Do the equatorial coordinates of a star change? Practical work with a moving star map

Note:

1. (Alpha Canis Majoris; αCMa, Sirius). The brightest star in the constellation Canis Major and the brightest star in the sky. It is a visual binary star with an orbital period of 50 years, the main component (A) being an A star and the second component (B, Pup) an 8th magnitude white dwarf. Sirius B was first discovered optically in 1862, and its type was determined from its spectrum in 1925. Sirius is 8.7 light years away from us and ranks seventh in terms of proximity to the Solar System. The name is inherited from the ancient Greeks and means “scorching,” which emphasizes the brilliance of the star. In connection with the name of the constellation to which Sirius belongs, it is also called the “Dog Star”. The third star, a brown dwarf, closer to (A) than component (B), was discovered by French astronomers in 1995.
2. (Alpha Bootes, αBoo, Arcturus). The brightest star in the constellation Bootes, an orange giant K-star, is the fourth brightest star in the sky. Double, variable. The name is of Greek origin and means “bear keeper.” Arcturus was the first star to be seen during the day using a telescope by the French astronomer and astrologer Morin in 1635.
3. (Alpha Lyrae; α Lyr, Vega). The brightest star in the constellation Lyra and the fifth brightest star in the sky. This is an A-star. In 2005, the Spitzer Space Telescope captured infrared images of Vega and the dust surrounding the star. A planetary system is formed around a star.
4. (Alpha Aurigae; α Aur, Chapel). The brightest star in the constellation Auriga, a spectroscopic double star in which the main component is a giant G-star. Her name is of Latin origin and means “little goat.”
5. (Beta Orionis; β Ori, Rigel). The brightest star in the constellation Orion. It is designated by the Greek letter Beta, although it is slightly brighter than Betelgeuse, which is designated Alpha Orionis. Rigel is a supergiant B star with a 7th magnitude companion. The name, which is of Arabic origin, means "giant's foot."
6. (Alpha Canis Minor; αCMi, Procyon). The brightest star in the constellation Canis Minor. Procyon ranks fifth in brightness among all stars. In 1896, J. M. Scheberl discovered that Procyon is a binary system. The main companion is a normal F star, and the faint companion is an 11th magnitude white dwarf. The system's circulation period is 41 years. The name Procyon is of Greek origin and means "before the dog" (a reminder that the star rises before the "Dog Star", i.e. Sirius).
7. (Alpha Eagle; α Aql, Altair). The brightest star in the constellation Aquila. The Arabic word "altair" means "flying eagle". Altair - A-star. It is one of the closest among the brightest stars (located at a distance of 17 light years).
8. (Alpha Orionis; α Ori, Betelgeuse). A red supergiant M star, one of the largest known stars. Using point interferometry and other interference methods, it was possible to measure its diameter, which turned out to be approximately 1000 times the diameter of the Sun. The presence of large bright “starspots” was also discovered. Observations in the ultraviolet using the Hubble Space Telescope have shown that Betelgeuse is surrounded by a vast chromosphere with a mass of approximately twenty solar masses. Variable. The brightness varies irregularly between magnitudes 0.4 and 0.9 with a period of about five years. It is noteworthy that during the observation period from 1993 to 2009, the diameter of the star decreased by 15%, from 5.5 astronomical units to approximately 4.7, and astronomers cannot yet explain why this is due. However, the brightness of the star did not change any noticeably during this time.
9. (Alpha Taurus; α Tau, Aldebaran). The brightest star in the constellation Taurus. The Arabic name means “next” (i.e. following the Pleiades). Aldebaran is a giant K star. Variable. Although in the sky the star appears to be part of the Hyades cluster, it is not actually a member of it, being twice as close to Earth. In 1997, it was reported about the possible existence of a satellite - a large planet (or a small brown dwarf), with a mass equal to 11 Jupiter masses at a distance of 1.35 AU. The unmanned spacecraft Pioneer 10 is heading towards Aldebaran. If nothing happens to it along the way, it will reach the region of the star in about 2 million years.
10. (Alpha Scorpio; α Sco, Antares). The brightest star in the constellation Scorpio. Red supergiant, M-star, variable, binary The name is of Greek origin and means “competitor of Mars,” which recalls the remarkable color of this star. Antares is a semi-regular variable star whose brightness varies between magnitudes 0.9 and 1.1 with a five-year period. It has a blue companion star of 6th magnitude, only 3 arc seconds distant. Antares B was discovered during one of these occultations on April 13, 1819. The satellite's orbital period is 878 years.
11. (Alpha Virgo; αVir, Spica). The brightest star in the constellation Virgo. It is an eclipsing binary, variable, whose brightness varies by about 0.1 magnitude with a period of 4.014 days. The main component is a blue-white B star with a mass of about eleven solar masses. The name means "cob of corn".
12. (Beta Gemini; β Gem, Pollux). The brightest star in the constellation Gemini, although its designation is Beta rather than Alpha. It seems unlikely that Pollux has become brighter since the time of Bayer (1572-1625). Pollux is an orange giant K star. In classical mythology, the twins Castor and Pollux were the sons of Leda. In 2006, an exoplanet was discovered near the star.
13. (Alpha Southern Pisces; α PsA,
14. (Epsilon Canis Majoris; εCMa, Adara). The second brightest star (after Sirius) in the constellation Canis Major, a giant B star. Has a companion star of 7.5 m. The Arabic name of the star means “virgin”. Approximately 4.7 million years ago, the distance from ε Canis Majoris to Earth was 34 light years, and the star was the brightest in the sky, its brilliance was equal to −4.0 m
15. (Alpha Gemini; α Gem, Castor). The second brightest in the constellation Gemini after Pollux. Its naked-eye magnitude is estimated to be 1.6, but this is the combined brightness of a multiple system consisting of at least six components. There are two A stars with magnitudes 2.0 and 2.9, forming a close visual pair, each of which is a spectroscopic binary, and a more distant red star of magnitude 9, which is an eclipsing binary.
16. (Gamma Orionis; γ Ori, Bellatrix). Giant, B-star, variable, double. The name is of Latin origin and means “warrior woman.” One of the 57 navigational stars of antiquity
17. (Beta Taurus; β Tau, Nat). The second brightest in the constellation Taurus, lying on the tip of one of the bull's horns. The name comes from the Arabic expression "goring with horns." This star on ancient maps depicted the right leg of a human figure in the constellation Auriga and had another designation, Gamma Auriga. Elnat is a B-star.
18. (Epsilon Orionis; ε Ori, Alnilam). One of the three bright stars that form Orion's belt. The Arabic name translates as "string of pearls". Alnilam - supergiant, B-star, variable
19. (Zeta Orionis; ζ Ori, Alnitak). One of the three bright stars that form Orion's belt. The Arabic name translates as "belt". Alnitak is a supergiant, O-star, triple star.
20. (Epsilon Ursa Major; ε UMa, Aliot). The brightest star in the constellation Ursa Major. The Greek letters in this case are assigned to the stars in order of their position, not brightness. Alioth is an A star, possibly having a planet 15 times more massive than Jupiter.
21. (Alpha Ursa Major; αUMa, Dubhe). One of two stars (the other is Merak) of the Big Dipper in Ursa Major, called the Indexes. Giant, K-star, variable. The 5th magnitude companion orbits it every 44 years. Dubhe, literally "bear", is a shortened version of the Arabic name meaning "back of the larger bear".
22. (Alpha Persei;α Per, Mirfak). The brightest star in the constellation Perseus. Yellow supergiant, F-star, variable. The name, of Arabic origin, means "elbow".
23. (This Ursa Major; ηUMa, Benetnash). The star is located at the end of the “tail”. B-star, variable. The Arabic name means “leader of mourners” (for the Arabs, the constellation was seen as a hearse, not a bear).
24. (Beta Canis Majoris; βCMa, Mirzam). The second brightest in the constellation Canis Major. A giant B star, a variable, is the prototype of a class of weakly variable stars such as Beta Canis Majoris. Its brightness changes every six hours by a few hundredths of a magnitude. Such a low level of variability is not detectable with the naked eye.
25. (Alpha Hydra; αHya, Alphard). The brightest star in the constellation Hydra. The name is of Arabic origin and means “solitary snake.” Alphard - K-star, variable, triple.
26. (Alpha Ursa Minor; αUMi, Polar). The brightest star in the constellation Ursa Minor, located near the north celestial pole (at a distance of less than one degree). Polaris is the closest pulsating variable star of the Delta Cepheus type to Earth with a period of 3.97 days. But Polar is a very non-standard Cepheid: its pulsations fade over a period of about tens of years: in 1900 the change in brightness was ±8%, and in 2005 - approximately 2%. In addition, during this time the star became on average 15% brighter.

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The purpose of the lesson: introduce students to stellar coordinates, instill the skills of determining these coordinates on a model of the celestial sphere.

Equipment: video projector, model of the celestial sphere

During the classes

Teacher: Since time immemorial, people have identified separate groups of bright stars in the starry sky, united them into constellations, giving them names that reflected the way of life and the peculiarities of their thinking. This is what ancient Chinese, Babylonian, and Egyptian astronomers did. Many of the constellation names we use today come from ancient Greece, where they evolved over centuries.

Table 1 Chronicle of names

At the Congress of the International Astronomical Union in 1922, the number of constellations was reduced to 88. At the same time, the current boundaries between them were established.

It deserves special mention. That the proximity of stars in constellations is apparent, is how an observer from Earth sees them. In fact, the stars lag behind each other at great distances, and for us their visibility is, as it were, projected onto celestial sphere- an imaginary transparent ball, in the center of which is the Earth (observer), onto the surface of which all the luminaries are projected as the observer sees them at a certain moment in time from a certain point in space. Presentation. Slide 1

Moreover, the stars in the constellations are different; they differ in apparent size and light. The brightest stars in the constellations are designated by letters of the Greek alphabet in descending order (a, b, g, d, e, etc.) of brightness.

This tradition was introduced by Alessandro Piccolomini (1508–1578), and consolidated by Johann Bayer (1572–1625).

Then John Flamsteed (1646–1719) within each constellation designated the stars by serial number (for example, the star 61 Cygnus). Stars with variable brightness are designated by Latin letters: R, S, Z, RR, RZ, AA.

Now we will look at how the location of the luminaries in the sky is determined.

Let's imagine the sky in the form of a giant globe of arbitrary radius, in the center of which the observer is located.

However, the fact that some luminaries are located closer to us, while others are further away, is not visible to the eye. Therefore, let us assume that all stars are at the same distance from the observer - on the surface celestial sphere. Presentation. Slide 1

Since the stars change their position during the day, we can conclude about the daily rotation of the celestial sphere (this is explained by the rotation of the Earth around its axis). The celestial sphere rotates around a certain axis PP` from east to west. The axis of apparent rotation of the sphere is the axis of the world. It coincides with the earth's axis or is parallel to it. The axis of the world intersects the celestial sphere at points P – north celestial pole and P`- south celestial pole. The North Star (a Ursa Minor) is located near the north pole of the world. Using a plumb line, we determine the vertical and depict it in the drawing. Presentation. Slide 1

This straight line ZZ` is called plumb line. Z – zenith, Z`- nadir. Through point O - the intersection of the plumb line and the axis of the world - we draw a straight line perpendicular to ZZ`. This is NS - noon line(N- north, S – south). Objects illuminated by the Sun at noon cast a shadow in the direction along this line.

Two mutually perpendicular planes intersect along the noon line. A plane perpendicular to a plumb line that intersects the celestial sphere in a great circle is true horizon. Presentation. Slide 1

The plane perpendicular to the true horizon passing through the points Z and Z` is called celestial meridian.

We have drawn all the necessary planes, now let's introduce another concept. Let us arbitrarily place a star on the surface of the celestial sphere M, draw through points Z and Z` and M big semicircle. This - height circle or vertical

The instantaneous position of the star relative to the horizon and the celestial meridian is determined by two coordinates: height(h) and azimuth(A). These coordinates are called horizontal.

The altitude of the luminary is the angular distance from the horizon, measured in degrees, minutes, arc seconds ranging from 0° to 90°. More height replaced by an equivalent coordinate – z – zenith distance.

The second coordinate in the horizontal system A is the angular distance of the vertical of the luminary from the point of south. Defined in degrees minutes and seconds from 0° to 360°.

Notice how the horizontal coordinates change. Light M during the day describes a daily parallel on the celestial sphere - this is a circle of the celestial sphere, the plane of which is perpendicular axis mundi.

<Отработка навыка определения горизонтальных координат на небесной сфере. Самостоятельная работа учащихся>

When a star moves along the daily parallel, the highest point of ascent is called upper climax. Moving under the horizon, the luminary will end up at a point, which will be a point lower climax. Presentation. Slide 1

If we consider the path of the star we have chosen, we can see that it is rising and setting, but there are non-setting and non-rising luminaries. (Here - relative to the true horizon.)

Let's consider the change in the appearance of the starry sky throughout the year. These changes are not as noticeable for most stars, but they do occur. There is a star whose position changes quite dramatically, this is the Sun.

If we draw a plane through the center of the celestial sphere and perpendicular to the axis of the world PP`, then this plane will intersect the celestial sphere in a great circle. This circle is called celestial equator. Presentation. Slide 2

This celestial equator intersects with the true horizon at two points: east (E) and west (W). All daily parallels are located parallel to the equator.

Now let's draw a circle through the poles of the world and the observed star. The result is a circle - a circle of declination. The angular distance of the luminary from the plane of the celestial equator, measured along the declination circle, is called the declination of the luminary (d). Declination is expressed in degrees, minutes and seconds. Since the celestial equator divides the celestial sphere into two hemispheres (northern and southern), the declination of stars in the northern hemisphere can vary from 0° to 90°, and in the southern hemisphere - from 0° to -90°.

The declination of the luminary is one of the so-called equatorial coordinates.

The second coordinate in this system is right ascension (a). It is similar to geographic longitude. Right ascension is counted from vernal equinox points (g). The Sun appears at the vernal equinox on March 21st. Right ascension is measured along the celestial equator in the direction opposite to the daily rotation of the celestial sphere. Presentation. Slide 2. Right ascension is expressed in hours, minutes and seconds of time (from 0 to 24 hours) or in degrees, minutes and seconds of arc (from 0° to 360°). Since the position of stars relative to the equator does not change when the celestial sphere moves, equatorial coordinates are used to create maps, atlases and catalogs.

Since ancient times it was noticed that the Sun moves among the stars and describes a full circle in one year. The ancient Greeks called this circle ecliptic, which has been preserved in astronomy to this day. Ecliptic inclined to the plane of the celestial equator at an angle of 23°27` and intersects with the celestial equator at two points: the vernal equinox (g) and the autumn equinox (W). The Sun travels the entire ecliptic in a year; it travels 1° per day.

The constellations through which the ecliptic passes are called zodiac. Every month the Sun moves from one constellation to another. It is virtually impossible to see the constellation in which the Sun is located at noon, since it obscures the light of the stars. Therefore, in practice, at midnight we observe the zodiac constellation, which is the highest above the horizon, and from it we determine the constellation where the Sun is located at noon (Figure No. 14 of the Astronomy 11 textbook).

We should not forget that the annual movement of the Sun along the ecliptic is a reflection of the actual movement of the Earth around the Sun.

Let us consider the position of the Sun on a model of the celestial sphere and determine its coordinates relative to the celestial equator (repetition).

<Отработка навыка определения экваториальных координат на небесной сфере. Самостоятельная работа учащихся>

Homework.

1. Know the contents of paragraph 116 of the Physics-11 textbook
2. Know the contents of paragraphs 3, 4 of the textbook Astronomy -11
3. Prepare material on the topic “Zodiac constellations”

Literature.

1. E.P. Levitan Astronomy 11th grade – Enlightenment, 2004
2. G.Ya. Myakishev and others. Physics 11th grade - Enlightenment, 2010
3. Encyclopedia for children Astronomy - ROSMEN, 2000

Astronomy is a whole world full of beautiful images. This amazing science helps to find answers to the most important questions of our existence: learn about the structure of the Universe and its past, about the Solar system, about how the Earth rotates, and much more. There is a special connection between astronomy and mathematics, because astronomical predictions are the result of rigorous calculations. In fact, many problems in astronomy became possible to solve thanks to the development of new branches of mathematics.

From this book, the reader will learn about how the position of celestial bodies and the distance between them is measured, as well as about astronomical phenomena during which space objects occupy a special position in space.

If the well, like all normal wells, was directed towards the center of the Earth, its latitude and longitude did not change. The angles that determine Alice's position in space remained unchanged, only her distance to the center of the Earth changed. So Alice didn't have to worry.

Option one: altitude and azimuth

The most understandable way to determine coordinates on the celestial sphere is to indicate the angle that determines the height of the star above the horizon, and the angle between the north-south straight line and the projection of the star onto the horizon line - azimuth (see the following figure).

HOW TO MEASURE ANGLES MANUALLY

A device called a theodolite is used to measure the altitude and azimuth of a star.

However, there is a very simple, although not very accurate, way to measure angles manually. If we extend our hand in front of us, the palm will indicate an interval of 20°, the fist - 10°, the thumb - 2°, the little finger -1°. This method can be used by both adults and children, since the size of a person’s palm increases in proportion to the length of his arm.

Option two, more convenient: declination and hour angle

Determining the position of a star using azimuth and altitude is not difficult, but this method has a serious drawback: the coordinates are tied to the point at which the observer is located, so the same star, when observed from Paris and Lisbon, will have different coordinates, since the horizon lines in these cities will be located differently. Consequently, astronomers will not be able to use this data to exchange information about their observations. Therefore, there is another way to determine the position of the stars. It uses coordinates reminiscent of the latitude and longitude of the earth's surface, which can be used by astronomers anywhere on the globe. This intuitive method takes into account the position of the Earth's rotation axis and assumes that the celestial sphere rotates around us (for this reason, the Earth's rotation axis was called the axis mundi in Antiquity). In reality, of course, the opposite is true: although it seems to us that the sky is rotating, in fact it is the Earth that is rotating from west to east.

Let us consider a plane cutting the celestial sphere perpendicular to the axis of rotation passing through the center of the Earth and the celestial sphere. This plane will intersect the earth's surface along a great circle - the earth's equator, and also the celestial sphere - along its great circle, which is called the celestial equator. The second analogy with earthly parallels and meridians would be the celestial meridian, passing through two poles and located in a plane perpendicular to the equator. Since all celestial meridians, like terrestrial ones, are equal, the prime meridian can be chosen arbitrarily. Let us choose as the zero meridian the celestial meridian passing through the point at which the Sun is located on the day of the vernal equinox. The position of any star and celestial body is determined by two angles: declination and right ascension, as shown in the following figure. Declination is the angle between the equator and the star, measured along the meridian of a place (from 0 to 90° or from 0 to -90°). Right ascension is the angle between the vernal equinox and the meridian of the star, measured along the celestial equator. Sometimes, instead of right ascension, the hour angle, or the angle that determines the position of the celestial body relative to the celestial meridian of the point at which the observer is located, is used.

The advantage of the second equatorial coordinate system (declination and right ascension) is obvious: these coordinates will be unchanged regardless of the position of the observer. In addition, they take into account the rotation of the Earth, which makes it possible to correct the distortions it introduces. As we have already said, the apparent rotation of the celestial sphere is caused by the rotation of the Earth. A similar effect occurs when we are sitting on a train and see another train moving next to us: if you do not look at the platform, you cannot determine which train has actually started moving. We need a starting point. But if instead of two trains we consider the Earth and the celestial sphere, finding an additional reference point will not be so easy.

In 1851 a Frenchman Jean Bernard Leon Foucault (1819–1868) conducted an experiment demonstrating the motion of our planet relative to the celestial sphere.

He suspended a load weighing 28 kilograms on a 67-meter-long wire under the dome of the Parisian Pantheon. The oscillations of the Foucault pendulum lasted 6 hours, the oscillation period was 16.5 seconds, the pendulum deflection was 11° per hour. In other words, over time, the plane of oscillation of the pendulum shifted relative to the building. It is known that pendulums always move in the same plane (to verify this, just hang a bunch of keys on a rope and watch its vibrations). Thus, the observed deviation could be caused by only one reason: the building itself, and therefore the entire Earth, rotated around the plane of oscillation of the pendulum. This experiment became the first objective evidence of the rotation of the Earth, and Foucault pendulums were installed in many cities.

The Earth, which appears to be motionless, rotates not only on its own axis, making a complete revolution in 24 hours (equivalent to a speed of about 1600 km/h, that is, 0.5 km/s if we are at the equator), but also around the Sun , making a full revolution in 365.2522 days (with an average speed of approximately 30 km/s, that is, 108000 km/h). Moreover, the Sun rotates relative to the center of our galaxy, completing a full revolution every 200 million years and moving at a speed of 250 km/s (900,000 km/h). But that’s not all: our galaxy is moving away from the rest. Thus, the movement of the Earth is more like a dizzying carousel in an amusement park: we spin around ourselves, move through space and describe the spiral at breakneck speed. At the same time, it seems to us that we are standing still!

Although other coordinates are used in astronomy, the systems we have described are the most popular. It remains to answer the last question: how to convert coordinates from one system to another? The interested reader will find a description of all the necessary transformations in the application.

MODEL OF THE FOUCAULT EXPERIMENT

We invite the reader to conduct a simple experiment. Let's take a round box and glue a sheet of thick cardboard or plywood onto it, onto which we will attach a small frame in the shape of a football goal, as shown in the figure. Let's place a doll in the corner of the sheet, which will play the role of an observer. We tie a thread to the horizontal bar of the frame, on which we attach the sinker.

Let's move the resulting pendulum to the side and release it. The pendulum will oscillate parallel to one of the walls of the room in which we are located. If we begin to smoothly rotate the sheet of plywood together with the round box, we will see that the frame and the doll will begin to move relative to the wall of the room, but the plane of oscillation of the pendulum will still be parallel to the wall.

If we imagine ourselves as a doll, we will see that the pendulum moves relative to the floor, but at the same time we will not be able to feel the movement of the box and the frame on which it is attached. Similarly, when we observe a pendulum in a museum, it seems to us that the plane of its oscillations is shifting, but in fact we ourselves are shifting along with the museum building and the entire Earth.

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To make a star map depicting constellations on a plane, you need to know the coordinates of the stars. The coordinates of stars relative to the horizon, for example altitude, although visual, are unsuitable for making maps, since they change all the time. It is necessary to use a coordinate system that rotates with the starry sky. It is called the equatorial system. In it, one coordinate is the angular distance of the luminary from the celestial equator, called declination (Fig. 19). It varies within ±90° and is considered positive north of the equator and negative south. Declination is similar to geographic latitude.

The second coordinate is similar to geographic longitude and is called right ascension a.

Rice. 18. Daily paths of the Sun above the horizon at different times of the year during observations: a - in mid-latitudes; b - at the Earth's equator.

Rice. 19. Equatorial coordinates.

Rice. 20. The height of the luminary at the upper culmination.

The right ascension of the luminary M is measured by the angle between the planes of the great circle drawn through the poles of the world and the given luminary and the great circle passing through the poles of the world and the point of the vernal equinox (Fig. 19). This angle is measured from the vernal equinox T counterclockwise when viewed from the north pole. It varies from 0 to 360° and is called right ascension because the stars located on the celestial equator rise in order of increasing right ascension. In the same order they culminate one after another. Therefore, a is usually expressed not in angular measure, but in time, and it is assumed that the sky rotates by 15°, and by 1° in 4 minutes. Therefore, right ascension is 90°, otherwise it will be 6 hours, and 7 hours 18 minutes. In units of time, right ascensions are written along the edges of the star chart.

There are also star globes, where the stars are depicted on the spherical surface of the globe.

On one map, only part of the starry sky can be depicted without distortion. It is difficult for beginners to use such a map, because they do not know which constellations are visible at a given time and how they are located relative to the horizon. A moving star map is more convenient. The idea of ​​its device is simple. Superimposed on the map is a circle with a cutout representing the horizon line. The horizon cutout is eccentric, and when you rotate the overlay circle in the cutout, constellations that are above the horizon at different times will be visible. How to use such a card is described in Appendix VII.

(see scan)

2. The height of the luminaries at the culmination.

Let's find the relationship between the height of the luminary M at the upper culmination, its declination 6 and the latitude of the area

Figure 20 shows the plumb line of the celestial axis and the projection of the celestial equator and the horizon line (noon line) onto the plane of the celestial meridian. The angle between the noon line and the celestial axis is equal, as we know, to the latitude of the area. Obviously, the inclination of the plane of the celestial equator to the horizon, measured by the angle, is equal to 90° - (Fig. 20). The star M with declination 6, culminating south of the zenith, has a height of

From this formula it can be seen that geographic latitude can be determined by measuring the altitude of any star with a known declination of 6 at its upper culmination. It should be taken into account that if the star at the moment of culmination is located south of the equator, then its declination is negative.

(see scan)

3. Exact time.

For measuring short periods of time in astronomy, the basic unit is the average length of the solar day, that is, the average period of time between the two upper (or lower) culminations of the center of the Sun. The average value must be used because the length of the sunny day fluctuates slightly throughout the year. This is due to the fact that the Earth revolves around the Sun not in a circle, but in an ellipse, and the speed of its movement changes slightly. This causes slight irregularities in the apparent movement of the Sun along the ecliptic throughout the year.

The moment of the upper culmination of the center of the Sun, as we have already said, is called true noon. But to check the clock, to determine the exact time, there is no need to mark on it exactly the moment of the culmination of the Sun. It is more convenient and accurate to mark the moments of the culmination of stars, since the difference between the moments of the culmination of any star and the Sun is precisely known for any time. Therefore, to determine the exact time, using special optical instruments, they mark the moments of the culminations of the stars and use them to check the correctness of the clock that “stores” time. The time determined in this way would be absolutely accurate if the observed rotation of the sky occurred with a strictly constant angular velocity. However, it turned out that the speed of the Earth’s rotation around its axis, and therefore the apparent rotation of the celestial

sphere, experiences very small changes over time. Therefore, to “save” exact time, special atomic clocks are now used, the course of which is controlled by oscillatory processes in atoms that occur at a constant frequency. The clocks of individual observatories are checked against atomic time signals. Comparing time determined from atomic clocks and the apparent motion of stars makes it possible to study the irregularities of the Earth's rotation.

Determining the exact time, storing it and transmitting it by radio to the entire population is the task of the exact time service, which exists in many countries.

Precise time signals via radio are received by navigators of the navy and air force, and many scientific and industrial organizations that need to know the exact time. Knowing the exact time is necessary, in particular, to determine the geographical longitudes of different points on the earth's surface.

4. Counting time. Determination of geographic longitude. Calendar.

From the course of physical geography of the USSR, you know the concepts of local, zone and maternity time, and also that the difference in geographical longitude of two points is determined by the difference in the local time of these points. This problem is solved by astronomical methods using star observations. Based on determining the exact coordinates of individual points, the earth's surface is mapped.

To count large periods of time, people since ancient times have used the duration of either a lunar month or a solar year, i.e., the duration of the Sun's revolution along the ecliptic. The year determines the frequency of seasonal changes. A solar year lasts 365 solar days, 5 hours 48 minutes 46 seconds. It is practically incommensurate with the day and with the length of the lunar month - the period of change of lunar phases (about 29.5 days). This is the difficulty of creating a simple and convenient calendar. Over the centuries-old history of mankind, many different calendar systems have been created and used. But all of them can be divided into three types: solar, lunar and lunisolar. Southern pastoral peoples usually used lunar months. A year consisting of 12 lunar months contained 355 solar days. To coordinate the calculation of time by the Moon and the Sun, it was necessary to establish either 12 or 13 months in the year and insert additional days into the year. The solar calendar, which was used in Ancient Egypt, was simpler and more convenient. Currently, most countries in the world also adopt a solar calendar, but a more advanced one, called the Gregorian calendar, which is discussed below.

When compiling a calendar, it is necessary to take into account that the duration of the calendar year should be as close as possible to the duration of the Sun's revolution along the ecliptic and that the calendar year should contain a whole number of solar days, since it is inconvenient to start the year at different times of the day.

These conditions were satisfied by the calendar developed

by the Alexandrian astronomer Sosigenes and introduced in 46 BC. e. in Rome by Julius Caesar. Subsequently, as you know from the course of physical geography, it received the name Julian or old style. In this calendar, the years are counted three times in a row for 365 days and are called simple, the year following them is 366 days. It's called a leap year. Leap years in the Julian calendar are those years whose numbers are divisible by 4 without a remainder.

The average length of the year according to this calendar is 365 days 6 hours, i.e. it is approximately 11 minutes longer than the true one. Because of this, the old style lagged behind the actual flow of time by about 3 days every 400 years.

In the Gregorian calendar (new style), introduced in the USSR in 1918 and even earlier adopted in most countries, years ending in two zeros, with the exception of 1600, 2000, 2400, etc. (i.e. those whose number of hundreds is divisible by 4 without a remainder) are not considered leap days. This corrects the error of 3 days, which accumulates over 400 years. Thus, the average length of the year in the new style turns out to be very close to the period of revolution of the Earth around the Sun.

By the 20th century the difference between the new style and the old (Julian) reached 13 days. Since in our country the new style was introduced only in 1918, the October Revolution, carried out in 1917 on October 25 (old style), is celebrated on November 7 (new style).

The difference between the old and new styles of 13 days will remain in the 21st century, and in the 22nd century. will increase to 14 days.

The new style, of course, is not completely accurate, but an error of 1 day will accumulate according to it only after 3300 years.