At observatories there are instruments with which they determine the time in the most accurate way - they check the clock. Time is set according to the position occupied by the luminaries above the horizon. In order for the clocks of the observatory to run as accurately and evenly as possible in the interval between evenings, when they are checked by the position of the stars, the clocks are placed in deep basements. In such basements, the temperature is constant all year round. This is very important as changes in temperature will affect the running of the watch.

To transmit precise time signals by radio, the observatory has a special sophisticated clock, electrical and radio equipment. The exact time signals transmitted from Moscow are one of the most accurate in the world. Determining the exact time by the stars, storing time with an accurate clock and transmitting it by radio - all this constitutes the Time Service.

WHERE THE ASTRONOMS WORK

Astronomers carry out scientific work at observatories and in astronomical institutes.

The latter are mainly engaged in theoretical research.

After the Great October socialist revolution in our country, the Institute of Theoretical Astronomy in Leningrad, the Astronomical Institute named after V.I. PK Sternberg in Moscow, astrophysical observatories in Armenia, Georgia and a number of other astronomical institutions.

The training and education of astronomers takes place in universities at the Faculties of Mechanics and Mathematics or Physics and Mathematics.

The main observatory in our country is Pulkovskaya. It was built in 1839 near St. Petersburg under the guidance of a prominent Russian scientist. In many countries it is rightly called the astronomical capital of the world.

Simeiz Observatory in Crimea after the Great Patriotic War was completely restored, and not far from it a new observatory was built in the village of Partizanskoe near Bakhchisarai, where the largest reflector telescope in the USSR with a mirror with a diameter of 1 ¼ m is now installed, and soon a reflector with a mirror 2.6 m in diameter will be installed - the third in the largest in the world. Both observatories now constitute one institution - the Crimean Astrophysical Observatory of the USSR Academy of Sciences. There are astronomical observatories in Kazan, Tashkent, Kiev, Kharkov and other places.

At all observatories we have scientific work according to the agreed plan. Achievements of astronomical science in our country help broad strata of working people to develop a correct, scientific understanding of the world around us.

There are many astronomical observatories in other countries as well. Of these, the most famous are the oldest of the existing ones - Paris and Greenwich, from the meridian of which geographic longitudes on the globe are counted (recently this observatory was moved to a new place, further from London, where there are many obstacles for night sky observations). The world's largest telescopes are installed in California at Mount Palomar, Mount Wilson and Lick Observatories. The last one was built in late XIX century, and the first two - already in the XX century.

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I am happy to live in an exemplary and simple way:
Like the sun - like a pendulum - like a calendar
M. Tsvetaeva

Lesson 6/6

Topic Basics of measuring time.

Target Consider the time counting system and its relationship with geographic longitude. To give an idea of ​​the chronology and calendar, the determination of the geographical coordinates (longitude) of the area according to the data of astrometric observations.

Tasks :
1. Educational: practical astrometry about: 1) astronomical methods, instruments and units of measurement, time counting and storage, calendars and chronology; 2) determining the geographical coordinates (longitude) of the area according to astrometric observations. Service of the Sun and exact time. The use of astronomy in cartography. On cosmic phenomena: the revolution of the Earth around the Sun, the revolution of the Moon around the Earth and the rotation of the Earth around its axis and about their consequences - celestial phenomena: sunrise, sunset, daily and annual visible movement and culminations of the luminaries (the Sun, the Moon and the stars), the change in the phases of the Moon ...
2. Upbringing: the formation of a scientific worldview and atheistic education in the course of acquaintance with the history of human knowledge, with the main types of calendars and chronology systems; debunking superstitions associated with the concept of "leap year" and the translation of the dates of the Julian and Gregorian calendars; polytechnic and labor education in the presentation of material about devices for measuring and storing time (clocks), calendars and chronology systems and about practical ways of applying astrometric knowledge.
3. Developing: the formation of skills: to solve problems for calculating the time and dates of chronology and transferring time from one storage system and account to another; perform exercises on the application of the basic formulas of practical astrometry; use a moving map of the starry sky, reference books and the Astronomical calendar to determine the position and conditions of visibility of celestial bodies and the course of celestial phenomena; determine the geographical coordinates (longitude) of the area according to astronomical observations.

Know:
1st level (standard)- time counting systems and units of measurement; the concept of half a day, midnight, a day, the relationship between time and geographic longitude; zero meridian and universal time; zone, local, summer and winter time; methods of translation; our chronology, the origin of our calendar.
2nd level- time counting systems and units of measurement; the concept of half a day, midnight, a day; relationship of time with geographic longitude; zero meridian and universal time; zone, local, summer and winter time; methods of translation; appointment of a precise time service; the concept of chronology and examples; the concept of a calendar and the main types of calendars: lunar, lunisolar, solar (Julian and Gregorian) and the basics of chronology; the problem of creating a permanent calendar. Basic concepts of practical astrometry: the principles of determining the time and geographic coordinates of an area according to astronomical observations. The reasons for the daily observed celestial phenomena generated by the revolution of the Moon around the Earth (change in the phases of the Moon, the apparent movement of the Moon in the celestial sphere).

Be able to:
1st level (standard)- find time universal, average, zone, local, summer, winter;
2nd level- find time universal, average, zone, local, summer, winter; transfer dates from old to new style and back. Solve tasks to determine the geographical coordinates of the place and time of observation.

Equipment: poster "Calendar", PKZN, pendulum and sundial, metronome, stopwatch, quartz clock Earth Globe, tables: some practical applications astronomy. CD- "Red Shift 5.1" (Time-show, Tales of the Universe = Time and seasons). Celestial sphere model; wall map of the starry sky, map of time zones. Maps and photographs of the earth's surface. Table "Earth in Outer Space". Fragments of film strips"Visible movement of heavenly bodies"; "Development of ideas about the Universe"; "How Astronomy Disproved Religious Ideas of the Universe"

Interdisciplinary communication: Geographic coordinates, time counting and orientation methods, cartographic projection (geography, grade 6-8)

During the classes

1. Repetition of what has been learned(10 min).
a) 3 people on individual cards.
1. 1. At what altitude in Novosibirsk (φ = 55º) does the Sun culminate on September 21? [for the second week of October according to PKZN δ = -7º, then h = 90 о -φ + δ = 90 о -55º-7º = 28º]
2. Where on earth are no stars in the southern hemisphere visible? [at the North Pole]
3. How to navigate the terrain by the Sun? [March, September - sunrise in the east, sunset in the west, noon in the south]
2. 1. Noon height The sun is 30º and its declination is 19º. Determine the geographic latitude of the observation site.
2. How are the diurnal paths of the stars relative to the celestial equator? [parallel]
3. How to navigate the terrain using the Pole Star? [north direction]
3. 1. What is the declination of a star if it culminates in Moscow (φ = 56 º ) at an altitude of 69º?
2. How is the axis of the world relative to the earth's axis, relative to the plane of the horizon? [parallel, at an angle to the latitude of the observation site]
3. How to determine the geographical latitude of the area from astronomical observations? [measure the angular height of the North Star]

b) 3 people at the blackboard.
1. Derive the formula for the height of the luminary.
2. Daily paths of stars (stars) at different latitudes.
3. Prove that the height of the pole of the world is equal to the latitude.

v) The rest on their own .
1. What is the greatest height Vega reaches (δ = 38 about 47 ") in the Cradle (φ = 54 about 04")? [ highest height in the upper culmination, h = 90 о -φ + δ = 90 о -54 о 04 "+38 о 47" = 74 о 43 "]
2. Select by PKZN any bright star and write down its coordinates.
3. In what constellation is the Sun today and what are its coordinates? [for the second week of October by PKZN in cons. Virgo, δ = -7º, α = 13 h 06 m]

d) in "Red Shift 5.1"
Find the Sun:
- what information can you get about the sun?
- what are its coordinates today and in what constellation is it?
- how does declination change? [decreases]
- which of the stars that have their own name is closest in angular distance to the Sun and what are its coordinates?
- prove that the Earth is currently moving in orbit approaching the Sun (from the visibility table - the angular diameter of the Sun is growing)

2. New material (20 minutes)
Need to convert attention of pupils:
1. The length of a day and a year depends on the frame of reference in which the motion of the Earth is considered (whether it is associated with fixed stars, the Sun, etc.). The choice of the reference system is reflected in the name of the time unit.
2. The duration of time units is associated with the conditions of visibility (culminations) of celestial bodies.
3. The introduction of the atomic time standard in science was due to the unevenness of the Earth's rotation, which was discovered with an increase in the accuracy of clocks.
4. The introduction of standard time is due to the need to coordinate economic activities in the territory defined by the boundaries of time zones.

Time counting systems. Relationship with geographic longitude. Thousands of years ago, people noticed that much in nature repeats itself: the sun rises in the east and sets in the west, summer replaces winter and vice versa. It was then that the first units of time appeared - day month Year ... With the help of the simplest astronomical instruments, it was found that there are about 360 days in a year, and in about 30 days, the silhouette of the moon goes through a cycle from one full moon to the next. Therefore, the Chaldean sages adopted the sixagesimal number system as a basis: the day was divided into 12 night and 12 day hours , the circle is 360 degrees. Every hour and every degree has been divided by 60 minutes , and every minute - 60 seconds .
However, subsequent more accurate measurements have hopelessly spoiled this perfection. It turned out that the Earth makes a complete revolution around the Sun in 365 days, 5 hours 48 minutes and 46 seconds. The moon, on the other hand, takes from 29.25 to 29.85 days to go around the Earth.
Periodic phenomena accompanied by the diurnal rotation of the celestial sphere and the apparent annual motion of the Sun along the ecliptic underlie various time systems. Time- the main physical quantity that characterizes the successive change of phenomena and states of matter, the duration of their existence.
Short- day, hour, minute, second
Long- year, quarter, month, week.
1. "Starry"time associated with the movement of stars in the celestial sphere. Measured by the hour angle of the vernal equinox: S = t ^; t = S - a
2. "Solar"time associated with: the apparent movement of the center of the Sun's disk along the ecliptic (true solar time) or the movement of the" middle Sun "- an imaginary point moving uniformly along the celestial equator for the same period of time as the true Sun (mean solar time).
With the introduction of the atomic time standard and the International SI system in 1967, the atomic second is used in physics.
Second is a physical quantity numerically equal to 9192631770 periods of radiation corresponding to the transition between hyperfine levels of the ground state of the cesium-133 atom.
All of the above "times" are consistent with each other by special calculations. Average solar time is used in everyday life. . The main unit of sidereal, true and mean solar time is the day. We get sidereal, mean solar and other seconds by dividing the corresponding day by 86400 (24 h, 60 m, 60 s). Day became the first time unit over 50,000 years ago. Day- the period of time during which the Earth makes one complete revolution around its axis relative to any landmark.
Stellar day- the period of rotation of the Earth around its axis relative to fixed stars, is defined as the time interval between two successive upper culminations of the vernal equinox.
True solar day- the period of rotation of the Earth around its axis relative to the center of the Sun's disk, defined as the time interval between two successive culminations of the same name of the center of the Sun's disk.
Due to the fact that the ecliptic is tilted to the celestial equator at an angle of 23 o 26 ", and the Earth revolves around the Sun in an elliptical (slightly elongated) orbit, the speed of the Sun's apparent motion in the celestial sphere and, therefore, the duration of true solar days will constantly change throughout the year. : the fastest near the equinox points (March, September), the slowest near the solstice points (June, January) To simplify time calculations in astronomy, the concept of an average solar day is introduced - the period of rotation of the Earth around its axis relative to the "average Sun".
Average sunny days are defined as the interval of time between two successive homonymous culminations of the "middle sun". They are 3 m 55,009 s shorter than a sidereal day.
24 h 00 m 00 s sidereal time are equal to 23 h 56 m 4.09 s mean solar time. For the definiteness of theoretical calculations, ephemeris (tabular) a second equal to the average solar second on January 0, 1900 at 12 o'clock of the current time, not related to the rotation of the Earth.

About 35,000 years ago, people noticed a periodic change in the appearance of the moon - the change in lunar phases. Phase F a celestial body (Moon, planet, etc.) is determined by the ratio of the largest width of the illuminated part of the disk d to its diameter D: Ф =d / D... Line terminator separates the dark and light parts of the luminary disk. The moon moves around the earth in the same direction in which the earth rotates on its axis: from west to east. The reflection of this movement is the apparent movement of the moon against the background of stars towards the rotation of the sky. Every day the Moon shifts eastward by 13.5 o relative to the stars and completes a full circle in 27.3 days. So the second measure of time after the day was established - month.
Sidereal (stellar) lunar month- the period of time during which the Moon makes one complete revolution around the Earth relative to fixed stars. Equal to 27 d 07 h 43 m 11.47 s.
Synodic (calendar) lunar month- the time interval between two consecutive phases of the same name (usually new moons) of the Moon. Equal to 29 d 12 h 44 m 2.78 s.
The combination of the phenomena of the visible movement of the Moon against the background of stars and the change in the phases of the Moon allows you to navigate by the Moon on the ground (Fig). The moon appears as a narrow crescent in the west and disappears in the rays of dawn with the same narrow crescent in the east. Let us mentally attach a straight line to the lunar crescent to the left. We can read in the sky either the letter "P" - "growing", the "horns" of the month are turned to the left - the month is visible in the west; or the letter "C" - "aging", the "horns" of the month are turned to the right - the month is visible in the east. On a full moon, the moon is visible in the south at midnight.

As a result of observing the change in the position of the Sun above the horizon for many months, a third measure of time has arisen - year.
Year- the period of time during which the Earth makes one complete revolution around the Sun relative to any landmark (point).
Stellar year- sidereal (stellar) period of the Earth's revolution around the Sun, equal to 365.256320 ... average solar days.
Anomalistic year- the time interval between two successive passages of the average Sun through the point of its orbit (usually, perihelion), is equal to 365.259641 ... average solar days.
Tropical year- the time interval between two successive passages of the average Sun through the vernal equinox, equal to 365.2422 ... average solar days or 365 d 05 h 48 m 46.1 s.

World time is defined as the local mean solar time at the zero (Greenwich) meridian ( That, UT- Universal Time). Since in everyday life, local time cannot be used (since in the Cradle it is one thing, and in Novosibirsk it is different (different λ )), therefore it was approved by the Conference on the proposal of the Canadian railway engineer Sanford Fleming(8 February 1879 when speaking at the Canadian Institute in Toronto) standard time, dividing the globe into 24 hour zones (360: 24 = 15 o, 7.5 o each from the central meridian). Zero time zone is located symmetrically about the zero (Greenwich) meridian. The belts are numbered from 0 to 23 from west to east. The real boundaries of the belts are aligned with the administrative boundaries of districts, regions or states. The central meridians of time zones are exactly 15 o (1 hour) apart from each other, therefore, when moving from one time zone to another, the time changes by an integer number of hours, but the number of minutes and seconds does not change. New calendar day (and New Year) start with date lines(demarcation line), passing mainly along the meridian 180 o east longitude near the northeastern border Russian Federation... West of the date line, the day of the month is always one more than to the east of it. When this line is crossed from west to east, the calendar number decreases by one, and when the line from east to west is crossed, the calendar number increases by one, which eliminates the error in time counting when traveling around the world and moving people from the East to the Western hemisphere of the Earth.
Therefore, the International Meridian Conference (1884, Washington, USA), in connection with the development of the telegraph and railway transport, introduces:
- the beginning of the day from midnight, and not from noon, as it was.
- the initial (zero) meridian from Greenwich (Greenwich Observatory near London, founded by J. Flamsteed in 1675, through the axis of the telescope of the observatory).
- counting system standard time
Zone time is determined by the formula: T n = T 0 + n , where T 0 - universal time; n- time zone number.
Daylight saving time- standard time, changed by an integer number of hours by government decree. For Russia, it is equal to the waist, plus 1 hour.
Moscow time- Daylight saving time of the second time zone (plus 1 hour): Tm = T 0 + 3 (hours).
Summer time- Daylight saving time, changed additionally by plus 1 hour by government order for the summer time period in order to save energy resources. Following the example of England, which first introduced daylight saving time in 1908, now there are 120 countries of the world, including the Russian Federation, which annually switches to daylight saving time.
Time zones of the world and Russia
Next, you should briefly familiarize students with the astronomical methods of determining the geographical coordinates (longitude) of the area. Due to the rotation of the Earth, the difference between the moments of the onset of half a day or climax ( climax. What is this phenomenon?) Of stars with known equatorial coordinates at 2 points is equal to the difference in geographical longitudes of points, which makes it possible to determine the longitude of a given point from astronomical observations of the Sun and other luminaries and, conversely, local time at any point with a known longitude.
For example: one of you is in Novosibirsk, the other in Omsk (Moscow). How many of you will observe the upper climax of the center of the Sun before? And why? (note, it means that your watch runs according to Novosibirsk time). Conclusion- depending on the location on Earth (meridian - geographic longitude), the culmination of any star is observed at different times, that is time is related to geographic longitude or T = UT + λ, and the time difference for two points located on different meridians will be T 1 -T 2 = λ 1 - λ 2.Geographic longitude (λ ) of the area is measured to the east of the "zero" (Greenwich) meridian and is numerically equal to the time interval between the same culminations of the same star on the Greenwich meridian ( UT) and at the observation point ( T). Expressed in degrees or hours, minutes and seconds. To determine the geographical longitude of the area, it is necessary to determine the moment of the culmination of any luminary (usually the Sun) with known equatorial coordinates. By translating with the help of special tables or a calculator the observation time from average solar to stellar and knowing the time of the culmination of this star on the Greenwich meridian from the reference book, we can easily determine the longitude of the area. The only difficulty in calculating is the exact translation of units of time from one system to another. The moment of culmination can not be "watched": it is enough to determine the height (zenith distance) of the star at any precisely fixed moment in time, but the calculations will then be rather complicated.
The clock is used to measure time. From the simplest, used in antiquity, are gnomon - a vertical pole in the center of a horizontal platform with divisions, then sand, water (clepsydras) and fire, to mechanical, electronic and atomic ones. An even more accurate atomic (optical) time standard was created in the USSR in 1978. An error of 1 second occurs once every 10,000,000 years!

Time keeping system in our country
1) From July 1, 1919, introduced standard time(decree of the Council of People's Commissars of the RSFSR dated 02/08/1919)
2) In 1930 it is installed Moscow (maternity) the time of the 2nd time zone in which Moscow is located, by translating one hour ahead of the standard time (+3 to the Universal or +2 to the Central European) in order to ensure the brighter part of the day in the daytime (decree of the Council of People's Commissars of the USSR dated 06/16/1930 ). Distribution by time zones of edges and regions changes significantly. Canceled in February 1991 and reinstated from January 1992.
3) By the same Decree of 1930, the transition to daylight saving time in effect since 1917 (April 20 and return on September 20) is canceled.
4) In 1981, the transition to daylight saving time was resumed in the country. By the Decree of the Council of Ministers of the USSR dated October 24, 1980 "On the order of calculating time in the territory of the USSR" summer time is introduced by translating at 0 o'clock on April 1 the clock hands one hour forward, and on October 1 one hour back from 1981. (In 1981, daylight saving time was introduced in the vast majority of developed countries - 70, except for Japan). Later in the USSR, the translation began to be done on the Sunday closest to these dates. The resolution introduced a number of significant changes and approved the newly compiled list of administrative territories assigned to the respective time zones.
5) In 1992, the Presidential Decree was restored, canceled in February 1991, maternity (Moscow) time from January 19, 1992 with the preservation of the transfer to summer time on the last Sunday in March at 2 a.m. for an hour ahead, and for winter time on the last Sunday of September at 3 o'clock in the morning one hour ago.
6) In 1996, by the Decree of the Government of the Russian Federation No. 511 of 23.04.1996, summer time was extended by one month and now ends on the last Sunday of October. V Western Siberia regions that were previously in the MSK + 4 zone switched to MSK + 3 time, joining Omsk time: Novosibirsk region on May 23, 1993 at 00:00, Altai Territory and the Altai Republic on May 28, 1995 at 4:00, Tomsk region on May 1, 2002 at 3:00, Kemerovo region on March 28, 2010 at 02:00. ( the difference with the universal time GMT remains 6 hours).
7) Since March 28, 2010, with the transition to daylight saving time, the territory of Russia began to be located in 9 time zones (from the 2nd to the 11th inclusive, with the exception of the 4th, the Samara region and Udmurtia on March 28, 2010 at 2 a.m. Moscow time) with the same time within each time zone. The boundaries of time zones run along the borders of the constituent entities of the Russian Federation, each constituent entity is included in one zone, with the exception of Yakutia, which is included in 3 zones (MSK + 6, MSK + 7, MSK + 8), and Sakhalin region, which is included in 2 zones (MSK + 7 on Sakhalin and MSK + 8 on the Kuril Islands).

So, for our country in winter time T = UT + n + 1 h , a in summer time T = UT + n + 2 h

You can offer to do laboratory (practical) work at home: Laboratory work"Determination of the coordinates of the terrain by observations of the Sun"
Equipment: gnomon; chalk (pegs); "Astronomical calendar", notebook, pencil.
Work order:
1. Determination of the midday line (direction of the meridian).
With the daily movement of the Sun across the sky, the shadow of the gnomon gradually changes its direction and length. At true noon, it has the smallest length and shows the direction of the midday line - the projection of the celestial meridian onto the plane of the mathematical horizon. To determine the midday line, it is necessary in the morning hours to mark the point at which the shadow of the gnomon falls and draw a circle through it, taking the gnomon as its center. Then you should wait until the shadow of the gnomon touches the circle line a second time. The resulting arc is divided into two parts. The line passing through the gnomon and the middle of the noon arc will be the noon line.
2. Determination of the latitude and longitude of the area from the observations of the Sun.
Observations begin shortly before the moment of true noon, the onset of which is recorded at the moment of exact coincidence of the shadow from the gnomon and the midday line according to a well-adjusted clock running according to standard time. At the same time, the length of the shadow from the gnomon is measured. Along the length of the shadow l at true noon by the time of its occurrence T by daylight saving time, using simple calculations, the coordinates of the area are determined. Preliminarily from the relation tg h ¤ = N / l, where N- the height of the gnomon, find the height of the gnomon at true noon h ¤.
The latitude of the area is calculated by the formula φ = 90-h ¤ + d ¤, where d ¤ is the declination of the Sun. To determine the longitude of the area, use the formula λ = 12 h + n + Δ-D, where n- the number of the time zone, h - the equation of time for the given day (determined according to the data of the "Astronomical calendar"). For winter time D = n+ 1; for summer time D = n + 2.

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1.2.3. True and mean solar time. The equation of time

1.2.4. Julian days

1.2.5. Local time on different meridians. World Time, Standard Time and Daylight Savings Time

1.2.6. The relationship between mean solar and sidereal time

1.2.7. Irregularity of the Earth's rotation

1.2.8. Ephemeris time

1.2.9. Atomic time

1.2.10. Dynamic and coordinate time

1.2.11. Universal Time Systems. UTC

1.2.12. Time of satellite navigation systems

1.3. Astronomical factors

1.3.1. General Provisions

1.3.2. Astronomical refraction

1.3.3. Parallax

1.3.4. Aberration

1.3.5. The proper movement of the stars

1.3.6. Gravitational deflection of light

1.3.7. Earth Pole Movement

1.3.8. Changing the position of the axis of the world in space. Precession

1.3.9. Changing the position of the axis of the world in space. Nutation

1.3.10. Joint accounting of reductions

1.3.11. Calculating the apparent places of stars

2. GEODETIC ASTRONOMY

2.1. Subject and tasks of geodetic astronomy

2.1.1. Using astronomical data in solving geodesy problems

2.1.3. Modern problems and prospects for the development of geodetic astronomy

2.2. Theory of methods of geodetic astronomy

2.2.2. The most favorable conditions for determining the time and latitude in the zenital methods of astronomical determinations

2.3. Instrumentation in geodetic astronomy

2.3.1. Features of instrumentation in geodetic astronomy

2.3.2. Astronomical theodolites

2.3.3. Instruments for measuring and recording time

2.4. Features of observation of luminaries in geodetic astronomy. Reductions of astronomical observations

2.4.1. Methods of sighting the luminaries

2.4.2. Corrections to measured zenith distances

2.4.3. Corrections in measured horizontal directions

2.5. The concept of the exact methods of astronomical definitions

2.5.1 Determination of latitude from measured small differences in zenith distances of pairs of stars in the meridian (Talcott's method)

2.5.2. Methods for determining latitude and longitude from observations of stars at equal heights (methods of equal heights)

2.5.3. Determination of the astronomical azimuth of the direction to the terrestrial object according to the observations of Polar

2.6. Approximate Methods of Astronomical Definitions

2.6.1. Approximate determination of the azimuth of a terrestrial object from the observations of Polar

2.6.2. Approximate determination of latitude from observations of Polar

2.6.3. Approximate determination of longitude and azimuth from the measured zenith distances of the Sun

2.6.4. Approximate determination of latitude from measured zenith distances of the Sun

2.6.5. Determination of the directional angle of the direction to the terrestrial object according to observations of the luminaries

2.7. Aeronautical and nautical astronomy

3. ASTROMETRY

3.1. Astrometry problems and methods for their solution

3.1.1. Subject and tasks of astrometry

3.1.3. Current state and prospects for the development of astrometry

3.2. Fundamental Astrometry Instruments

3.2.2. Classic astrooptical instruments

3.2.3. Modern astronomical instruments

3.3. Creation of fundamental and inertial coordinate systems

3.3.1. General Provisions

3.3.2. Theoretical foundations for determining the coordinates of stars and their changes

3.3.3. Building a fundamental coordinate system

3.3.4. Building an inertial coordinate system

3.4.1. Setting the time scale

3.4.2. Determination of the parameters of the orientation of the Earth

3.4.3. Organization of the service of time, frequency and determination of the parameters of the Earth's orientation

3.5. Fundamental astronomical constants

3.5.1. General Provisions

3.5.2. Classification of fundamental astronomical constants

3.5.3. International System of Astronomical Constants

BIBLIOGRAPHIC LIST

ANNEXES

1. System of fundamental astronomical constants MAC 1976

1.2. Measuring time in astronomy

1.2.1. General Provisions

One of the tasks of geodetic astronomy, astrometry and space geodesy is to determine the coordinates celestial bodies at a given moment in time. Astronomical time scales are constructed by the national time services and the International Time Bureau.

All known methods of constructing continuous time scales are based on periodic processes, For example:

- rotation of the Earth around its axis;

- the revolution of the Earth around the Sun in its orbit;

- the rotation of the Moon around the Earth in its orbit;

- swinging of a pendulum under the influence of gravity;

- elastic vibrations of a quartz crystal under the action of an alternating current;

- electromagnetic vibrations of molecules and atoms;

- radioactive decay of atomic nuclei and other processes.

The time system can be set with the following parameters:

1) mechanism - a phenomenon that provides a periodically repeating process (for example, the daily rotation of the Earth);

2) scale - a period of time during which the process is repeated;

3) starting point, zero point - the moment of the beginning of the repetition of the process;

4) way of counting time.

In geodetic astronomy, astrometry, celestial mechanics, sidereal and solar time systems are used, based on the rotation of the Earth around its axis. This periodic movement is eminently uniform, unlimited in time and continuous throughout the entire existence of mankind.

In addition, astrometry and celestial mechanics use

Ephemeris and dynamic time systems as an ideal

the structure of a uniform time scale;

System atomic time- practical implementation of a perfectly uniform time scale.

1.2.2. Sidereal time

Sidereal time is denoted by s. The parameters of the sidereal time system are:

1) mechanism - the rotation of the Earth around its axis;

2) scale - sidereal days equal to the time interval between two successive upper culminations of the vernal equinox point

v observation point;

3) the starting point on the celestial sphere is the vernal equinox point, zero point (the beginning of a sidereal day) is the moment of the point's upper culmination;

4) way of counting. The measure of sidereal time is the hour angle of a point

vernal equinox, t. It is impossible to measure it, but for any star the expression is true

therefore, knowing the right ascension of the star and calculating its hourly angle t, one can determine the sidereal time s.

Distinguish true, average and quasi-true points of gamma (the separation is related to the astronomical factor of nutation, see paragraph 1.3.9), relative to which the true, mean and quasi true sidereal time.

The sidereal time system is used to determine the geographic coordinates of points on the surface of the Earth and the azimuths of the direction to terrestrial objects, to study the irregularities of the Earth's daily rotation, and to establish the zero points of the scales of other time measurement systems. This system, although widely used in astronomy, is inconvenient in everyday life. The change of day and night, due to the apparent diurnal movement of the Sun, creates a quite definite cycle in human activity on Earth. Therefore, for a long time, the reckoning of time has been carried out according to the diurnal movement of the Sun.

1.2.3. True and mean solar time. The equation of time

True solar time system (or true solar time- m) is used for astronomical or geodetic observations of the Sun. System parameters:

1) mechanism - the rotation of the Earth around its axis;

2) scale - true solar day- the time interval between two successive lower culminations of the center of the true Sun;

3) the starting point is the center of the disc of the true Sun -, zero point - true midnight, or the moment of the lower culmination of the center of the disc of the true Sun;

4) way of counting. The measure of measuring true solar time is the geocentric hourly angle of the true sun t plus 12 hours:

m = t + 12h.

The unit of true solar time - a second, equal to 1/86400 of true solar days, does not satisfy the basic requirement for a unit of time measurement - it is not constant.

The reasons for the inconstancy of the true solar time scale are

1) uneven movement of the Sun along the ecliptic due to the ellipticity of the Earth's orbit;

2) an uneven increase in the right ascension of the Sun during the year, since the Sun is along the ecliptic, inclined to the celestial equator at an angle of approximately 23.50.

For these reasons, the application of the true solar time system is inconvenient in practice. The transition to a uniform solar time scale occurs in two stages.

Stage 1 transition to fictitious average ecliptic sun... On this

At this stage, the uneven motion of the Sun along the ecliptic is eliminated. Irregular motion in an elliptical orbit is replaced by uniform motion in a circular orbit. The true sun and the mean ecliptic sun coincide when the Earth passes through the perihelion and aphelion of its orbit.

Stage 2 transition to middle equatorial sun moving equal

numbered along the celestial equator. Here, the unevenness of the increase in the right ascension of the Sun, caused by the inclination of the ecliptic, is excluded. The true sun and the mean equatorial sun simultaneously pass the vernal and autumnal equinoxes.

As a result of the above actions, a new time measurement system is introduced - mean solar time.

Average solar time is denoted by m. The parameters of the mean solar time system are:

1) mechanism - the rotation of the Earth around its axis;

2) scale - average day - the time interval between two successive lower culminations of the average equatorial Sun  eq;

3) starting point - mean equatorial sun eq, zero point - middle midnight, or the moment of the lower climax of the middle equatorial Sun;

4) way of counting. The measure of the mean time is the geocentric hour angle of the mean equatorial Sun t eq plus 12 hours.

m = teq + 12h.

It is impossible to determine the mean solar time directly from observations, since the mean equatorial sun is a fictitious point on the celestial sphere. Average solar time is calculated from true solar time, determined from observations of the true sun. The difference between the true solar time m and the mean solar time m is called equation of time and is indicated by:

M - m = t - t mean eq. ...

The equation of time is expressed by two sinusoids with an annual and semi-annual

new periods:

1 + 2 -7.7m sin (l + 790) + 9.5m sin 2l,

where l is the ecliptic longitude of the mean ecliptic sun.

The graph is a curve with two maxima and two minima, which in a Cartesian rectangular coordinate system has the form shown in Fig. 1.18.

Figure 1.18. Equation of time graph

The values ​​of the equation of time are in the range from + 14m to –16m.

In the Astronomical Yearbook, for each date, the value of E is given, equal to

E = + 12 h.

WITH this value, the relationship between the mean solar time and the hour angle of the true Sun is determined by the expression

m = t -E.

1.2.4. Julian days

With a precise definition numerical value the interval of time between two distant dates it is convenient to use the continuous counting of the day, which in astronomy is called Julian days.

The beginning of counting Julian days is the average Greenwich noon on January 1, 4713 BC, from the beginning of this period, the average solar days are counted and numbered so that each calendar date corresponds to a certain Julian day, denoted briefly JD. So, the epoch 1900, January 0.12h UT corresponds to the Julian date JD 2415020.0, and the epoch 2000, January 1, 12h UT corresponds to JD2451545.0.

Exact time

For measuring short periods of time in astronomy, the basic unit is the average duration of a solar day, i.e. the average time interval between the two upper (or lower) climaxes of the center of the Sun. The average value has to be used because the length of the sunny day fluctuates slightly throughout the year. This is due to the fact that the Earth does not revolve around the Sun in a circle, but in an ellipse, and the speed of its movement changes slightly. This causes small 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 the moment of the culmination of the Sun on it. It is more convenient and more accurate to mark the moments of the climax of the stars, since the difference between the moments of the climax of any star and the Sun is precisely known for any time. Therefore, to determine the exact time with the help of special optical devices, they mark the moments of the climax of the stars and check the correctness of the clock, "keeping" time, using them. The time determined in this way would be absolutely accurate if the observed rotation of the firmament occurred at a strictly constant angular velocity. However, it turned out that the speed of rotation of the Earth around its axis, and hence the apparent rotation of the celestial sphere, undergoes very small changes over time. Therefore, to "store" the exact time, a special atomic clock is 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. Comparison of the time determined by the atomic clock and the apparent motion of the stars allows one 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 precise time service, which exists in many countries.

Precise time signals by radio are received by navigators of the sea and air fleet, 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.

Time counting. Determination of geographic longitude. The calendar

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

Since ancient times, people have used the duration of either the lunar month or the solar year to count large periods of time, 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 days and with the length of the lunar month - the period of the lunar phase change (about 29.5 days). This is the difficulty in 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. The southern pastoralists usually used the lunar months. A year of 12 lunar months contained 355 solar days. To coordinate the calculation of time according to the Moon and the Sun, it was necessary to set 12 or 13 months in the year and insert additional days into the year. Simpler and more convenient was the solar calendar, which was used in Ancient egypt... Currently, in most countries of the world, the solar calendar is also adopted, but of a more perfect device, called the Gregorian, which is discussed further.

When compiling the 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 an integer number of solar days, since it is inconvenient to start the year at different times of the day.

These conditions were met by the calendar developed by the Alexandrian astronomer Sozigenes and introduced in 46 BC. in Rome by Julius Caesar. Subsequently, as you know, from the course of physical geography, he received the name of the 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 is called a leap year. Leap years in the Julian calendar are those years whose numbers are evenly divisible by 4.

The average length of a year according to this calendar is 365 days 6 hours, i.e. it is about 11 minutes longer than the true one. Because of this, the old style lagged behind the actual passage 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 in which the number of hundreds is divisible by 4 without a remainder) are not considered leap. This is how the error of 3 days, accumulating over 400 years, is corrected. Thus, the average length of a year in the new style turns out to be very close to the period of the Earth's revolution around the Sun.

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

The difference between the old and new styles of 13 days will remain in the XXI century, and in the XXII century. will increase to 14 days.

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