property of a free pendulum to keep the direction of the plane of its oscillations unchanged in space, if no force acts on it, except for gravity. Let the Foucault pendulum be suspended at the north pole of the Earth and oscillate at some point in the plane of a certain meridian l(fig.12, a). After some time, to an observer connected with the earth's surface and not noticing its rotation, it will seem that the plane of the pendulum's oscillations is continuously shifting in the direction from east to west, “behind the Sun”, i.e. clockwise (Fig. 12, 6 ). But since the swing plane of the pendulum cannot arbitrarily change its direction, we have to admit that in reality the Earth turns under it in the direction from west to east. In one sidereal day, the plane of oscillation of the pendulum will make a complete revolution relative to the Earth's surface with an angular velocity w= 15° per sidereal hour. On the south pole The pendulum of the earth will also make one revolution in 24 sidereal hours, but counterclockwise.
Fig 13.
If the pendulum is suspended on the earth's equator and the plane of its swing is oriented in the plane of the equator, i.e. at a right angle to the meridian l(Fig. 12), then the observer will not notice the displacement of the plane of his oscillations relative to terrestrial objects, i.e. it will appear stationary and remain perpendicular to the meridian. The result will not change if the pendulum at the equator oscillates in any other plane. It is usually said that at the equator the period of rotation of the plane of oscillation of the Foucault pendulum is infinitely large.
If the Foucault pendulum is hung at latitude j, then its oscillations will occur in a plane vertical for a given place on the Earth.
Due to the rotation of the Earth, it will seem to the observer that the plane of oscillation of the pendulum rotates around the vertical of this place. The angular velocity of this rotation w j is equal to the projection of the vector of the angular velocity of the Earth's rotation w onto the vertical at the given location O(Fig. 13), i.e.
w j --= w sin j= 15°sin j.
Thus, the angle of apparent rotation of the plane of oscillation of the pendulum relative to the surface of the Earth is proportional to the sine geographical latitude.
Foucault staged his experience by hanging a pendulum under the dome of the Pantheon in Paris. The length of the pendulum was 67 m, lentil weight - 28 kg. In 1931, in Leningrad, in the building of St. Isaac's Cathedral, a pendulum with a length of 93 m and weighing 54 kg. The oscillation amplitude of this pendulum is 5 m, the period is about 20 seconds. The tip of his lentil, with each subsequent return to one of the extreme positions, is shifted to the side by 6 mm. Thus, in 1-2 minutes you can make sure that the Earth really rotates around its axis.
Rice. fourteen
The second consequence of the Earth's rotation (but less obvious) is the deflection of falling bodies to the east. This experience is based on the fact that the farther a point is from the axis of rotation of the Earth, the greater its linear speed with which it moves from west to east due to the rotation of the Earth. Therefore, the top of the high tower AT moves to the east with a greater linear speed than its base O(Fig. 14). The movement of a body freely falling from the top of the tower will occur under the action of the Earth's gravity with the initial speed of the top of the tower. Consequently, before falling to the Earth, the body will move along an ellipse, and although the speed of its movement gradually increases, it will fall to the Earth's surface not at the base of the tower, but will somewhat overtake it, i.e. deviate from the base in the direction of the rotation of the Earth, to the east.
AT theoretical mechanics to calculate the magnitude of the deviation of the body to the east X the formula is obtained
where h- body fall height in meters, j- geographical latitude of the place of experience, and X expressed in millimeters.
The phenomena of daily rhythm and biorhythms are associated with axial movement. The daily rhythm is associated with light and temperature conditions. Biorhythms are an important process in the development and existence of life. Without them, photosynthesis, the vital activity of diurnal and nocturnal animals and plants and, of course, the life of the person himself (owl people, lark people) are impossible.
Currently, the rotation of the Earth is directly observed from space.
Earth (lat. Terra) is the third planet from the Sun in the solar system, the largest in diameter, mass and density among the planets terrestrial group.
The Earth interacts (is attracted by gravitational forces) with other objects in space, including the Sun and Moon. The Earth revolves around the Sun and makes a complete revolution around it in about 365.26 days. This period of time is a sidereal year, which is equal to 365.26 solar days. The Earth's axis of rotation is tilted 23.4° relative to its orbital plane, which causes seasonal changes on the planet's surface with a period of one tropical year (365.24 solar days).
One of the proofs of the Earth's orbital rotation is the change of seasons. Correct understanding of observable celestial phenomena and the place of the Earth in solar system evolved over the centuries. Nicolaus Copernicus finally broke the idea of the immobility of the Earth. Copernicus showed that it was the rotation of the Earth around the Sun that could explain the apparent loop-like motions of the planets. The center of the planetary system is the Sun.
The axis of rotation of the Earth is deviated from the axis of the orbit (i.e., a straight line perpendicular to the plane of the orbit) by an angle equal to approximately 23.5 °. Without this tilt, there would be no change of seasons. The regular change of seasons is a consequence of the movement of the Earth around the Sun and the inclination of the Earth's axis of rotation to the plane of the orbit. In the northern hemisphere of the Earth, summer comes, when the north pole of the Earth is illuminated by the Sun, and the south pole of the planet is located in its shadow. At the same time, winter is coming in the southern hemisphere. When it's spring in the northern hemisphere, it's autumn in the southern hemisphere. When it's autumn in the northern hemisphere, it's spring in the southern hemisphere. The seasons in the southern and northern hemispheres are always opposite. Around March 21 and September 23 around the world, day and night last 12 hours. These days are called the spring and autumn equinoxes. In summer, the duration of daylight hours is longer than in winter, therefore, the northern hemisphere of the Earth during spring and summer from March 21 to September 23 receives much more heat than in autumn and winter from September 23 to March 21.
As you know, the Earth revolves in its orbit around the Sun. For us, people on the surface of the Earth, such an annual movement of the Earth around the Sun is noticeable in the form of an annual movement of the Sun against the background of stars. As we already know, the path of the Sun among the stars is a great circle of the celestial sphere and is called the ecliptic. This means that the ecliptic is a celestial reflection of the Earth's orbit, so the plane of the Earth's orbit is also called the plane of the ecliptic. The axis of rotation of the Earth is not perpendicular to the plane of the ecliptic, but deviates from the perpendicular by an angle. Due to this, the seasons change on Earth (see Fig. 15). Accordingly, the plane of the earth's equator is inclined at the same angle to the plane of the ecliptic. The line of intersection of the plane of the earth's equator and the plane of the ecliptic retains (if precession is not taken into account) an unchanged position in space. One end points to the vernal equinox, the other to the autumn equinox. These points are fixed relative to the stars (up to precessional motion!) and together with them participate in the daily rotation.
Rice. fifteen.
Near March 21 and September 23, the Earth is located relative to the Sun in such a way that the boundary of light and shadow on the Earth's surface passes through the poles. And since each point on the surface of the Earth makes a daily movement around the earth's axis, then exactly half of the day it will be on the illuminated part the globe, and the second half - on the shaded one. Thus, on these dates, day equals night, and they are named accordingly. days spring and autumn equinoxes. The Earth at this time is on the line of intersection of the planes of the equator and the ecliptic, i.e. at the spring and autumn equinoxes, respectively.
We single out two more special points in the Earth's orbit, which are called solstices, and the dates on which the Earth passes through these points are called solstices.
At the point of the summer solstice, at which the Earth is near June 22 (the day of the summer solstice), the north pole of the Earth is directed towards the Sun, and for most of the day any point in the northern hemisphere is illuminated by the Sun, i.e. This date is the longest day of the year.
At the point of the winter solstice, at which the Earth is near December 22 (the day of the winter solstice), the north pole of the Earth is directed away from the Sun, and for most of the day any point of the northern hemisphere is in the shade, i.e. on this date, the night is the longest of the year, and the day is the shortest.
Because of calendar year in duration does not coincide with the period of revolution of the Earth around the Sun, the days of equinoxes and solstices in different years may fall on different days (-+ one day from the above dates). However, in the future, when solving problems, we will neglect this and assume that the days of equinoxes and solstices always fall on the dates indicated above.
Let's pass from the real motion of the Earth in space to visible movement Sun for an observer at latitude. During the year, the center of the Sun moves in a large circle of the celestial sphere, along the ecliptic, counterclockwise. Since the plane of the ecliptic in space is fixed relative to the stars, the ecliptic, together with the stars, will participate in the daily rotation of the celestial sphere. Unlike the celestial equator and the celestial meridian, the ecliptic will change its position relative to the horizon during the day.
How do the coordinates of the Sun change during the year? Right Ascension changes from 0 to 24 h, and the declination changes from - to +. This can best be seen on a celestial map of the equatorial zone (Fig. 16).
Rice. 16.
For four days in a year, we know the coordinates of the Sun exactly. The table below provides this information.
Table 2. Data on the Sun during the equinoxes and solstices
|
t. sunrise |
t. |
h max |
||
|
0 h 00 m |
||||
|
23 o 26" |
6 h 00 m |
north-east |
||
|
12 h 00 m |
||||
|
23 o 26" |
18 h 00 m |
The table also shows the noon (at the time of the upper culmination) height of the Sun for these dates. In order to calculate the height of the Sun at the moments of culminations on any other day of the year, we need to know that day.
The earth rotates west to east counterclockwise, making a complete rotation per day. The average angular velocity of rotation, i.e. the angle by which the point is displaced by earth's surface, is the same for all latitudes and amounts to 15 ° in 1 hour. Linear speed, i.e. the path traveled by a point in a unit of time, depends on the latitude of the place. The geographic poles do not rotate, where the speed is zero. At the equator, the point travels the longest path and has the highest speed of 455 m / s. The speed on one meridian is different, on the same parallel it is the same.
The proof of the rotation of the Earth is the figure of the planet itself, the presence of compression of the earth's ellipsoid. Compression occurs with the participation of centrifugal force, which in turn develops on a rotating planet. Every point on Earth is affected gravity and centrifugal force. The resultant of these forces is directed towards the equator, because the Earth in the equatorial belt is convex, at the poles it has compression.
Geographic consequences of the Earth's axial rotation include the emergence of the Coriolis force, the daily rhythm in the geographic envelope.
Tidal protrusions formed in the body of the Earth (in the lithosphere, oceanosphere and atmosphere) by the attraction of the Moon and the Sun turn into a tidal wave that goes around the globe, moving towards its rotation, i.e. from east to west. The passage of a wave crest through a place creates a tide here, the passage of a depression creates an ebb. During a lunar day (24 hours 50 minutes) there are two high tides and two low tides.
The tides are of the greatest geographical importance: they lead to regularly alternating flooding and drainage of low-lying coasts, backwater in the lower reaches of the rivers and the emergence of tidal currents. The average height of the tide in open ocean about 20 cm, sea level fluctuations near the coast, depending on the tides, are somewhat larger, but usually do not exceed 2 m, although in some cases they reach 13 m (Penzhinskaya Bay) and even up to 18 m (Fandi Bay).
An important consequence of the axial rotation of the Earth is the apparent deviation of bodies moving in a horizontal direction from the direction of their movement. According to the law of inertia, any moving body tends to keep the direction (and speed) of its movement relative to the World space. If the motion is relative to a moving surface, such as the rotating Earth, it appears to an observer on Earth that the body has deflected. In reality, the body continues to move in a given direction.
The Coriolis force increases from the equator to the poles, it contributes to the formation of atmospheric vortices, affects the deviation of sea currents, thanks to it the right banks of rivers in the Northern Hemisphere are washed away, the left banks in the Southern Hemisphere.
In areas far from the equator, the most important for a well-established air movement is most often the Coriolis force. Consider an air particle in the northern hemisphere moving from an area of high pressure to an area of low pressure due to the force of a pressure gradient. Assume that the isobars are straight lines and there is no friction.
Fig.3.4
The Coriolis force will turn the air particle to the right, and the sum of the pressure gradient force (PGD) and the Coriolis force (SC) will increase the speed. As the speed of the particle increases, the Coriolis force, proportional to the speed and, will also increase, which means that its deflecting action will also increase. At the point where the particle begins to move perpendicular to the SHD, the SC and SHD act in opposite directions, and the resulting force will depend on which of them is greater. If this is an SHD, the acceleration will be directed to the left of the motion, the speed will increase and the Coriolis force will also increase, which will cause the particle to move in the opposite direction. If the Coriolis force turns out to be greater, it will cause the particle to deviate more to the right, its speed will decrease, which means that the Coriolis force will decrease, which will force the particle to return back. As a result, an equilibrium can be established if the SHD remains constant during the entire time while the particle moves perpendicular to it, and the SC is exactly equal to it in magnitude and opposite in direction. In this case, the particle does not experience acceleration, and the motion is called geostrophic. The corresponding wind blows parallel to the isobars so that in the northern hemisphere the high pressure region remains to its right. In the southern hemisphere, on the contrary, the area of high pressure remains to the left. These statements form the essence of what was formulated in the 19th century. Bays-Ballo's law, which states: if you face the wind in the northern hemisphere, then low pressure will be to your right, in the south - to your left.
The daily rotation of the Earth is uneven: in August it is faster, in March it is slower (the difference in the length of the day is about 0.0025 sec.). Its periodic changes are associated with seasonal changes in the circulation of the atmosphere, a shift in the centers of high and low atmospheric pressure; for example, in winter, the excess pressure of cold air masses on Eurasia is 5 10 12 tons, in summer all this mass returns to the ocean. Oscillations are spasmodic, irregular (as a result of which the length of the day can change up to 0.0034 sec.) are stimulated by the movement of masses inside the Earth. The approach of the masses to the axis of rotation or their removal from the axis entails, respectively, the acceleration or deceleration of the daily rotation. Pulsations in the speed of the Earth's rotation can be caused and climate change, entailing a redistribution of water masses on the surface, for example, the transition of a significant part of the hydrosphere into a solid phase.
Most interesting, however, is the secular variation of the rotation rate. The effect of deceleration of this speed by a tidal wave running towards the rotation of the Earth turns out to be stronger than the effect of an increase in speed from gravitational compression and compaction. internal parts planets. As a result, the duration of a day on Earth increases by 1 second every 40,000 years. (according to other data - by 0.64 s. for the same period).
These values should be kept in mind when making paleogeographic constructions. If we take the first value (1 s in 40,000 years), it is easy to calculate that 500 million years ago, i.e., at the turn of the Cambrian and Ordovician, the day was a little longer than 20 hours, and 1 billion years ago (in the Proterozoic ) --17 o'clock. In the latter case, the subtropical maxima of atmospheric pressure, which now lie at latitudes of ± 32 °, should have been located on parallels of ± 22 °, i.e., be a tropical maximum, with all the ensuing consequences for general atmospheric circulation on Earth. After 1 billion years, the duration of the day will increase to 31 hours (because there will be only 283 days in the year). In the end, due to tidal braking, the Earth will turn to the Moon all the time on one side, as it already happened with the Moon in relation to the Earth, and the Earth day will become equal to the lunar month.
Back in the II century BC. The Greek astronomer Hipparchus discovered that the vernal equinox slowly moves relative to the stars towards annual movement Sun. Due to the fact that the equinox occurs before the Sun makes a complete revolution along the ecliptic, the phenomenon is called the precession of the equinoxes or precession. The magnitude of this shift per year is called the constant precession and, according to modern data, is about 50".
The precessional movement of the earth's axis is mainly caused by the attraction of the moon and the sun. If the Earth were a sphere, then it would be attracted by the Moon and the Sun by forces applied to its center. But since the Earth is flattened towards the poles, then a force will act on the equatorial bulge, tending to rotate the Earth in such a way that its equatorial plane passes through the attracting body. This force creates a tilting moment. The Sun departs twice a year from the plane of the Earth's equator at an angle e ~ 23°26", and the removal of the Moon twice a month can reach 28°36". However, the relatively fast axial rotation of the Earth creates a gyroscopic effect, due to which the deviation occurs in a direction perpendicular to operating force. A similar effect is observed in a rotating gyroscope - under the action of an external force, its axis begins to describe a cone in space, the narrower the faster the rotation.
Fig.3. 5Scheme of formation of the overturning moment acting on the Earth from the side of the Sun and the Moon. The forces acting on the equatorial bulge (at points A and B) are decomposed into components parallel to the direction of the perturbing body from the center of the Earth O, and components perpendicular planes earth's equator (AA" and BB"). The latter act as overturning forces.
In relation to the Earth, the main external force is the attraction of the Sun, which causes the main part of the displacement of the earth's axis with a period of 26,000 years. Since the period of rotation of the nodes of the Moon's orbit is 18.6 years, the limits of the change in the angle of deviation of the Moon from the plane of the Earth's equator also change with the same period, which manifests itself in the form of nutations with the same period. The magnitude of precession and nutation could be calculated theoretically, but for this there is not enough data on the distribution of masses inside the Earth, and therefore it has to be determined from observations of the positions of stars in different epochs.
The "strength" of our planet depends on the angular velocity of rotation. The centrifugal force at the equator is 1/289 of the earth's gravity. With the acceleration of the Earth's rotation by 17 times, the centrifugal force would increase by 17 2 = 289 times, the bodies at the equator would lose their weight, and a part of the substance could be separated from the Earth. Obviously, the Earth is insured against such a fate with its 17-fold margin of safety, which, moreover, gradually increases due to a decrease in the rotation speed and, consequently, a weakening of the centrifugal force.
The change of day and night creates a daily rhythm in the geographical shell, it manifests itself in living and inanimate nature: in the daily course of all meteorological elements - temperature, humidity, pressure; the melting of mountain glaciers occurs during the day; photosynthesis occurs during the day, in the light, many plants open at different hours of the day. Man also lives by the clock; at certain hours, his working capacity drops, his body temperature and pressure rise.
The period of revolution of the Moon in orbit is about 28 days, during which time it returns to its original place. And what happens under our feet? Everyone knows about the tides of the sea. Water is attracted by the gravitational force of the Moon, and such a wave follows the surface of the seas and oceans after the Moon. But gravity acts separately on each atom and molecule, attracting them. It’s just that it’s more visible on the water because of its uniformity on a huge scale and fluidity. Every part of our body also experiences an ebb and flow of gravitational force. Liquid blood especially. And all the life cycles of the body are tied to the period of the moon's revolution. It is assumed that the moon specifically affects the state of the vegetative nervous system and for such important structures brain like cerebellum, hypothalamus, pineal gland. It is noted that during the full moon, the working capacity of a person and the excitability of his nervous system increase, irritability increases, and during the new moon, the opposite picture is observed (weakness, decreased activity, creative powers and abilities) and as a result of this, a connection can be traced between the mood of people and the change of lunar phases.
The particles of the solid Earth also experience the cyclic effect of the gravitational force. If flowing water is attracted to the moon by several meters, then solid earth is stretched towards the moon by half a meter and a few centimeters to the side.
At the north pole of the Earth, the Sun is a non-setting luminary for about half a year, and a non-rising luminary for about half a year. Around March 21, the Sun appears above the horizon here (rises) and, due to the daily rotation of the celestial sphere, describes curves close to a circle and almost parallel to the horizon, rising higher and higher every day. On the day of the summer solstice (around June 22), the Sun reaches its maximum height h max = + 23 ° 27 ". After that, the Sun begins to approach the horizon, its height gradually decreases and after the autumn equinox (after September 23) it disappears under the horizon The day, which lasted half a year, ends and a night begins, which also lasts half a year. The sun, continuing to describe curves, almost parallel to the horizon, but below it, sinks lower and lower, On the day of the winter solstice (about December 22) it will sink below the horizon to a height hmin \u003d - 23 ° 27 ", and then it will again begin to approach the horizon, its height will increase, and before the day of the vernal equinox, the Sun will again appear above the horizon. For an observer at the south pole of the Earth (j = - 90°), the daily motion of the Sun occurs in a similar way. Only here the Sun rises on September 23, and sets after March 21, and therefore, when it is night at the north pole of the Earth, it is day at the south, and vice versa.
The shape of the Earth depends on the size of the planet, the distribution of densities in it and on the speed of axial rotation. None of these factors can be called stable.
Due to the deep compression of the Earth, its radius is reduced by about 5 cm per century, which means that the volume of the Earth is also becoming smaller. However, this secular decrease is pulsatile because it is interrupted for a time by periods of Earth expansion caused by the enormous amount of heat released by the shrinking radius.
The processes described above are also reflected in the speed of the Earth's rotation: when the radius is shortened, this speed increases, and when the radius is lengthened, it slows down. Consequently, with a secular trend towards a decrease in the volume of the planet, the secular trend in the change in the speed of its rotation should go in the direction of accelerating this rotation. But since another (and, moreover, a very powerful) factor intervenes in the matter - tidal braking, in the end, the speed of the Earth's rotation systematically becomes less. And this means a weakening in the secular perspective of the polar compression of the Earth.
The earth rotates around an axis from west to east, i.e. counterclockwise, if you look at the Earth from the North Star (from North Pole). In this case, the angular velocity of rotation, i.e., the angle by which any point on the surface of the Earth rotates, is the same and amounts to 15 ° per hour. Linear speed depends on latitude: at the equator it is the highest - 464 m / s, and the geographical poles are fixed.
The main physical proof of the rotation of the Earth 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 indisputable truth. Physical evidence of the Earth's axial rotation is also the measurement of the 1° meridian arc, which is 110.6 km near the equator and 111.7 km near the poles (Fig. 15). These measurements prove the compression of the Earth at the poles, and it is characteristic only of rotating bodies. And finally, the third proof is the deviation of falling bodies from the plumb line at all latitudes, except for the poles (Fig. 16). The reason for this deviation is due to their retention by inertia of a greater linear velocity of the point BUT(at height) compared to point AT(near the earth's surface). Falling objects are deflected on the Earth to the east 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 geographical significance of the axial rotation of the Earth is exceptionally great. 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 contraction was more significant. The lengthening of the day and, as a result, 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 axial rotation of the Earth 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 southern to the left(this is one of the forces of inertia, named Coriolis acceleration in honor of the French scientist who first explained this phenomenon). According to the law of inertia, each moving body strives to keep the direction and speed of its movement in the world space unchanged (Fig. 17). Deviation is the result of the fact that the body participates simultaneously in both translational and rotational movements. 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. Towards 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 is the Coriolis force, t is the mass of the moving body, ω is the angular velocity, υ is the speed of the moving body, φ is the geographic latitude. The manifestation of the Coriolis force in natural processes is very diverse. It is because of it that vortices of various 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 (Dnepr, Volga, etc.) for this reason, the right banks are steep, the left ones are gentle, and vice versa in the southern hemisphere.
The rotation of the Earth is associated with a natural unit of time measurement - day and going on the change of night and day. Days are stellar and sunny. sidereal day is the time interval between two successive upper culminations of the star through the meridian of the observation point. During a sidereal day, the Earth makes a complete revolution around its axis. They are equal to 23 hours 56 minutes 4 seconds. Sidereal days are used in astronomical observations. true solar day- the time interval between two successive upper culminations of the center of the Sun through the meridian of the observation point. The duration of a true solar day varies throughout the year, primarily due to the uneven movement of the Earth in an elliptical orbit. Hence, they are also inconvenient for measuring time. For practical purposes, they use average solar days. Mean solar time is measured by the so-called mean Sun - an imaginary point that moves uniformly along the ecliptic and makes a complete revolution per year, like the true Sun. The average solar day is 24 hours. They are longer than stellar ones, since the Earth rotates around its axis in the same direction in which it orbits 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 around” by about 1 ° so that the Sun “comes” to the same meridian. Thus, in a solar day, the Earth rotates approximately 361 °. To convert true solar time to mean solar time, an amendment is introduced - the so-called time equation. Its maximum positive value is +14 min on February 11, the largest negative value is -16 min on November 3. The beginning of the average solar day is taken as the moment of the lower climax of the average Sun - midnight. This time count is called civil time.
In everyday life, the average solar time is also inconvenient to use, since it is different on each meridian, the local time. For example, on two neighboring meridians drawn at intervals of 1°, the local time differs by 4 minutes. The presence at various points lying on different meridians of their own local time led to many inconveniences. Therefore, at the International Astronomical Congress in 1884, a zone account of time was adopted. To do this, the entire surface of the globe was divided into 24 time zones, 15 ° each. Per standard time the local time of the middle meridian of each belt is taken. To convert local time to zone time and vice versa, there is a formula Tn – m = N – λ°, where Tp- standard time, m- the local time, N- the number of hours equal to the number of the belt, λ° is longitude expressed in hours. The zero (aka 24th) belt is the one in the middle of which the zero (Greenwich) meridian runs. His time is taken as universal time. Knowing universal time, it is easy to calculate standard time using the formula Tn = T0+N, where T0- universal time. The belts are counted to the east. In two neighboring zones, standard time differs by exactly 1 hour. For convenience, time zone boundaries on land are drawn not strictly along meridians, but along natural boundaries (rivers, mountains) or state and administrative borders.
| In our country, standard time was introduced on July 1, 1919. Russia is located in ten time zones: from the second to the eleventh. However, in order to more rational use summer daylight in our country in 1930, a special government decree introduced the so-called maternity time, ahead of the standard time by 1 hour. So, for example, Moscow is formally located in the second time zone, where the standard time is calculated according to the local time of the meridian 30 ° E. But in fact, the time in winter in Moscow is set according to the time of the third time zone, corresponding to the local time on the meridian 45 ° E. e. Such a “relocation” is valid throughout Russia, except for Kaliningrad region, the time in which 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, the time is moved forward by one hour only for the summer. In Russia, since 1981, for the period from April to October, summer time due to the transfer of time for another hour ahead compared to the maternity. Thus, in summer, the time in Moscow actually corresponds to the local time on the meridian of 60 ° E. e. The time by which residents of Moscow and the second time zone in which it is located live is called Moscow. According to Moscow time in our country, trains and planes are scheduled, the time is marked on telegrams.
In the middle of the twelfth belt, approximately along the 180 ° meridian, in 1884 a international line date changes. This is 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 example, in New Year at 0000 to the west of this line it is already January 1 of the new year, and to the east - only December 31 of the old year. When crossing the border of dates from west to east in the count of calendar days, they return one day ago, and from east to west one day is skipped in the count of dates.
The change of day and night creates daily rhythm in living and inanimate nature. The daily rhythm is associated with light and temperature conditions. The daily course 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 that many plants open their flowers at different hours. According to the time of manifestation of activity, animals can be divided into nocturnal and diurnal: most of them are awake during the day, but many (owls, bats, night butterflies) are in the darkness of the night. Human life also proceeds in a daily rhythm.
Rice. 18. Twilight and white nights
The period of smooth transition from daylight to night darkness and back is called twilight. AT they are based on an optical phenomenon observed in the atmosphere before sunrise and after sunset, when it is still (or already) under the horizon line, but illuminates the sky, from which 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 geographical latitude of the place of observation. At the equator, twilight is short, increasing 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 converges with the morning dawn. In summer they are observed at latitudes of 60° or 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 are observed when the center of the solar disk plunges below the horizon by 6–12°. At the same time, the horizon line is visible, and from the ship it is possible to determine the angle of the stars above it. And finally astronomical twilight are observed when the center of the solar disk submerges below the horizon by 12–18°. At the same time, the dawn in the sky still prevents astronomical observations of faint stars (Fig. 18).
The rotation of the Earth gives two fixed points - geographic poles(points of intersection of the imaginary axis of rotation of the Earth with the earth's surface) - and thus allows you to build a grid of parallels and meridians. Equator(lat. aequator- equalizer) - the line of intersection of the globe with a plane passing through the center of the Earth perpendicular to the axis of its rotation. Parallels(gr. parallelos- going side by side) - the lines of intersection of the earth's ellipsoid by planes parallel to the plane of the equator. meridians(lat. meridlanus- midday) - the lines of intersection of the earth's ellipsoid by planes passing through both of its poles. The length of 1° meridian is on average 111.1 km.
For the nature of the earth's surface, the axial rotation of the earth is of great importance.
1.
It will create the basic unit of time - a day, divided into two main parts - illuminated and unlit. With this unit of time in the process of evolution organic world the physiological activity of animals and plants turned out to be coordinated. The change of tension (work) and relaxation (rest) is an internal need of organisms. Its rhythms could be different, but in the process of evolution there was a selection of such organisms, the internal biological "clock" of which "works" daily.
The main synchronizer of biological rhythms is the alternation of light and darkness. It is associated with the rhythm of photosynthesis, cell division and growth, respiration, the glow of algae and much more.
Since the length of the day varies with the seasons, the daily rhythm in animals and plants varies between 23-26, and in some 22-28 hours.
The most important feature of the thermal regime (and not the amount of heat) of the earth's surface depends on the day - the change of daytime heating and nighttime cooling. It is not only change that is important; but also their duration.
The daily rhythm is also manifested in inanimate nature: in heating and cooling rocks and weathering, temperature conditions of reservoirs, air temperature and winds, ground precipitation.
2.
The second essential meaning of the rotation of geographic space is its division into right and left. This causes the paths of moving bodies to deviate to the right in the northern hemisphere and to the left in the southern.
In 1826, the historian P. A. Slovtsov pointed to the erosion of the right banks of Siberian rivers. In 1857, the Russian academician K. M. Baer expressed general position that all the rivers of the northern hemisphere wash away the right banks. In 1835, the French mathematician G. Coriolis formulated the theory of the relative motion of bodies in a rotating frame of reference. Rotating geographic space is such a mobile system. The deviation of the paths of movement of bodies to the right or to the left is called the Coriolis force or Coriolis acceleration.
The essence of the phenomenon is as follows. The direction of movement of bodies, of course, is rectilinear relative to the axis of the World. But on Earth, it occurs on a rotating sphere, under a moving body the horizon plane turns to the left in the northern hemisphere and to the right in the southern. Since the observer is on a solid surface of a rotating sphere, it seems to him that the moving body is deviated to the right, while in fact the horizon plane is moving to the left.
The Coriolis force can be seen most clearly in the swing of a Foucault pendulum. A load suspended on a free thread oscillates in one plane with respect to the axis of the World. The disk under the pendulum rotates with the Earth. Therefore, each swing of the pendulum with respect to the disk takes place in a new direction. In Leningrad (φ=60°) the disk under the pendulum rotates by 15°sin 60°-13° within an hour, where 15° is the angle of rotation of the Earth during the hour.
The deviation of the path of motion from the original direction of any mass in physical essence is the same as the deviation of Foucault's pendulum.
Conservation by the masses, due to inertia, rectilinear motion and the simultaneous rotation of the earth's surface cause the apparent deviation of the directions of movement to the right in the northern and to the left in the southern hemispheres, regardless of whether the mass moves along the meridian or along the parallel.
Thus, the deflecting force of the Earth's rotation is directly proportional to the mass of the moving body, the speed of movement and the sine of latitude. At the equator, it is 0 and increases with latitude.
All moving masses are subject to the action of the Coriolis force: water in the ocean and sea currents, in rivers, air masses in the process of atmospheric circulation, matter in the Earth's core; Coriolis force is also taken into account in ballistics.
3. The rotation of the Earth (together with the spherical shape) in the field solar radiation(light and heat) determines the west-east extent of natural zones.
4. We have already seen the geodesic (for the figure of the planet) and geophysical (for the redistribution of masses in its body) consequences of the uneven rotational regime of the Earth.
5. Due to the rotation of the Earth, ascending and descending air currents, disordered in different places, acquire predominant helicity: in the northern hemisphere, a left screw is formed, in the southern hemisphere, a right one. Air masses, ocean waters, and also, probably, the substance of the core obey this pattern.
