Daily rotation of the earth. Rotation of the starry sky Rotation of the sky
FUNDAMENTALS OF SPHERICAL AND PRACTICAL ASTRONOMY
CHAPTER 1
The meaning of astronomy
Astronomy and its methods are of great importance in the life of modern society. Issues related to the measurement of time and providing humanity with knowledge of the exact time are now being resolved by special laboratories - time services, organized, as a rule, at astronomical institutions.
Astronomical orientation methods, along with others, are still widely used in navigation and aviation, and in recent years - in astronautics.
The calculation and compilation of the calendar, which is widely used in the national economy, is also based on astronomical knowledge.
Drawing up geographical and topographic maps, pre-calculating the onset of sea tides, determining the force of gravity at various points on the earth's surface in order to detect mineral deposits - all this is based on astronomical methods.
Studies of processes occurring on various celestial bodies allow astronomers to study matter in states that have not yet been achieved in earthly laboratory conditions. Therefore, astronomy, and in particular astrophysics, which is closely related to physics, chemistry, and mathematics, contributes to the development of the latter, and they, as we know, are the basis of all modern technology.
Astronomy, by studying celestial phenomena, exploring the nature, structure and development of celestial bodies, proves that the Universe is subject to the uniform laws of nature and, in accordance with them, develops in time and space. Therefore, the conclusions of astronomy have deep philosophical significance.
No matter where we are on the earth’s surface, it always seems to us that all celestial bodies are located at the same distance from us on the inner surface of a certain sphere, which is colloquially called firmament , or simply sky .
During the day, the sky, if it is not covered by clouds, is blue, and we see the brightest celestial body on it - the Sun. Sometimes, simultaneously with the Sun, the Moon is visible during the day and very rarely some other celestial bodies, for example, the planet Venus.
On a cloudless night in the dark sky we see stars, the Moon, planets, nebulae, sometimes comets and other bodies. The first impression from observing the starry sky is the countless number of stars and the randomness of their arrangement in the sky. In reality, there are not as many stars visible to the naked eye as it seems, only about 6 thousand in the entire sky, and in one half of it, which is currently visible from any point on the earth’s surface, no more than 3 thousand.
Stars have two properties: 1) they differ in brightness from each other; 2) relatively motionless. These properties make it possible to distinguish star figures in the sky, called constellations.
The system of constellations in our sky was created 500 years BC. by the ancient Greeks.
The constellations were designated by the names of animals ( Ursa Major, Leo, Dragon etc.), names of heroes of Greek mythology ( Cassiopeia, Andromeda, Perseus etc.) or simply the names of those objects that resembled the figures formed by the bright stars of the group ( Northern Crown, Triangle, Arrow, Libra and so on.).
Since the 17th century individual stars in each constellation began to be designated by letters of the Greek alphabet, and, as a rule, in descending order of their brightness. Somewhat later, numerical numbering was introduced, which is currently used mainly for faint stars. In addition, bright stars (about 130) received their own names. For example: a Canis Major is called Sirius, a Auriga - Capella, a Lira - Vega, a Orion - Betelgeuse, b Orion - Rigel, b Perseus - Algolem etc. These names and designations of stars are still used today. However, the boundaries of the constellations, outlined by ancient astronomers and representing winding lines, were changed at the astronomical congress in 1922, some large constellations were divided into several independent constellations, and constellations began to be understood not as figures of stars, but as sections of the starry sky. Now the entire sky is conventionally divided into 88 separate sections - constellations.
The brightest stars in the constellations serve as good guides for locating fainter stars or other celestial objects in the sky.
If you observe the starry sky for several hours on a clear night, it is easy to notice that the vault of heaven, as one whole, with all the luminaries located on it, smoothly rotates around some imaginary axis, one end of which passes through the place of observation, and the other is very close near Polar stars. This rotation of the firmament and luminaries is called daily movement of the starry sky , since one complete circulation is completed per day. Due to daily rotation, stars and other celestial bodies continuously change their position relative to the sides of the horizon and describe circles around the axis of rotation.
Announcement: What is the most basic, earliest factor in the historical hierarchy of development and progress, without which life itself could not have appeared on Earth? I’ll say right away - this factor is the daily rotation of the Earth around its axis! Without daily rotation, life could never have appeared on Earth! But the reason for the daily rotation of the Earth around its axis has not yet been revealed, and scientists still do not know what spun and continues to spin our planet, divine will or a material reason.
There are many unsolved mysteries and mysteries of the universe, and the more we understand the world around us, the more new ideas, mysteries and questions appear. But these new mysteries in the hierarchy of development are more recent, i.e. derived from more important primary forms and laws. And some important primary mysteries have not yet been solved even today. For example, what is the most basic, key factor in the historical hierarchy of development and progress, without which life itself could not have appeared on Earth?
I’ll say right away - one of the most important and greatest factors is the factor of the Earth’s daily rotation. Yes Yes! If there were no daily rotation of the Earth, then life could never have arisen on Earth! And the mystery of the mechanism by which this rotation occurs has not yet been solved. Let's understand some facts: the power of solar radiation when approaching the Earth is huge ~ 1.5 kWh/m2 and without rotation around its axis, one side of the Earth would be heated by the radiation of the Sun, and on the other side cosmic cold would reign! The heat of the Sahara and the cold of Antarctica would be many times stronger! And it was the daily rotation of the Earth that made it possible to make thermal conditions more uniform over millions of years in all regions of the Earth, and this was one of the most important conditions for the emergence of life. Those. The daily rotation of the Earth was the key, main condition for the emergence of life on Earth.
But how did this daily rotation come about? What spun our planet? Today there is no scientific explanation for this mystery! The daily rotation of the Earth itself was scientifically proven by historical standards quite recently, in the period from the 14th to the 16th centuries AD, together with the creation of the heliocentric system of the world and the discovery of the Earth’s rotation around the Sun. Before this, for thousands of years, the idea of the Earth as the immovable center of the whole world prevailed. Understanding the questions raised by the theory of the rotating Earth contributed to the discovery of the laws of classical mechanics.
An experiment clearly demonstrating the rotation of the Earth was carried out in 1851 by the French physicist Leon Foucault. Its meaning is very simple and clear. The plane of oscillation of a pendulum is constant relative to the fixed stars. And in the reference system associated with the Earth, the plane of oscillation of the pendulum rotates in the direction opposite to the direction of rotation of the Earth, which is clearly visible from the divisions on the circle placed under the pendulum. This effect is most clearly expressed at the poles, where the period of complete rotation of the pendulum’s plane is equal to the period of the Earth’s rotation around its axis, and at the equator the plane of oscillation of the pendulum is unchanged. Currently, the Foucault pendulum is successfully demonstrated in a number of scientific museums and planetariums, in particular, in the St. Petersburg Planetarium and the Volgograd Planetarium.
In recent years, one hypothesis has emerged regarding the origin of the Earth’s daily rotation from the action of global terrestrial winds and ocean currents, but it does not stand up to criticism. After all, water and atmosphere on Earth appeared much later than the appearance of the Earth’s daily rotation. In addition, scientists have proven that ocean currents appeared precisely due to the daily rotation of the Earth, and not vice versa. The influence of the Moon also could not lead to the appearance of the Earth's daily rotation. In addition, the Moon has its own rotation. Other planets of the solar system, as well as the Sun itself, also rotate around their axis. What's causing all this spinning? No answer yet. But perhaps the mechanism for the occurrence of rotation of the planets and the Sun is the same, since the Sun rotates around the center of the Milky Way galaxy, like the planets around the Sun. 
By the way, all celestial bodies rotate not in a circle, but in an elliptical Keplerian orbit, which also shifts in space over time: 
Also, there is no answer yet to the question of the reason for the appearance of the tilt of the Earth’s rotation axis relative to the plane of the Earth’s rotation around the Sun. This tilt is 66˚33’22” and its presence led to the appearance of seasons on Earth that are extremely important for the Earth’s climate.
The seasons, along with the daily rotation, i.e. the rapid change of day and night, further softened and facilitated the conditions for the emergence of life and the Earth’s biosphere, for the emergence of numerous forms of plants, animals, and humans. Together with the seasons, 5 zones of illumination (or radiation) arose on Earth, limited by the tropics and polar circles, which are divided according to the duration of sunlight and the amount of heat received. Scientists have also noticed that the Earth's rotation axis periodically changes its direction. This is called precession. Every 13 thousand years, the Earth's rotation axis "tilts" in the opposite direction. But huge celestial bodies rotating in zero gravity are ideal gyroscopes that cannot change their orientation in space. 
Only long after the emergence of daily rotation, water, an oxygen atmosphere, and then various forms of life, animals, plants, and humans appeared on Earth.
Another important factor for the emergence of life on Earth is the Earth's magnetic field. The Earth's magnetosphere protects all living things from solar radiation. But this factor has long found its scientific explanation. So I'll touch on it very briefly.
The Sun and each planet of the Solar System has its own magnetic field, which creates a special shell around each of these celestial bodies - the magnetosphere. The poles of the Earth's magnetic field are located almost on the axis of the Earth's daily rotation with a slight deviation of 11.5 degrees from it. There are two types of the Earth's magnetic field: constant (main) and variable. Their nature and origin are different, but there is a relationship between them. The formation of a constant magnetic field is facilitated by internal sources of the Earth - electric currents arising on the surface of the compacted core of the Earth due to temperature differences in its parts, which is presumably associated with dynamic processes in the mantle and core of the Earth. They create a stable magnetic field extending over 20-25 Earth radii, which is subject only to slow, “secular” fluctuations. An alternating field is created when interacting with external sources located outside the planet. An alternating magnetic field is approximately 100 times weaker than a constant one and is characterized by regular variations, mainly of a solar nature, and irregular ones (such as magnetic storms). The Earth's average magnetosphere diameter is over 90 thousand km perpendicular to the sun's ray. The Earth is constantly exposed to streams of charged particles (corpuscles) of cosmic origin and radiation from the Sun - the solar wind. The magnetosphere under the impacts of the solar wind is compressed from the side of the Sun and is strongly elongated in the antisolar direction. This is how the tail of the magnetosphere is formed, extended to 900-1050 Earth radii. The magnetosphere is the main obstacle to the penetration of charged solar particles harmful to living matter into the geographic envelope and thus isolates living organisms from penetrating radiation. Cosmic particles can freely invade the atmosphere only in the region of the magnetic poles. At the same time, the magnetosphere transmits electromagnetic waves to the surface of the planet - X-rays and ultraviolet rays, radio waves and radiant energy, which serves as the main source of heat and the energy base for the processes occurring in the geographic envelope. 
In the historical context, geographic shifts of the magnetic field and even changes in the polarity of the magnetic dipole are observed. Polarity, when the northern end of the magnetic needle is directed to the north, is called direct (as it is now); in the opposite case, they speak of reverse magnetization of the earth's dipole. Observations of the Earth's magnetic field are carried out by many observatories around the world.
Thus, the rotation of planets around their axis is the most important and most important condition for the emergence of life on planets. Finding out the reason for the planets’ own rotation will make it possible to understand whether there can be many planets like the Earth in the Universe, on which life will also appear over time, or whether the Earth is a unique phenomenon in the Universe. The presence of daily rotation on other planets of the Solar System hints that the reason for the appearance of such rotation on the planets is not an accident, but some as yet undiscovered objective mechanism that is awaiting scientific discovery. And this means that the Hierarchy of the laws of the origin and development of the world is just beginning to be cognized by man.
Additional information on this topic:
Solar system bodies | Average Distance to the Sun, a. e. | Average period of rotation around an axis | Number of phases of the state of matter on the surface | Number of satellites | Sidereal period of revolution, year | Orbital inclination to the ecliptic | Mass (unit of Earth mass) |
Sun | 25 days (35 at the pole) | 1 | 9 planets | 333000 |
|||
Mercury | 0,387 | 58.65 days | 2 | - | 0,241 | 0,054 |
|
Venus | 0,723 | 243 days | 2 | - | 0,615 | 3°24’ | 0,815 |
Earth | 23 h 56m 4s | 3 | 1 | ||||
Mars | 1,524 | 24h 37m 23s | 2 | 2 | 1,881 | 1°51’ | 0,108 |
Jupiter | 5,203 | 9h 50m | 3 | 16+p.ring | 11,86 | 1° 18’ | 317,83 |
Saturn | 9,539 | 10h 14m | 3 | 17+rings | 29,46 | 2°29’ | 95,15 |
Uranus | 19,19 | 10h 49m | 3 | 5+knot rings | 84,01 | 0 ° 46’ | 14,54 |
Neptune | 30,07 | 15h 48m | 3 | 2 | 164,7 | 1° 46’ | 17,23 |
Pluto | 39,65 | 6.4 days | 2- 3 ? | 1 | 248,9 | 17° | 0,017 |
The geographical consequences of the Earth's daily rotation are:
1. Change of day and night.
2. Deformation of the Earth's figure.
3. The existence of the Coriolis force acting on moving bodies.
4. The occurrence of ebbs and flows. 
« About the reason for the rotation of the Earth and other unexplained phenomena.
habar Space scientist
Date: Sunday, 20.11.2011, 19:55
During the day the Sun moves across the sky. It rises, rises higher and higher, then begins to descend and sets. It is not difficult to see that the stars also move across the sky.
Choose a place for observation from where the sky is clearly visible, and note from it over which objects visible on the horizon (houses or trees) the Sun is visible in the morning, at noon and in the evening. Come to this place after sunset, notice the brightest stars in the same directions of the sky and mark the time of observation on the clock. If you come to the same place an hour or two later, make sure that all the stars you noticed have moved from left to right. So, the star that was in the direction of the morning Sun rose in the sky, and the star that was in the direction of the evening Sun sank.
Do all the stars move across the sky? It turns out, everything, and at the same time. We can say that the entire sky with the stars in it seems to revolve around us every day.
The side of the sky where the Sun is visible at noon is called the southern side, and the opposite side is called the northern side. Look in the northern sky, first at the stars close to the horizon, and then at the higher ones. You will see that the higher the stars are from the horizon, the less noticeable their movement. You can also find a star in the sky whose movement throughout the night is almost imperceptible, and the closer other stars are to this star, the less noticeable their movement is. This star was called Polar, we already know how to find it from the stars of Ursa Major.
When we look at the North Star, or more precisely, at a fixed point next to it - at the north pole of the world, the direction of our gaze coincides with the direction of the axis of the starry sky. The axis of rotation of the starry sky itself is called the axis of the world.
The rotation of the sky around the Earth is an apparent phenomenon. The reason for this is the rotation of the Earth. Just as a person spinning around a room seems as if the whole room is spinning around him, so to us, who are on a rotating Earth, it seems that the sky is spinning. In ancient times, observing the daily rotation of the sky, people made a deeply erroneous conclusion that the stars, the Sun and the planets revolve around the Earth every day. In fact, as it was established in the 16th century. Copernicus, the apparent rotation of the starry sky is only a reflection of the daily rotation of the Earth around its axis. However, the stars still move. Not so long ago, astronomers found that all the stars of our Galaxy move at different speeds around its center (the Galaxy is described in the article “3 Stars and the Depths of the Universe”).
The imaginary axis around which the globe rotates intersects the Earth's surface at two points. These points are the North and South geographic poles. If we continue the direction of the earth's axis, it will pass near the North Star. This is why the North Star seems almost motionless to us.
In the southern starry sky, which in our northern hemisphere is only partially visible due to the spherical shape of the Earth, there is a second fixed point in the sky - the south celestial pole. The stars of the southern hemisphere revolve around this point.
Let's take a closer look at the apparent daily motion of stars. Turn your face to the southern side of the horizon and watch the movements of the stars. To make observations more convenient, imagine a semicircle that passes through the zenith (the point directly above your head) and the celestial pole. This semicircle (celestial meridian) will intersect with the horizon at the point of the north (under the North Star) and at the opposite point of the south. It divides the sky into eastern and western halves. Observing the movement of stars in the southern part of the sky, we will notice that the stars located to the left of the celestial meridian (i.e., in the eastern part of the sky) rise above the horizon. Having passed through the celestial meridian and entering the western part of the sky, they begin to descend towards the horizon. This means that when the stars pass through the celestial meridian, they reach their greatest height above the horizon. Astronomers call the passage of a star through its highest position above the horizon the upper culmination of that star.
If you turn your face to the north and begin to observe the movements of the stars in the northern part of the sky, you will notice that the stars passing through the celestial meridian below the North Star at this moment occupy the lowest position above the horizon. Moving
from left to right, they, having passed the celestial meridian, begin to rise. When a star passes through its lowest possible position above the horizon, astronomers say the star is at its lowest climax.
Among the constellations visible in our country, there are those that, moving around the celestial pole, never go beyond the horizon. This is easy to verify by observation: in the winter months, the constellation Ursa Major is visible above the horizon at its lowest position during the day.
But not only the Big Dipper turns out to be a non-setting constellation for the inhabitants of the USSR. The stars Ursa Minor, Cassiopeia, Draco, Cepheus, located close to the north pole of the world, also never go, for example, beyond the Moscow horizon. These are never setting stars.
Along with the stars that never set, there are also those that never rise over our country. These include many stars in the southern hemisphere of the sky.
The sky, like the globe, is mentally divided into two hemispheres by an imaginary circle, all points of which are at the same distance from the poles of the world. This circle is called the celestial equator. It crosses the horizon at the east and west points.
All stars during the day describe paths parallel to the celestial equator. The hemisphere of the sky in which the North Star is located is called the northern hemisphere, and the other hemisphere is called the southern hemisphere.
View of the starry sky in different places on Earth
The sky looks different in different places around the world. It turns out that the appearance of the starry sky depends on what parallel the observer is at, in other words, what is the geographic latitude of the observation site. The angular elevation of the celestial pole (or, approximately, the North Star) above the horizon is always equal to the geographic latitude of the place.
If you take a trip to the North Pole from Moscow, you will notice as you go that the North Star (or celestial pole) is getting higher and higher above the horizon. Therefore, more and more stars turn out to be non-setting.
Finally, you have arrived at the North Pole. Here the arrangement of stars is not at all the same as in the Moscow sky.
The geographic latitude of the North Pole of the globe is 90°. This means that the celestial pole (and the North Star) will be directly overhead - at the zenith. It is not difficult to imagine that the celestial equator will coincide with the horizon here at the North Pole. Thanks to this, at the North Pole you will see an unusual picture of the movement of stars: always moving along paths parallel to the celestial equator, the stars move parallel to the horizon. Here all the stars in the northern hemisphere of the sky will be non-setting, and all the stars in the southern hemisphere will be non-rising.
If you now mentally transport yourself from the North Pole to the earth's equator, you will see a completely different picture.
As you move south, the latitude of the place and therefore the height of the celestial pole (and Polaris) will begin to decrease, i.e. Polaris will approach the horizon.
When you find yourself on the earth's equator, the geographic latitude of any point of which is zero, you will see the following picture: the north pole of the world will find itself at the north point, and the celestial equator will become perpendicular to the horizon. At the south point there will be the south celestial pole, located in the constellation Octantus.
All stars on the earth's equator describe paths perpendicular to the horizon during the day. If there were no Sun, because of which it is impossible to see the stars during the day, then during the day at the earth's equator it would be possible to observe all the stars of both hemispheres of the sky.
At different times of the year, different constellations can be observed in the evenings. Why is this happening?
To understand this, make some observations. Shortly after sunset, notice a star in the western sky low above the horizon and remember its position in relation to the horizon. If about a week later at the same hour of the day you try to find this star, you will notice that it has now become closer to the horizon and is almost hidden in the rays of the evening dawn. This happened because the Sun approached this star. And in a few weeks the star will completely disappear in the sun’s rays and will no longer be visible in the evenings. When another 2-3 weeks have passed, the same star will become visible in the morning, shortly before sunrise, in the eastern part of the sky. Now the Sun, continuing its movement from west to east, will be east of this star.
Such observations show that the Sun not only moves along with all the stars, rising in the east and setting in the west during the day, but also slowly moves among the stars in the opposite direction (i.e. from west to east), moving from constellation to constellation.
Of course, you will not be able to observe the constellation in which the Sun is currently located, since it rises along with the Sun and moves across the sky during the day, that is, when the stars are not visible. The sun with its rays extinguishes the stars not only of the constellation where it is located, but also of all others. Therefore, they cannot be observed.
The path along which the Sun moves among the stars throughout the year is called the ecliptic. It passes through twelve so-called zodiacal constellations, in each of which the Sun appears for approximately one month each year. The zodiac constellations are called: Pisces (March), Aries (April), Taurus (May), Gemini (June), Cancer (July), Leo (August), Virgo (September), Libra (October), Scorpio (November),
Constellations visible at mid-latitudes in the southern half of the sky in spring.
Sagittarius (December), Capricorn (January), Aquarius (February). The months when the Sun is in these constellations are indicated in brackets.
The annual movement of the Sun among the stars is apparent. In fact, the observer himself moves along with the Earth around the Sun. If we observe the stars in the evenings throughout the year, we will discover a gradual change in the starry sky and become familiar with all the constellations that are visible at different times of the year.
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2.1.2. Celestial sphere. Special points of the celestial sphere.
People in ancient times believed that all the stars were located on the celestial sphere, which as a whole revolved around the Earth. Already more than 2,000 years ago, astronomers began to use methods that made it possible to indicate the location of any body on the celestial sphere in relation to other space objects or ground landmarks. The concept of the celestial sphere is convenient to use even now, although we know that this sphere does not really exist.
Celestial sphere -an imaginary spherical surface of an arbitrary radius, in the center of which the observer’s eye is located, and onto which we project the position of the celestial bodies.
The concept of the celestial sphere is used for angular measurements in the sky, for the convenience of reasoning about the simplest visible celestial phenomena, for various calculations, for example, calculating the time of sunrise and sunset.
Let's build a celestial sphere and draw a ray from its center towards the star A(Fig. 1.1).
Where this ray intersects the surface of the sphere, we place a point A 1 representing this star. Star IN will be represented by a dot IN 1 . By repeating a similar operation for all observed stars, we obtain an image of the starry sky on the surface of the sphere - a star globe. It is clear that if the observer is in the center of this imaginary sphere, then for him the direction to the stars themselves and to their images on the sphere will coincide.
- What is the center of the celestial sphere? (Eye of the Observer)
- What is the radius of the celestial sphere? (Arbitrary)
- How do the celestial spheres of two desk neighbors differ? (Center position).
For solving many practical problems, distances to celestial bodies do not play a role; only their visible location in the sky is important. Angular measurements are independent of the radius of the sphere. Therefore, although the celestial sphere does not exist in nature, astronomers use the concept of the Celestial Sphere to study the visible arrangement of luminaries and phenomena that can be observed in the sky over a period of days or many months. The stars, the Sun, the Moon, planets, etc. are projected onto such a sphere, abstracting from the actual distances to the luminaries and considering only the angular distances between them. The distances between stars on the celestial sphere can only be expressed in angular measure. These angular distances are measured by the magnitude of the central angle between the rays directed at one and the other star, or their corresponding arcs on the surface of the sphere.
For an approximate estimate of angular distances in the sky, it is useful to remember the following data: the angular distance between the two extreme stars of the Ursa Major bucket (α and β) is about 5° (Fig. 1.2), and from α Ursa Major to α Ursa Minor (Pole Star) - 5 times more - approximately 25°.
The simplest visual estimates of angular distances can also be carried out using the fingers of an outstretched hand.
We see only two luminaries - the Sun and the Moon - as disks. The angular diameters of these disks are almost the same - about 30" or 0.5°. The angular sizes of planets and stars are much smaller, so we see them simply as luminous points. To the naked eye, an object does not look like a point if its angular sizes exceed 2 -3". This means, in particular, that our eye distinguishes each individual luminous point (star) if the angular distance between them is greater than this value. In other words, we see an object as not a point only if the distance to it exceeds its size by no more than 1700 times.
Plumb line Z, Z' , passing through the eye of the observer (point C), located in the center of the celestial sphere, intersects the celestial sphere at points Z - zenith,Z’ - nadir.
Zenith- this is the highest point above the observer's head.
Nadir -point of the celestial sphere opposite to the zenith.
The plane perpendicular to the plumb line is calledhorizontal plane (or horizon plane).
Mathematical horizoncalled the line of intersection of the celestial sphere with a horizontal plane passing through the center of the celestial sphere.
With the naked eye, you can see about 6,000 stars in the entire sky, but we see only half of them, because the other half of the starry sky is blocked from us by the Earth. Do the stars move across the sky? It turns out that everyone is moving and at the same time. You can easily verify this by observing the starry sky (focusing on certain objects).
Due to its rotation, the appearance of the starry sky changes. Some stars are just emerging from the horizon (rising) in the eastern part, others at this time are high above your head, and still others are already hiding behind the horizon in the western side (setting). At the same time, it seems to us that the starry sky rotates as a single whole. Now everyone knows well that The rotation of the sky is an apparent phenomenon caused by the rotation of the Earth.
A picture of what happens to the starry sky as a result of the daily rotation of the Earth can be captured with a camera.
In the resulting image, each star left its mark in the form of a circular arc (Fig. 2.3). But there is also a star whose movement throughout the night is almost imperceptible. This star was called Polaris. Over the course of a day, it describes a circle of small radius and is always visible at almost the same height above the horizon in the northern side of the sky. The common center of all concentric star trails is located in the sky near the North Star. This point to which the Earth's rotation axis is directed is called north celestial pole. The arc described by the North Star has the smallest radius. But this arc and all the others - regardless of their radius and curvature - form the same part of the circle. If it were possible to photograph the paths of stars in the sky over a whole day, then the photograph would turn out to be complete circles - 360°. After all, a day is the period of a complete revolution of the Earth around its axis. In an hour, the Earth will rotate 1/24 of a circle, i.e. 15°. Consequently, the length of the arc that the star will describe during this time will be 15°, and in half an hour - 7.5°.
During the course of a day, the stars describe larger circles, the farther they are from the North Star.
The axis of daily rotation of the celestial sphere is calledaxis mundi (RR").
The points of intersection of the celestial sphere with the axis of the world are calledpoles of the world(dot R - north celestial pole, point R" - south celestial pole).
The North Star is located near the north pole of the world. When we look at the North Star, or more precisely, at a fixed point next to it - the north pole of the world, the direction of our gaze coincides with the axis of the world. The south celestial pole is located in the southern hemisphere of the celestial sphere.
Plane EAW.Q., perpendicular to the axis of the world PP" and passing through the center of the celestial sphere is calledplane of the celestial equator, and the line of its intersection with the celestial sphere iscelestial equator.
Celestial equator – a line of a circle obtained from the intersection of the celestial sphere with a plane passing through the center of the celestial sphere perpendicular to the axis of the world.
The celestial equator divides the celestial sphere into two hemispheres: northern and southern.
The axis of the world, the poles of the world and the celestial equator are similar to the axis, poles and equator of the Earth, since the listed names are associated with the apparent rotation of the celestial sphere, and it is a consequence of the actual rotation of the globe.
Plane passing through the zenith pointZ , center WITH celestial sphere and pole R the world is calledplane of the celestial meridian, and the line of its intersection with the celestial sphere formscelestial meridian line.
Celestial meridian – a great circle of the celestial sphere passing through the zenith Z, the celestial pole P, the south celestial pole P, nadir Z"
In any place on Earth, the plane of the celestial meridian coincides with the plane of the geographical meridian of this place.
Noon Line N.S. - this is the line of intersection of the meridian and horizon planes. N – north point, S – south point
It is so named because at midday shadows from vertical objects fall in this direction.
- What is the period of rotation of the celestial sphere? (Equal to the period of rotation of the Earth - 1 day).
- In what direction does the visible (apparent) rotation of the celestial sphere occur? (Opposite to the direction of rotation of the Earth).
- What can be said about the relative position of the axis of rotation of the celestial sphere and the earth's axis? (The axis of the celestial sphere and the earth's axis will coincide).
- Do all points of the celestial sphere participate in the apparent rotation of the celestial sphere? (Points lying on the axis are at rest).
The Earth moves in orbit around the Sun. The Earth's rotation axis is inclined to the orbital plane at an angle of 66.5°. Due to the action of gravitational forces from the Moon and the Sun, the Earth's rotation axis shifts, while the inclination of the axis to the plane of the Earth's orbit remains constant. The Earth's axis seems to slide along the surface of the cone. (the same thing happens with the axis of an ordinary top at the end of rotation).
This phenomenon was discovered back in 125 BC. e. by the Greek astronomer Hipparchus and named precession.
The earth's axis completes one revolution in 25,776 years - this period is called the Platonic year. Now near the P - north pole of the world there is the North Star - α Ursa Minor. The polar star is the star that is currently located near the North Pole of the world. In our time, since about 1100, such a star is Alpha Ursa Minor - Kinosura. Previously, the title of Polaris was alternately assigned to π, η and τ Hercules, the stars Thuban and Kohab. The Romans did not have the North Star at all, and Kohab and Kinosura (α Ursa Minor) were called Guardians.
At the beginning of our chronology, the celestial pole was near α Draco - 2000 years ago. In 2100, the celestial pole will be only 28" from the North Star - now it is 44". In 3200 the constellation Cepheus will become polar. In 14000 Vega (α Lyrae) will be polar.
How to find the North Star in the sky?
To find the North Star, you need to mentally draw a straight line through the stars of Ursa Major (the first 2 stars of the “bucket”) and count 5 distances between these stars along it. In this place, next to the straight line, we will see a star almost identical in brightness to the stars of the “bucket” - this is the North Star.
In the constellation, which is often called the Little Dipper, the North Star is the brightest. But just like most of the stars in the Ursa Major bucket, Polaris is a star of second magnitude.
Summer (summer-autumn) triangle = star Vega (α Lyrae, 25.3 light years), star Deneb (α Cygnus, 3230 light years), star Altair (α Orlae, 16.8 light years)
Imagine that you are spinning, as you did in childhood. And on the button of your shirt sits a microscopic man. What will he see and feel?
It will seem to him that the entire furnishings of the room revolves around him: chairs, a table, a TV, paintings on the walls, and the relative position of all these objects will remain unchanged...
And only two points, one point at the top, on the ceiling, and the other point at the bottom, on the floor, will remain motionless.
And if your beloved cat suddenly goes somewhere about its business, then its location in relation to the home environment will change.
And the most amazing thing. It will seem to a microscopic man that he is the one who is motionless, and everything revolves around him, because people cannot always sense their own movement. For example, it happens that we look out the window of a carriage and don’t know whether it’s the neighboring train that has left, or our train that has moved slowly and smoothly. Another example: when we are sitting on an airplane, we do not feel that we are flying at a speed of a hundred meters per second.
What is all this for?
And what has been said can be repeated verbatim, if we accept that we are microscopic people living on the Earth rotating around its axis. The furnishings of the room are like stars, a cat is the Moon, two fixed points are the poles of the world.
We live on the Earth rotating around its axis, and it seems to us that the entire sky revolves around us, making a full revolution in about a day. Therefore, such rotation is called the daily movement of the sky.
The diurnal movement is visible to the naked eye: after a couple of hours, the turn of the sky literally catches the eye.
And here is a photograph of the sky taken with a fixed camera, exposure time one hour. Almost all the stars turned out to be in the form of lines, because their position in the sky changed during the photography.
The only star that remains motionless and appears as a dot in the photograph is the North Star. This is far from the brightest star, which is remarkable in that it is very close to the North Pole of the world - that point in the sky that remains motionless during the daily movement of the sky.
The diametrically opposite point in the sky, the South Pole of the world, also remains motionless. The south pole of the world is not visible to us, residents of the northern hemisphere of the Earth, it is always below the horizon. In the southern hemisphere of the Earth, on the contrary, only the South Pole of the world is visible.
About distances in the sky.
You can’t put a ruler to the sky, you can’t measure distances in meters or centimeters. You can only measure angles between any two directions.
For example, the angles between any two stars, or the angle between the centers of the disks of the Sun and Moon, etc.
In particular, the poles of the world are diametrically opposite points, so the angle between them is 180°.
Points 90° away from both the North and South Pole of the world constitute the celestial equator. Similarly, the points of the earth's equator are equally distant from the earth's poles.
The celestial equator divides the sky into two halves. That half of the sky that contains the North Pole of the world is called the northern hemisphere of the sky, and the other half that contains the South Pole of the world is called the southern hemisphere. And here, too, there is a complete analogy with the Earth.
About constellations and star maps.
Now remember - you were spinning, but the furnishings in the room did not change their relative positions.
In the same way, the stars maintain their relative positions during the daily rotation of the sky, forming characteristic patterns. Such drawings are colloquially called constellations.
For example, in the upper right part of the photo, the constellation Orion is visible near the horizon.
The wild imagination of people saw a person in a group of bright stars from the constellation Orion. In Greek mythology, Orion was a famous hunter who could defeat any game.
In the past, the starry sky was depicted in the form of drawings with pictures, like the one depicting Orion, the hunter, and Taurus, the game.
Nowadays, they use star maps, which differ from photographs or sky drawings in that
Maps have coordinate lines, i.e. objects are plotted on the map according to their celestial coordinates. Similarly, geographic maps also have coordinate lines (parallels and meridians), and objects are plotted on the map according to their coordinates - geographic latitude and longitude.
Celestial objects are depicted using symbols, so visually the view of the starry sky and the map are noticeably different (just as the view of some area from an airplane window is visually different from a map of the same area).
On the map, the stars are depicted as black circles. The larger the circle, the brighter the star.
A characteristic detail in the constellation Orion is three stars located side by side on the same straight line.
If you look to the left along this straight line, you can see the brightest star in the sky - Sirius, otherwise it is called α (alpha) Canis Major, - Canis Major in Latin. Both in the picture and on the map Sirius is depicted in the lower left corner.
The thick blue line is part of the celestial equator. The fainter blue lines parallel and perpendicular to the celestial equator are coordinate lines.
The dotted lines are the boundaries of the constellations. A constellation is not at all a group of stars, as many people think.
A constellation is an area of the sky within certain boundaries established by international agreement. There are a total of 88 constellations in the sky. That's all. - There is no more room in the sky!
Now remember: the microscopic man saw that the cat, which had gone about its business, was moving in relation to household items.
Likewise, the Moon orbits the Earth and therefore moves quite quickly across the sky relative to the stars. You can see this for yourself. - Within a day, the Moon will be visible against the background of other stars.
And in general, all the celestial bodies of the Solar System move across the sky, changing their position among the stars.
