The basic units of time are year and day. The length of the year is determined by the period of revolution of the Earth around the Sun, and the length of the day is determined by the period of time during which the Earth makes a complete revolution around its axis.
The path along which the Earth makes its annual motion is called its orbit. The Earth's orbit, like the orbits of other planets in the solar system, has the shape of an ellipse. The earth's axis is inclined to the orbital plane at an angle 66°33’. The plane of the earth's equator and the plane of its orbit make an angle 23°27"(Fig. 1).
The period of the Earth's complete revolution around the Sun, i.e. the time interval between two successive passages of the Earth's center through the vernal equinox, is called tropical year.
The point of the vernal equinox is the point in the orbit where the Earth is located on March 21, the autumnal equinox occurs on September 23. At this time, at all latitudes of the Earth, excluding the areas of the Earth's poles, day is equal to night.
A tropical year is equal to 365 days 5 hours 48 minutes 46.1 seconds. For ease of use of the calendar, a year is considered equal to 365 days 6 hours, or three years of 365 days, and every fourth year is 366 days (leap years).
The basic unit of time is taken to be sidereal day- the period between two successive upper culminations of a star (vernal equinox). A sidereal day is 23 hours 56 minutes 4 seconds. During this period of time, the Earth rotates exactly 360°.
In everyday life it is impossible to use sidereal time, since all human activity is inextricably linked with the Sun, and not with the stars. In addition, sidereal days throughout the year begin at different times of the day and night, which is also inconvenient.
Rice. 1 The movement of the Earth around the Sun.
Time can be counted by the apparent movement of the Sun. The period of time between two successive upper culminations of the center of the Sun is called the true solar day. However, it is inconvenient to use them, since the duration of the true sunny day is not constant throughout the year. The reasons for this are the uneven movement of the Sun along the ecliptic and the inclination of the ecliptic to the celestial equator at an angle 23°27’. Therefore, we agreed on the timing; lead relative to the so-called average Sun. The time interval between two successive upper culminations of the average Sun is called the average solar day, but the beginning of the average solar day began to be considered not the moment of the upper (average noon), but the lower culmination (average midnight). Average solar time, counted from the moment of the lower culmination, is called civilian time. It differs from mean solar time by exactly 12 hours
. 
Rice. 2 Time zone map of Eurasia
The mean solar time measured relative to the observer's meridian is called local Tm.
Local time measured from the Greenwich meridian (prime meridian) is called Greenwich Tgr or worldwide.
Using local time in everyday life creates significant inconvenience, since when moving from one point to another, you need to continuously move the clock hands, in accordance with the local time of each point. To avoid this, almost all countries use Standard time Tp.
The essence of standard time is that the entire globe is divided from west to east by meridians into 24 time zones, differing from each other in longitude by 15°. All time zones are widest at the equator; to the north and south they gradually narrow and converge at the poles.
Each belt has its own number: zero, first, second, etc. up to 23 (Fig. 2). The zero belt was chosen based on the position of the Greenwich meridian in the middle of the belt. The numbers of the belts increase in the easterly direction; the difference in longitude between the mean meridians of neighboring time zones is 15°. Consequently, the time difference between each zone is 1 hour. Within the zone, a single time is established, corresponding to the local civil time of the middle meridian of this zone. Since the average meridian of each zone is separated from the extreme meridians by 7.5°, then for points located on the borders of the zone, the zone time differs from their own local time by 0.5 hours.
When crossing the border of the belt, the clock hands are moved exactly one hour forward or backward, depending on which border is being crossed: eastern or western. If the eastern border is crossed, the clock hands are moved forward 1 hour, and if the western border is crossed, the clock hands are moved back 1 hour. In the zero zone, time is calculated according to Greenwich local time.
Time zone boundaries run exactly along the meridians only in deserts and oceans. In the rest of the globe, the boundaries of time zones usually lie along the boundaries of administrative and state divisions; as a result, in some points located on the boundaries of such zones, local time may differ from the standard time of a given zone by more than 30 minutes.
The boundaries of time zones are established by the relevant regulations of the government authorities of each state. Standard time on the territory of our country was introduced by the decree of the Council of People's Commissars of February 8, 1919, signed by V. I. Lenin. On the territory of the USSR, 11 time zones were established - from the second to the twelfth inclusive."
In addition, by decree of the Council of People's Commissars of the USSR dated June 16, 1930, all clocks in our country were moved one hour ahead relative to standard time. This time is called maternity time Td.
Moscow time Tmsk called the time of the middle meridian of the second time zone plus maternity hour.
To move from one time measurement system to another, the following relationships are used:
Тм=Тп +l - N,
Тп=Тм- l + N,
Where Tm- local time of the point;
Tp- standard time of the point;
l- longitude of a given point, expressed in time units;
N-time zone number.
Note. On the territory of the USSR, all points have eastern longitude, and time zones are located east of the zero zone. Therefore, to obtain local time, you need to add longitude expressed in time to standard time and subtract the time zone number.
Converting Moscow time to Greenwich time is done by subtracting the number of the 2nd zone and one hour from Moscow maternity time:
Tgr=Tmsk - (2+1).
To switch from Greenwich time to standard time, you need to add the zone number and maternity hour to Greenwich time:
Tp=Tgr + N+1.
Date line-(time line of demarcation) is a conditionally drawn line running approximately along the 180° meridian along the water surface, skirting islands and capes.
By international agreement, the new date begins on the western side of the demarcation line. On its eastern side, the new date comes only after 24 hours .
Consequently, when crossing the date line from west to east from midnight following the transition of this line, the date is repeated (the calendar shows the same date for two days). At. crossing this line from east to west at midnight, after crossing, its date changes by two units at once (one number drops out of the calendar). Therefore, aircraft crews, when crossing the date line, adhere to the following established procedure for changing the date in the logbook:
when crossing the date line in an easterly direction after a day, the number (date) is repeated;
When crossing the date line in a westerly direction, one is added to the advancing date.
In the Russian Federation, the date line is located on the eastern coast of the Chukotka Peninsula.
Hello dear readers! Today I would like to touch on the topic of the Earth and, and I thought that a post about how the Earth rotates would be useful to you 🙂 After all, day and night, and also the seasons, depend on this. Let's take a closer look at everything.
Our planet rotates around its axis and around the Sun. When it makes one revolution around its axis, one day passes, and when it revolves around the Sun, one year passes. Read more about this below:
Earth's axis.
Earth's axis (Earth's rotation axis) – this is the straight line around which the Earth’s daily rotation occurs; this line passes through the center and intersects the surface of the Earth.
The tilt of the Earth's rotation axis.
The Earth's rotation axis is inclined to the plane at an angle of 66°33´; thanks to this it happens. When the Sun is above the Tropic of the North (23°27´ N), summer begins in the Northern Hemisphere, and the Earth is at its farthest distance from the Sun.
When the Sun rises above the Tropic of South (23°27´ S), summer begins in the Southern Hemisphere.
In the Northern Hemisphere, winter begins at this time. The attraction of the Moon, Sun and other planets does not change the angle of inclination of the earth's axis, but causes it to move along a circular cone. This movement is called precession.
The North Pole now points toward the North Star. Over the next 12,000 years, as a result of precession, the Earth's axis will travel approximately halfway and will be directed towards the star Vega.
About 25,800 years constitute a complete precessional cycle and significantly influence the climate cycle.
Twice a year, when the Sun is directly above the equator, and twice a month, when the Moon is in a similar position, the attraction due to precession decreases to zero and there is a periodic increase and decrease in the rate of precession.
Such oscillatory movements of the earth's axis are known as nutation, which peaks every 18.6 years. In terms of the significance of its influence on climate, this periodicity ranks second after changes in seasons.
The rotation of the Earth around its axis.
Daily rotation of the Earth - the movement of the Earth counterclockwise, or from west to east, as viewed from the North Pole. The rotation of the Earth determines the length of the day and causes the change between day and night.
The Earth makes one revolution around its axis in 23 hours 56 minutes and 4.09 seconds. During the period of one revolution around the Sun, the Earth approximately makes 365 ¼ revolutions, this is one year or equal to 365 ¼ days.
Every four years, another day is added to the calendar, because for each such revolution, in addition to a whole day, another quarter of a day is spent. The Earth's rotation gradually slows down the Moon's gravitational pull, lengthening the day by about 1/1000th of a second every century.
Judging by geological data, the rate of rotation of the Earth could change, but not by more than 5%.
Around the Sun, the Earth rotates in an elliptical orbit, close to circular, at a speed of about 107,000 km/h in the direction from west to east. The average distance to the Sun is 149,598 thousand km, and the difference between the smallest and largest distance is 4.8 million km.
The eccentricity (deviation from the circle) of the Earth's orbit changes slightly over the course of a cycle lasting 94 thousand years. It is believed that the formation of a complex climate cycle is facilitated by changes in the distance to the Sun, and the advance and departure of glaciers during ice ages are associated with its individual stages.
Everything in our vast Universe is arranged very complexly and precisely. And our Earth is just a point in it, but this is our home, which we learned a little more about from the post about how the Earth rotates. See you in new posts about the study of the Earth and the Universe🙂
The Earth makes a complete revolution around its axis in 23 hours 56 minutes. 4 s. The angular speed of all points on its surface is the same and amounts to 15 degrees / h. Their linear speed depends on the distance that the points must travel during the period of their daily rotation. Points on the equator line rotate at the highest speed (464 m/s). The points that coincide with the North and South Poles remain practically motionless. Thus, the linear speed of points lying on the same meridian decreases from the equator to the poles. It is the unequal linear speed of points on different parallels that explains the manifestation of the deflecting action of the Earth’s rotation (the so-called Coriolis force) to the right in the Northern Hemisphere and to the left in the Southern Hemisphere relative to the direction of their movement. The deflecting effect especially affects the direction of air masses and sea currents.
The Coriolis force acts only on moving bodies; it is proportional to their mass and speed of movement and depends on the latitude at which the point is located. The greater the angular velocity, the greater the Coriolis force. The deflecting force of the Earth's rotation increases with latitude. its value can be calculated using the formula
Where m- weight; v- speed of a moving body; w- angular velocity of the Earth's rotation; j- latitude of this point.
The rotation of the Earth causes a rapid cycle of day and night. Daily rotation creates a special rhythm in the development of physical-geographical processes and nature in general. One of the important consequences of the Earth's daily rotation around its axis is the ebb and flow of the tides - the phenomenon of periodic fluctuations in ocean level, which is caused by the gravitational forces of the Sun and Moon. Most of these forces are monthly, and therefore they determine the main features of tidal phenomena. Inflow phenomena also occur in the earth's crust, but here they do not exceed 30-40 cm, while in the oceans in some cases they reach 13 m (Penzhinskaya Bay) and even 18 m (Bay of Fundy). The height of the water projections on the surface of the oceans is about 20 cm, and they circle the oceans twice a day. The extreme position of the water level at the end of the inflow is called high water, at the end of the outflow - low water; the difference between these levels is called the magnitude of the tide.
The mechanism of tidal phenomena is quite complex. Their main essence is that the Earth and the Moon are the only system in rotational motion around a common center of gravity, which lies inside the Earth at a distance of approximately 4800 km from its center (Fig. 10). Like all flesh, the rotating Earth-Moon system is affected by two forces: gravity and centrifugal. The ratio of these forces on different sides of the Earth is not the same. On the side of the Earth facing the Moon, the gravitational forces of the Moon are larger than the centrifugal forces of the system, and their resultant is directed towards the Moon. On the side of the Earth opposite the Moon, the centrifugal forces of the system are larger than the gravitational force of the Moon, and their resultant is directed away from it. These resultants are tidal forces; they cause an increase in water on opposite sides of the Earth.
Rice. 10.
Due to the fact that the Earth rotates daily in the field of these forces, and the Moon moves around it, the inflow waves try to move in accordance with the position of the Moon, therefore, in each region of the ocean for 24 hours 50 minutes. The tide comes in twice and the tide goes out twice. Daily delay of 50 minutes. due to the advancing movement of the Moon in its orbit around the Earth.
The sun also causes tides on Earth, although they are three times lower in height. They are superimposed on the lunar tides, changing their characteristics.
Despite the fact that the Sun, Earth and Moon are almost in the same plane, they continuously change their relative positions in orbits, so their inflow influence changes accordingly. Twice during the monthly cycle - on a new (young) month and a full moon - the Earth, Moon and Sun are on the same line. At this time, the tidal forces of the Moon and the Sun coincide and unusually high, so-called white tides, occur. In the first and third quarters of the Moon, when the tidal forces of the Sun and Moon are directed at right angles to each other, they have the opposite effect and the height of the lunar tides is approximately one third less. These tides are called quadrature.
The problem of using the colossal energy of ebbs and flows has long attracted the attention of mankind, but its solution began with the construction of tidal power plants (TPPs) only now. The first tidal power plant came into operation in France in 1960. In Russia, in 1968, the Kislogubskaya tidal power station was built on the shore of the Kola Bay. It is planned to build several more TPPs in the White Sea area, as well as in the Far Eastern seas of Kamchatka.
The influent waves gradually slow down the speed of the Earth's rotation because they are moving in the opposite direction. Therefore, the earth's day becomes longer. It is calculated that due to water inflows alone, every 40 thousand years the day increases by 1 s. A billion years ago, a day on Earth was only 17 hours long. In a billion years, a day will last 31 hours. And in a few billion years, the Earth will always have one side facing the Moon, just as the Moon is facing the Earth now.
Some scientists believe that the interaction of the Earth with the Moon is one of the main reasons for the initial heating of our planet. The influent friction causes the Moon to move away from the Earth at a speed of about 3 cm/year. This value strongly depends on the distance between the two bodies, which is currently 60.3 Earth radii.
If we assume that at first the Earth and the Moon were much closer, then, on the one hand, the tidal force should be greater. A tidal wave creates internal friction in the body of the planet, which is accompanied by the release of heat,
The Earth's rotation around its axis is associated with its strength, which depends on the angular speed of the planet's daily rotation. Rotation generates centrifugal force, directly proportional to the square of the angular velocity. Now the centrifugal force at the equator, where it is greatest, is only 1/289 of the force of gravity. On average, the Earth has a 15-fold safety margin. The Sun is 200 times, and Saturn is only 1.5 times due to its rapid rotation around its axis. Its rings were formed possibly due to the planet's faster rotation in the past. It was hypothesized that the Moon was formed as a result of the separation of part of the Earth’s mass in the Pacific Ocean due to its rapid rotation. However, after studying samples of lunar rocks, this hypothesis was rejected, but the fact that the shape of the Earth changes depending on the speed of its rotation does not raise any doubt among experts.
The daily rotation of the Earth is associated with such concepts as sidereal, solar, zone and local time, date line, etc. Time is the basic unit for determining the time during which the apparent rotation of the celestial sphere occurs counterclockwise. Having noticed the starting point in the sky, the angle of rotation is calculated from it, from which the elapsed time is calculated. The sidereal hour is counted from the moment of the upper culmination of the vernal equinox, at which the ecliptic intersects the equator. It is used for astronomical observations. Solar time (real, or true, average) is counted from the moment of the lower culmination of the center of the Sun's disk on the observer's meridian. Local time is the average solar time at each point on Earth, which depends on the longitude of that point. The further east a point on Earth is, the longer it has local time (every 15° of longitude gives a time difference of 1 hour), and the further west you go, the shorter the time.
The earth's surface is conventionally divided into 24 time zones, in which time is considered equal to the time of the central meridian, that is, the meridian passing through the middle of the zone.
In densely populated regions, the limits of the belts run along the boundaries of states and administrative regions, sometimes they coincide with natural boundaries: river beds, mountain ranges, and the like. In the first time zone, the time is one hour later than the time of the zero zone, or mean solar time of the Greenwich meridian, in the second zone - by 2:00, etc.
Standard time, which divides the planet into 24 time zones, was introduced in many countries around the world in 1884 p. And although its concentration did not eliminate all misunderstandings related to the calculation of time (let us recall at least the recent heated discussions in some regions of Ukraine regarding the introduction on its territory instead of Moscow Kiev time, that is, the time of a second time zone, in which our country, in fact, located), yet the time zone system has become generally accepted on the planet. After all, standard time not only differs little from local time, it is also convenient when using long distance travel. In this regard, it would be appropriate to recall one interesting story that unexpectedly happened to the participants of the first trip around the world at its completion.
At the end of 1522, an unusual procession walked through the narrow streets of the Spanish city of Seville: 18 sailors from F. Magellan’s expedition had just returned to their home harbor after a long ocean voyage. The people were extremely exhausted during the almost three-year voyage. For the first time they walked around the globe and accomplished a feat. But the winners were not alike. In hands trembling from weakness, they carried burning candles and slowly headed towards the cathedral to atone for the involuntary sin that they committed during the long voyage...
What were the planet's pioneers guilty of? When Victoria approached the Cape Verde Islands on the way back, a boat was sent ashore for food and fresh water. The sailors soon returned to the ship and informed the amazed crew: for some reason on land this day is considered Thursday, although according to the ship's log it is Wednesday. When returning to Seville, they finally realized that they had lost a day in their ship's account! This means that they committed a great sin because they celebrated all religious holidays a day earlier than the calendar required. They repented of this in the cathedral.
How did experienced sailors lose a day? It must be said right away that they did not make any mistake in counting the days. The fact is that the globe rotates around its axis from west to east and every other day makes one revolution. The expedition of F. Magellan moved in the opposite direction from east to west and from After three years of traveling around the world, she also made a full revolution around the earth's axis, but in the direction opposite to the direction of the Earth's rotation, which means that the travelers made one revolution less than all of humanity on Earth. And they did not lose a day, but won it. If If the expedition had moved not to the west, but to the east, then the ship's log would have recorded one day more than all the people.The astronomer of F. Magellan's expedition, Antonio Pigafetta, guessed that in different places on the globe at the same moment time different. And so it should be, because the Sun does not rise at the same time for the entire planet. This means that on each meridian there is local time, the beginning of which is counted from the moment when the Sun is low below the horizon, that is, it is in the so-called lower climax. However, people in their daily activities do not pay attention to this and focus on the standard time corresponding to the local time of the median meridian of the corresponding time zone.
But dividing the globe into time zones still does not solve all the problems, in particular the problem of rational use of the light period. Therefore, on the last Sunday of March in many countries, including Ukraine, the clock hands are moved forward one hour, and at the end of October they are returned to standard time. The transition to summer time allows for more economical use of fuel and energy resources. In addition, this gives people the opportunity to work and relax more in natural light, and to use the darkest time of day for sleep.
In the practical distribution of time zones on our planet, the spaces through which the date line conventionally passes are specific. This line runs mostly in the open ocean along the 180° meridian and deviates somewhat where it crosses islands or separates different states. This was done to avoid certain calendar inconveniences for the people who inhabit them. When crossing a line from west to east, the date is repeated; when moving in the opposite direction, one day is excluded from the count. Interestingly, in the Bering Strait between Chukotka and Alaska there are two islands that are separated by the International Date Line: Ratmanov Island, which belongs to Russia, and Kruzenshtern Island, which belongs to SELA. Having covered a distance of several kilometers between two islands, you can find yourself... in yesterday, if you are sailing from Ratmanov Island, or in tomorrow, when heading in the opposite direction.
The Earth makes a few different movements: together with the Galaxy towards the constellations Lyra and Hercules at a speed of 20 km/sec., rotational movement relative to the Center of the Galaxy with V = 250-280 km/sec., around the sun at a speed of 30 km/sec., around its axis with speed 0.5 km/sec. etc. This complex system of movements causes a number of phenomena on earth, formulating natural conditions. Let's consider only 2 movements that are important for the environment and humans.
Daily rotation.
When observing the sun and planets from the Earth, it seems that the Earth is motionless, and the sun and planets rotate around it (the effect of a moving station). It was precisely this model (geocentric), authored by Ptolemy (2nd century BC) that existed until the 16th century. However, as evidence accumulated, this model began to be questioned. The first person to publicly speak out against it was the Pole Nicolaus Copernicus. After his death, Copernicus' ideas were developed by the Italian Giordano Bruno, who was burned at the stake because... refused to cooperate with the Inquisition. His compatriot Galileo continued to develop the ideas of Copernicus and Bruno and, with the help of the telescope he invented, confirmed the correctness of his own.
Thus, already at the beginning of the 17th century. The rotation of the Earth around its axis was proven. Currently, no one doubts this fact and we have many evidence of axial rotation.
One of the simplest and most convincing is the experiment with the Foucault pendulum. In 1851 the Frenchman L. Foucault, using a huge pendulum, showed that the plane of the pendulum always shifts clockwise (when viewed from above). If the Earth did not rotate from west to east (counterclockwise), then such an effect with a pendulum would not exist.
The second convincing evidence of the axial rotation of the Earth is the deflection of falling bodies to the east, i.e. if you drop a load from a high tower, it will fall to the Earth, deviating from the vertical by several mm. or cm depending on height.
The globe rotates around its axis - just like all planets rotate around their axes. Moreover, everyone almost rotates in the same direction as around the Sun. Those places where the axis of rotation of the planets intersects with their surface are called poles (for the Earth - geographic poles, South and North). A line passing along the surface of the planet at an equal distance from both poles is called the equator.
Geographic poles do not remain in one place, but move across the surface of the planet. Fortunately for us, not very far and not very fast.
Observations at stations of the International Pole Movement Service (until 1961 it was called the International Latitude Service; it was created in 1899), as well as twenty years of measurements using geodetic satellites indicate that the geographic poles are moving at a speed of 10 cm. in year.
What consequences are associated with the daily rotation of the Earth?
Firstly, it is the change of day and night. Moreover, due to the comparative interval between day and night, the atmosphere and surface of the Earth do not have time to supercool and heat up. The change of day and night, in turn, causes the rhythm of many processes in nature (biorhythms).
Secondly, an important consequence of rotation is the deflection of horizontally moving bodies to the right in the northern hemisphere and to the left in the southern hemisphere. Deflection force or Coriolis force is associated with a time shift in the direction of meridians and parallels. At the pole, where the parallels and meridians are almost parallel to each other, this force is zero, and at the equator, where they are at the greatest angle, the force is maximum.
The Coriolis effect is of great importance for objects moving for a long time in the meridional direction (river waters, air masses, etc.) this effect becomes noticeable: rivers wash away one of the banks more than the other. And the winds, which have been blowing in one direction for a long time, noticeably shift. The most important manifestation of such a shift is the twisting of winds in zones of high (anticyclones) and low (cyclones) atmospheric pressure.
Third, an important consequence is the ebb and flow of tides. As the Earth rotates, it periodically falls under the gravitational pull of the Moon, resulting in a tidal wave. During the new moon and full moon, the tides are at their maximum; during the 1/4 phase of the moon they are at their minimum.
The rotation of the Earth has long been used to count time. A complete rotation of the Earth around its axis occurs in different periods of time depending on the starting point. Relative to the stars, a complete rotation occurs in 23 hours. 56min.4sec. (sidereal day). And relative to the sun - in 24 hours. (solar day). However, these are average solar days, since clear solar days vary throughout the year.
In addition to local time (average solar day), which depends on the position of the local meridian relative to the sun, there is a standard time system. In this regard, the entire globe is divided into 24 zones, with zero, which passes through the Greenwich meridian. Each zone differs in time from the neighboring one by 1 hour. In the east, 1 hour more, and in the west, 1 hour less.
Apparent movement of the sky. It is known that the celestial bodies are located at very different distances from the globe. At the same time, it seems to us that the distances to the luminaries are the same and that they are all associated with one spherical surface, which we call the vault of heaven, and astronomers call the visible celestial sphere. It seems so to us because the distances to the celestial bodies are very large, and our eye is not able to notice the difference in these distances. Every observer can easily notice that the visible celestial sphere with all the bodies located on it slowly rotates. This phenomenon has been well known to people since ancient times, and they took the apparent movement of the Sun, planets and stars around the Earth as reality. Currently, we know that it is not the Sun or the stars that move around the Earth, but that the globe rotates.
Accurate observations have shown that the Earth completes its revolution around its axis in 23 hours 56 minutes. and 4 sec. We take the time of a complete rotation of the Earth around its axis as a day and, for simplicity, count 24 hours in a day.
Evidence of the Earth's rotation around its axis. We now have a number of very convincing evidence of the Earth's rotation. Let us first dwell on the evidence arising from physics.
Foucault's experience. In Leningrad, in the former St. Isaac's Cathedral, a pendulum with 98 m length, with a load of 50 kg. Below the pendulum is a large circle divided into degrees. When the pendulum is in a calm position, its load is located exactly in the center of the circle. If you take the weight of the pendulum to the zero degree of the circle and then let it go, then the pendulum will swing in the plane of the meridian, that is, from north to south. However, after 15 minutes the swing plane of the pendulum will deviate by approximately 4°, after an hour by 15°, etc. It is known from physics that the swing plane of the pendulum cannot deviate. Consequently, the position of the graduated circle changed, which could only happen as a result of the daily movement of the Earth.
To understand the essence of the matter more clearly, let us turn to the drawing (Fig. 13, a), which depicts the northern hemisphere in polar projection
The meridians extending from the pole are indicated by a dotted line. Small circles on the meridians are a conventional image of a graduated circle under the pendulum of St. Isaac's Cathedral. In the first position ( AB) the swing plane of the pendulum (indicated by a solid line in a circle) completely coincides with the plane of this meridian. After some time the meridian AB due to the rotation of the Earth from west to east, it will be in position A 1 B 1. The plane of swing of the pendulum remains the same, due to which the angle between the plane of swing of the pendulum and the plane of the meridian is obtained. With further rotation of the Earth, the meridian AB will be in a position A 2 B 2 etc. It is clear that the swing plane of the pendulum will deviate even more from the plane of the meridian AB. If the Earth was stationary, such a divergence could not happen, and the pendulum would swing from beginning to end in the direction of the meridian.
A similar experiment (on a smaller scale) was first carried out in Paris in 1851 by the physicist Foucault, which is why it got its name.
Experiment with deflection of falling bodies to the east. According to the laws of physics, a load must fall from a height along a plumb line. However, in all experiments performed, the falling body invariably deviated to the east. The deviation occurs because when the Earth rotates, the speed of a body moving from west to east at an altitude is greater than at the level of the earth's surface. The latter can be easily understood from the attached drawing (Fig. 13, b). A point located on the earth's surface moves with the Earth from west to east and covers the path over a certain period of time BB 1. A point located at a certain height travels a path during the same period of time AA 1. Body thrown from a point A, moves faster at altitude than a point IN, and during the time the body falls, point A will move to point A 1 and a body with high speed will fall east of point B 1. According to experiments, a body falling from a height of 85 m deviated from the plumb line to the east by 1.04 mm, and when falling from a height of 158.5 m- by 2.75 cm.
The rotation of the Earth is also indicated by the oblateness of the globe at the poles, the deviation of winds and currents in the northern hemisphere to the right, and in the southern hemisphere to the left, which will be discussed in more detail later.
The rotation of the Earth makes it clear to us why the polar oblateness of the Earth does not cause the water masses of the oceans to move from the equator to the poles, i.e., to the position closest to the center of the Earth (centrifugal force keeps these waters from moving to the poles), etc.
Geographical significance of daily rotationof the Earth. The first consequence of the Earth's rotation around its axis is the change of day and night. This change is quite fast, which is very important for the development of life on Earth. Due to the shortness of day and night, the Earth can neither overheat nor overcool to such limits that life would be killed either by excessive heat or excessive cold.
The change of day and night determines the rhythm of many processes on Earth associated with the inflow and outflow of heat.
The second consequence of the rotation of the Earth around its axis is the deviation of any moving body from its original direction in the northern hemisphere to the right, and in the southern hemisphere to the left, which is of great importance in the life of the Earth. We cannot give a complex mathematical proof of this law here, but we will try to give some, albeit very simplified, explanation.
Let us assume that the body received a rectilinear motion from the equator to the North Pole. If the Earth did not rotate around its axis, then a moving body c. in the end it would end up at the pole. However, this does not happen on Earth because the body, being at the equator, moves with the Earth from west to east (Fig. 14, a). Moving towards the pole, the body becomes more
high latitudes, where every point on the earth's surface moves from west to east more slowly than at the equator. A body moving towards the pole, according to the law of inertia, maintains the speed of movement from west to east that it had at the equator. As a result, the path of the body will always deviate from the direction of the meridian to the right. It is not difficult to understand that in the southern hemisphere, under the same conditions of movement, the path of the body will deviate to the left (Fig. 14.6).
Poles, equator, parallels and meridians. Thanks to the same rotation of the Earth around its axis, we have two wonderful points on Earth, which are called poles. The poles are the only fixed points on the earth's surface. Based on the poles, we determine the location of the equator, draw parallels and meridians and create a coordinate system that allows us to determine the position of any point on the surface of the globe. The latter, in turn, gives us the opportunity to plot all geographical objects on maps.
A circle formed by a plane perpendicular to the earth's axis and dividing the globe into two equal hemispheres is called equator. The circle formed by the intersection of the equatorial plane with the surface of the globe is called the equator line. But in colloquial speech and geographical literature, the equator line is often called simply the equator for brevity.
The globe can be mentally intersected by planes parallel to the equator. This produces circles called parallels. It is clear that the sizes of parallels for the same hemisphere are not the same: they decrease with distance from the equator. The direction of the parallel on the earth's surface is the exact direction from east to west.
The globe can be mentally dissected by planes passing through the earth's axis. These planes are called meridian planes. Circles formed by the intersection of meridian planes with the surface of the globe are called meridians. Every meridian inevitably passes through both poles. In other words, the meridian everywhere has the exact direction from north to south. The direction of the meridian at any point on the earth's surface is most simply determined by the direction of the midday shadow, which is why the meridian is also called the midday line (lat. rneridlanus, which means midday).
Latitude and longitude. The distance from the equator to each of the poles is a quarter of a circle, i.e. 90°. Degrees are counted along the meridian line from the equator (0°) to the poles (90°). The distance from the equator to the North Pole, expressed in degrees, is called northern latitude, and to the South Pole - southern latitude. Instead of the word latitude, for brevity, they often write the sign φ (the Greek letter “phi”, northern latitude with a + sign, southern latitude with a - sign), for example, φ = + 35°40".
When determining the degree distance to the east or west, counting is carried out from one of the meridians, which is conventionally considered to be zero. According to international agreement, the prime meridian is considered to be the meridian of the Greenwich Observatory, located on the outskirts of London. The degree distance to the east (from 0 to 180°) is called east longitude, and to the west - west longitude. Instead of the word longitude, they often write the sign λ (the Greek letter “lambda”, eastern longitude with a + sign, and western longitude with a - sign), for example, λ = -24°30 /. Using latitude and longitude, we are able to determine the position of any point on the earth's surface.
Determining latitude at Earth. Determining the latitude of a place on Earth comes down to determining the height of the celestial pole above the horizon, which can be easily seen from the drawing (Fig. 15). The easiest way in our hemisphere to do this is with the help of the North Star, which is located just 1 o 02" from the celestial pole.
An observer at the North Pole sees the North Star just overhead. In other words, the angle formed by the ray of the North Star and the plane of the horizon is equal to 90°, i.e. exactly corresponds to the latitude of a given place. For an observer located at the equator, the angle formed by the ray of the North Star and the horizon plane should be equal to 0°, which again corresponds to the latitude of the place. When moving from the equator to the pole, this angle will increase from 0 to 90° and will always correspond to the latitude of the place (Fig. 16).
It is much more difficult to determine the latitude of a place from other luminaries. Here you have to first determine the height of the luminary above the horizon (i.e., the angle formed by the ray of this luminary and the plane of the horizon), then calculate the upper and lower culmination of the luminary (its position at 12 noon and 0 a.m.) and take the arithmetic average between them. For calculations of this kind, special rather complex tables are required.
The simplest device for determining the height of a star above the horizon is a theodolite (Fig. 17). At sea, in rolling conditions, a more convenient sextant device is used (Fig. 18).
The sextant consists of a frame, which is a sector of a circle of 60°, i.e. constituting 1/6 of the circle (hence the name from the Latin sextans- sixth part). A small telescope is mounted on one spoke (frame). On the other knitting needle there is a mirror A, half of which is covered with amalgam and the other half is transparent. Second mirror IN attached to the alidade, which serves to measure the angles of the graduated dial. The observer looks through the telescope (point O) and sees through the transparent part of the mirror A horizon I. Moving the alidade, he catches on the mirror A image of the luminary S, reflected from the mirror IN. From the attached drawing (Fig. 18) it is clear that the angle SOH (determining the height of the luminary above the horizon) is equal to double the angle CBN.
Determination of longitude on Earth. It is known that each meridian has its own, so-called local time, and a difference of 1° longitude corresponds to a 4-minute time difference. (A complete revolution of the Earth around its axis (360°) takes 24 hours, and a rotation of 1° = 24 hours: 360°, or 1440 minutes: 360° = 4 minutes.) It is easy to see that the time difference between the two points allows you to easily calculate the difference in longitudes. For example, if at this point it is 13 o'clock. 2 minutes, and on the zero meridian it is 12 hours, then the time difference = 1 hour. 2 minutes, or 62 minutes, and the difference in degrees is 62:4 = 15°30 / . Therefore, the longitude of our point is 15°30 / . Thus, the principle of calculating longitudes is very simple. As for methods for accurately determining longitude, they present significant difficulties. The first difficulty is accurately determining local time astronomically. The second difficulty is the need
to have accurate chronometers. Recently, thanks to radio, the second difficulty has been greatly alleviated, but the first remains valid.