Keeping time astronomy. Account of time. Definition of geographic longitude. The calendar. Atomic cesium clock
I am happy to live exemplary and simple:
Like the sun - like a pendulum - like a calendar
M. Tsvetaeva
Lesson 6/6
Topic Fundamentals of measuring time.
Target Consider the time counting system and its relationship with geographic longitude. Give an idea of the chronology and calendar, determining the geographical coordinates (longitude) of the area according to astrometric observations.
Tasks
:
1. educational: practical astrometry about: 1) astronomical methods, instruments and units of measurement, counting and keeping time, calendars and chronology; 2) determining the geographical coordinates (longitude) of the area according to the data of astrometric observations. Services of the Sun and exact time. Application of astronomy in cartography. About 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 their consequences - celestial phenomena: sunrise, sunset, daily and annual visible movement and culminations of the luminaries (Sun, Moon and stars), change of phases of the Moon .
2. nurturing: 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 concepts of "leap year" and the translation of the dates of the Julian and Gregorian calendars; polytechnic and labor education in the presentation of material on instruments for measuring and storing time (hours), calendars and chronology systems, and on practical methods for applying astrometric knowledge.
3. Educational: the formation of skills: solve problems for calculating the time and dates of the 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 mobile map of the starry sky, reference books and the Astronomical calendar to determine the position and conditions for the 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 noon, midnight, day, the relationship of time with geographic longitude; zero meridian and universal time; zone, local, summer and winter time; translation methods; our reckoning, the origin of our calendar.
2nd level- time counting systems and units of measurement; concept of noon, midnight, day; connection of time with geographic longitude; zero meridian and universal time; zone, local, summer and winter time; translation methods; appointment of the exact 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 geographical coordinates of the area according to astronomical observations. Causes of daily observed celestial phenomena generated by the revolution of the Moon around the Earth (change of phases of the Moon, apparent movement of the Moon in the celestial sphere).
Be able to:
1st level (standard)- Find the time of the world, average, zone, local, summer, winter;
2nd level- Find the time of the world, average, zone, local, summer, winter; convert dates from old to new style and vice versa. Solve problems 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 of astronomy. CD- "Red Shift 5.1" (Time-show, Stories about the Universe = Time and seasons). Model of the celestial sphere; 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 filmstrips"Visible movement of heavenly bodies"; "Development of ideas about the Universe"; "How Astronomy Refuted Religious Ideas about the Universe"
Interdisciplinary communication: Geographical coordinates, time counting and orientation methods, map projection (geography, grades 6-8)
During the classes
1. Repetition of what has been learned(10 min).
a) 3 people on individual cards.
1.
1. At what height in Novosibirsk (φ= 55º) does the Sun culminate on September 21? [for the second week of October, according to the PKZN δ=-7º, then h=90 o -φ+δ=90 o -55º-7º=28º]
2. Where on earth are no stars of 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. Sun's midday altitude is 30º and its declination is 19º. Determine the geographic latitude of the observation site.
2. How are the daily paths of stars relative to the celestial equator? [parallel]
3. How to navigate the terrain using the North Star? [direction north]
3.
1. What is the declination of a star if it culminates in Moscow (φ= 56 º
) at a height of 69º?
2. How is the axis of the world relative to the earth's axis, relative to the horizon plane? [parallel, at the angle of the geographical 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 board.
1. Derive the formula for the height of the luminary.
2. Daily paths of the luminaries (stars) at different latitudes.
3. Prove that the height of the world pole is equal to the geographic latitude.
v) The rest on their own
.
1. What is the highest height Vega reaches (δ=38 o 47") in the Cradle (φ=54 o 04")? [maximum height at the top climax, h=90 o -φ+δ=90 o -54 o 04 "+38 o 47"=74 o 43"]
2. Select any bright star according to the PCZN and write down its coordinates.
3. In what constellation is the Sun today and what are its coordinates? [for the second week of October according to the PCDP in cons. Virgo, δ=-7º, α=13 h 06 m]
d) in "Red Shift 5.1"
Find the Sun:
What information can be obtained about the Sun?
- what are its coordinates today and in what constellation is it located?
How does the declination change? [decreases]
- which of the stars with its 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 pay student attention:
1. The length of the day and 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 reference system is reflected in the name of the unit of time.
2. The duration of time counting units is related to the conditions of visibility (culminations) of celestial bodies.
3. The introduction of the atomic time standard in science was due to the non-uniformity of the Earth's rotation, which was discovered with increasing clock accuracy.
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 many things in nature repeat themselves: the Sun rises in the east and sets in the west, summer follows winter and vice versa. It was then that the first units of time arose - day month Year
. Using 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 sexagesimal number system as the basis: the day was divided into 12 night and 12 day hours
, the circle is 360 degrees. Every hour and every degree was divided by 60 minutes
, and every minute - by 60 seconds
.
However, subsequent more accurate measurements 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 bypass the Earth.
Periodic phenomena accompanied by daily rotation of the celestial sphere and the apparent annual movement of the Sun along the ecliptic
are the basis of various time counting systems. Time- the main physical quantity characterizing 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.
"stellar"the time associated with the movement of stars on the celestial sphere. Measured by the hour angle of the vernal equinox point: S \u003d t ^; t \u003d 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 "average Sun" - an imaginary point moving uniformly along the celestial equator in the same time interval as the true Sun (average solar time).
With the introduction in 1967 of the atomic time standard and the International SI system, the atomic second is used in physics.
Second- 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 the above "times" are consistent with each other by special calculations. Mean solar time is used in everyday life
. The basic 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). The day became the first unit of time measurement over 50,000 years ago. Day- the period of time during which the Earth makes one complete rotation around its axis relative to any landmark.
sidereal day- the period of rotation of the Earth around its axis relative to the fixed stars, is defined as the time interval between two successive upper climaxes of the vernal equinox.
true solar day- the period of rotation of the Earth around its axis relative to the center of the solar disk, defined as the time interval between two successive climaxes of the same name of the center of the solar disk.
Due to the fact that the ecliptic is inclined to the celestial equator at an angle of 23 about 26 ", and the Earth revolves around the Sun in an elliptical (slightly elongated) orbit, the speed of the apparent movement of the Sun in the celestial sphere and, therefore, the duration of a true solar day will constantly change throughout the year : the fastest near the equinoxes (March, September), the slowest near the solstices (June, January) To simplify the calculations of time in astronomy, the concept of a mean solar day is introduced - the period of rotation of the Earth around its axis relative to the "average Sun".
Mean solar day are defined as the time interval between two successive climaxes of the same name of the "middle Sun". They are 3 m 55.009 s shorter than a sidereal day.
24 h 00 m 00 s of sidereal time are equal to 23 h 56 m 4.09 s of mean solar time. For definiteness of theoretical calculations, it is accepted ephemeris (table) second equal to the mean solar second on January 0, 1900 at 12 o'clock equal 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 - a change in the lunar phases. Phase F celestial body (Moon, planets, etc.) is determined by the ratio of the largest width of the illuminated part of the disk d to its diameter D: F=d/D. Line terminator separates the dark and light parts of the luminary's disk. The moon moves around the earth in the same direction in which the earth rotates around its axis: from west to east. The display of this movement is the apparent movement of the Moon against the background of the stars towards the rotation of the sky. Every day, the Moon moves to the east 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 (star) lunar month- the period of time during which the moon makes one complete revolution around the earth relative to the fixed stars. Equals 27 d 07 h 43 m 11.47 s .
Synodic (calendar) lunar month- the time interval between two successive phases of the same name (usually new moons) of the moon. Equals 29 d 12 h 44 m 2.78 s . .jpg)
The totality of the phenomena of the visible movement of the Moon against the background of stars and the change in the phases of the Moon makes it possible to navigate the Moon on the ground (Fig.). The moon appears as a narrow crescent in the west and disappears in the rays of the morning dawn with the same narrow crescent in the east. Mentally attach a straight line to the left of the crescent moon. 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" - "getting old", 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 observations of the change in the position of the Sun above the horizon for many months, a third measure of time arose - year.
Year- the period of time during which the Earth makes one complete revolution around the Sun relative to any reference point (point).
sidereal year- sidereal (stellar) period of the Earth's revolution around the Sun, equal to 365.256320 ... mean 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 ... mean solar days.
tropical year- the time interval between two successive passages of the average Sun through the vernal equinox, equal to 365.2422... mean solar days or 365 d 05 h 48 m 46.1 s.
Universal Time defined as local mean solar time at the zero (Greenwich) meridian ( That, UT- Universal Time). Since in everyday life you cannot use local time (since it is one in Kolybelka, and another in Novosibirsk (different λ
)), which is why it was approved by the Conference at the suggestion of a Canadian railway engineer Sanford Fleming(February 8 1879
when speaking at the Canadian Institute in Toronto) standard time, dividing the globe into 24 time zones (360:24 = 15 o, 7.5 o from the central meridian). The zero time zone is located symmetrically with respect to 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, so when moving from one time zone to another, time changes by an integer number of hours, and the number of minutes and seconds does not change. The new calendar day (and the New Year) starts on date lines(demarcation line), passing mainly along the meridian of 180 o east longitude near the northeastern border of the Russian Federation. To the west of the date line, the day of the month is always one more than to the east of it. When crossing this line from west to east, the calendar number decreases by one, and when crossing the line from east to west, the calendar number increases by one, which eliminates the error in counting time when traveling around the world and moving people from the Eastern 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 observatory's telescope).
- counting system standard time
Standard 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 to an integer number of hours by government decree. For Russia, it is equal to the belt, plus 1 hour.
Moscow time- daylight saving time of the second time zone (plus 1 hour): Tm \u003d T 0 + 3
(hours).
Summer time- standard standard time, which is changed by an additional plus 1 hour by government order for the period of summer time in order to save energy resources. Following the example of England, which introduced summer time for the first time in 1908, now 120 countries of the world, including the Russian Federation, annually switch to summer time.
Time zones of the world and Russia
Next, students should be briefly introduced to astronomical methods for determining the geographical coordinates (longitude) of the area. Due to the Earth's rotation, the difference between noon or culmination times ( climax. What is this phenomenon?) of stars with known equatorial coordinates at 2 points is equal to the difference in the geographical longitudes of the 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 second in Omsk (Moscow). Which of you will observe the upper culmination of the center of the Sun earlier? And why? (note, it means that your clock is on the time of Novosibirsk). Conclusion- depending on the location on Earth (meridian - geographic longitude), the climax of any luminary 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 \u003d λ 1 - λ 2.Geographic longitude (λ
) of the area is counted east of the "zero" (Greenwich) meridian and is numerically equal to the time interval between the climaxes of the same name of the same luminary on the Greenwich meridian ( UT) and at the observation point ( T). Expressed in degrees or hours, minutes and seconds. To determine
geographic longitude of the area, it is necessary to determine the moment of climax of any luminary (usually the Sun) with known equatorial coordinates. By translating with the help of special tables or a calculator the time of observations from the mean solar to the stellar and knowing from the reference book the time of the culmination of this luminary on the Greenwich meridian, we can easily determine the longitude of the area. The only difficulty in the calculations is the exact conversion of units of time from one system to another. The moment of culmination can not be "guarded": it is enough to determine the height (zenith distance) of the luminary at any precisely fixed moment in time, but then the calculations will be quite complicated.
Clocks are used to measure time. From the simplest, used in antiquity, is gnomon
- a vertical pole in the center of a horizontal platform with divisions, then sand, water (clepsydra) and fire, up to mechanical, electronic and atomic. An even more accurate atomic (optical) time standard was created in the USSR in 1978. An error of 1 second occurs every 10,000,000 years!
Timekeeping system in our country
1) From July 1, 1919, it is introduced standard time(Decree of the Council of People's Commissars of the RSFSR of February 8, 1919)
2) In 1930 it is established Moscow (maternity)
the time of the 2nd time zone in which Moscow is located, moving one hour ahead compared to the standard time (+3 to the Universal or +2 to the Central European) in order to provide a brighter part of the day in the daytime (decree of the Council of People's Commissars of the USSR of 06/16/1930 ). The time zone distribution of the edges and regions changes significantly. Canceled in February 1991 and restored again from January 1992.
3) The same Decree of 1930 abolishes the transition to summer time, which has been in force since 1917 (April 20 and return on September 20).
4) In 1981, the transition to summer time resumes in the country. Decree of the Council of Ministers of the USSR of October 24, 1980 "On the procedure for calculating time on the territory of the USSR" summer time is introduced
by transferring the hands of the clock to 0 hours on April 1 an hour forward, and on October 1 an hour ago since 1981. (In 1981, daylight saving time was introduced in the vast majority of developed countries - 70, except for Japan). In the future, in the USSR, the translation began to be done on the Sunday closest to these dates. The resolution made a number of significant changes and approved a newly compiled list of administrative territories assigned to the corresponding time zones.
5) In 1992, by the Decrees of the President, canceled in February 1991, maternity (Moscow) time was restored from January 19, 1992, while maintaining the transfer to summer time on the last Sunday of March at 2 am one hour ahead, and to winter time on the last Sunday of September at 3 one hour of the night one hour ago.
6) In 1996, by Decree of the Government of the Russian Federation No. 511 of April 23, 1996, summer time is extended by one month and now ends on the last Sunday of October. In Western Siberia, the regions that were previously in the MSK + 4 zone switched to MSK + 3 time, joining the 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 May 1, 2002 at 03:00, Kemerovo region March 28, 2010 at 02:00. ( the difference with universal time GMT remains 6 hours).
7) From March 28, 2010, during the transition to summer 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 - Samara region and Udmurtia on March 28, 2010 at 2 a.m. they switched to Moscow time) with the same time within each time zone. The boundaries of time zones pass along the borders of the subjects of the Russian Federation, each subject is included in one zone, with the exception of Yakutia, which is included in 3 zones (MSK + 6, MSK + 7, MSK + 8), and the 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"Determining the coordinates of the terrain from observations of the Sun"
Equipment: gnomon; chalk (pegs); "Astronomical calendar", notebook, pencil.
Work order:
1. Determination of the noon line (meridian direction).
With the daily movement of the Sun across the sky, the shadow from the gnomon gradually changes its direction and length. At true noon, it has the smallest length and shows the direction of the noon line - the projection of the celestial meridian onto the plane of the mathematical horizon. To determine the noon line, it is necessary in the morning hours to mark the point at which the shadow from the gnomon falls and draw a circle through it, taking the gnomon as its center. Then you should wait until the shadow from the gnomon touches the circle line for the 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. Determining 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 fixed at the moment of the exact coincidence of the shadow from the gnomon and the noon line according to well-calibrated clocks running according to standard time. At the same time, the length of the shadow from the gnomon is measured. By the length of the shadow l at true noon at the time of its occurrence T d according to standard time, using simple calculations, determine the coordinates of the area. Previously from the relation tg h ¤ \u003d N / l, where H- 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 solar declination. To determine the longitude of the area, use the formula λ=12h+n+Δ-D, where n- time zone number, h - equation of time for a 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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Exact time
To measure short periods of time in astronomy, the basic unit is the average duration of a solar day, i.e. the average time interval between two upper (or lower) culminations of the center of the Sun. The average value has to be used because the duration of the solar day varies 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 small irregularities in the apparent movement of the Sun along the ecliptic during 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 exact moment of the culmination of the Sun on them. It is more convenient and accurate to mark the moments of the climax of the stars, since the difference in 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 instruments, the moments of the climaxes of the stars are noted and they check the correctness of the clock that “stores” the time. The time thus determined 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, special atomic clocks are now used, the course of which is controlled by oscillatory processes in atoms occurring at a constant frequency. The clocks of individual observatories are checked against atomic time signals. Comparison of the time determined by atomic clocks and by the apparent motion of the stars makes it possible to study the irregularities in the rotation of the Earth.
Determination of the exact time, its storage and transmission by radio to the entire population is the task of the exact time service, which exists in many countries.
The exact time signals on the 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.
Account of time. Definition of geographic longitude. The 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 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 calculate long periods of time, i.e. the duration of the revolution of the sun 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 incommensurable with days and with the length of the lunar month - the period of the change of lunar phases (about 29.5 days). This makes it difficult to create a simple and convenient calendar. Over the centuries of human history, 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 pastoral peoples usually used the lunar months. A year consisting of 12 lunar months contained 355 solar days. To coordinate the calculation of time according to the Moon and according to the Sun, it was necessary to establish 12 or 13 months in a year and insert additional days into the year. The solar calendar, which was used in ancient Egypt, was simpler and more convenient. At present, in most countries of the world, a solar calendar is also adopted, but a more advanced device, called the Gregorian, which is discussed below.
When compiling the calendar, it must be taken into account that the duration of the calendar year should be as close as possible to the duration of the revolution of the Sun 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 satisfied by the calendar developed by the Alexandrian astronomer Sosigenes and introduced in 46 BC. in Rome by Julius Caesar. Subsequently, as you know, from the course of physical geography, it was called the Julian or old style. In this calendar, 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 evenly divisible by 4.
The average length of the 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 flow of time by about 3 days for 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 years. This corrects the error of 3 days, accumulating over 400 years. Thus, the average length of the year in the new style is 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 the new style was introduced in our country only in 1918, the October Revolution, which took place 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 continue into 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 in it only after 3300 years.
Each astronomical observation must be accompanied by data on the time of its execution. The accuracy of the moment of time can be different, depending on the requirements and properties of the observed phenomenon. So, for example, in ordinary observations of meteors and variable stars, it is quite sufficient to know the moment with an accuracy of up to a minute. Observations of solar eclipses, occultations of stars by the Moon, and especially observations of the motion of artificial satellites of the Earth, require marking the moments with an accuracy of no less than a tenth of a second. Accurate astrometric observations of the daily rotation of the celestial sphere force us to use special methods of registering moments of time with an accuracy of 0.01 and even 0.005 seconds!
Therefore, one of the main tasks of practical astronomy is to obtain accurate time from observations, store it and communicate time data to consumers.
To keep time, astronomers have very accurate clocks, which they regularly check by determining the moments of the climaxes of the stars with the help of special instruments. The transmission of exact time signals by radio allowed them to organize a world time service, that is, to link all observatories engaged in observations of this kind into one system.
The responsibility of the Time Services, in addition to broadcasting accurate time signals, also includes the transmission of simplified signals, which are well known to all radio listeners. These are six short signals, “dots”, which are given before the start of a new hour. The moment of the last "point", up to a hundredth of a second, coincides with the beginning of a new hour. The amateur astronomer is advised to use these signals to check his watch. When checking the clock, we should not translate it, since in this case I spoil the mechanism, and the astronomer must take care of his watch, since this is one of his main instruments. He must determine the "correction of the clock" - the difference between the exact time and their readings. These corrections should be systematically determined and recorded in the observer's diary; further study of them will allow you to determine the course of the clock and study them well.
Of course, it is desirable to have the best possible watch at your disposal. What should be understood by the term "good hours"?
It is necessary that they keep their course as accurately as possible. Let's compare two copies of ordinary pocket watches:
The positive sign of the correction means that in order to obtain the exact time, it is necessary to add an amendment to the clock reading.
In the two halves of the tablet are records of clock corrections. Subtracting the upper correction from the lower correction and dividing by the number of days elapsed between determinations, we obtain the daily clock rate. The progress data is given in the same table.
Why do we call some watches bad and others good? For the first hours, the correction is close to zero, but their course changes irregularly. For the second, the correction is large, but the course is uniform. The first clock is suitable for such observations that do not require a time stamp more accurate than to the minute. Their readings cannot be interpolated, and they must be checked several times a night.
The second, "good clock", is suitable for performing more complex observations. Of course, it is useful to check them more often, but it is possible to interpolate their readings for intermediate moments. Let's show this with an example. Let us assume that the observation was made on November 5 at 23:32:46. according to our hours. The check of the clock, carried out at 5 pm on November 4, gave a correction of +2 m. 15 s. The daily course, as can be seen from the table, is +5.7 s. From 17:00 on November 4 until the moment of observation, 1 day and 6.5 hours or 1.27 days passed. Multiplying this number by the daily rate, we get +7.2 s. Therefore, the clock correction at the time of observation was not 2 m. 15 s, but +2 m. 22 s. We add it to the moment of observation. So, the observation was made on November 5 at 23:35:8.
At the observatories there are instruments with the help of 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 observatory clock to run as accurately and evenly as possible in the interval between evenings, when they are checked by the position of the stars, the clock is placed in deep cellars. In such cellars, a constant temperature is maintained throughout the year. This is very important as temperature changes affect the running of the clock.
To transmit accurate time signals by radio, the observatory has special sophisticated clock, electrical and radio equipment. The exact time signals transmitted from Moscow are among the most accurate in the world. Determining the exact time from the stars, keeping time with accurate clocks and transmitting it by radio - all this constitutes the Time Service.
WHERE ASTRONOMERS WORK
Astronomers conduct scientific work at observatories and astronomical institutes.
The latter are mainly engaged in theoretical research.
After the Great October Socialist Revolution in our country, the Institute of Theoretical Astronomy was established in Leningrad, the Astronomical Institute. P.K. Sternberg in Moscow, astrophysical observatories in Armenia, Georgia and a number of other astronomical institutions.
The training and education of astronomers takes place at universities at the Mechanics and Mathematics or Physics and Mathematics faculties.
The main observatory in our country is Pulkovo. 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.
The Simeiz Observatory in the Crimea was completely restored after the Great Patriotic War, and not far from it a new observatory was built in the village of Partizanskoye near Bakhchisarai, where the largest in the USSR reflecting telescope with a mirror with a diameter of 1 ¼ m is now installed, and soon a reflector with a mirror with a diameter of 1 ¼ m will be installed. at 2.6 m - the third largest in the world. Both observatories now form 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 our observatories, scientific work is being carried out according to an agreed plan. Achievements in astronomical science in our country are helping broad sections of the working people develop a correct, scientific idea of the world around us.
Many astronomical observatories exist in other countries as well. Of these, the oldest of the existing ones are the most famous - Paris and Greenwich, from the meridian of which geographic longitudes on the globe are counted (recently, this observatory was moved to a new location, further from London, where there are many interferences for night sky observations). The largest telescopes in the world are installed in California at the Mount Palomar, Mount Wilson and Lick observatories. The last of them was built at the end of the 19th century, and the first two - already in the 20th century.
“The concept of a certain period of time we need
as a scale, namely time, because time,
taken by itself is not such a scale…”.
Plotinus
After studying this topic, you:
- learn about the history of the modern calendar; what is "stellar" and "solar" time and is there an equation of time; who in economically developed countries is the keeper of the exact time; What calendar do we live by? about the history of instruments for measuring time;
- be able to tell the story of the modern calendar; explain what "star" and "solar" time are; explain the differences between true days, days and sidereal days; explain what the equation of time is; talk about instruments for measuring time that were used in antiquity; name one of these devices that is still in use today.
Before you start mastering the material on this topic, listen to the video lecture by Surdin Vladimir Georgievich "Astronomical time and calendar".
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All life and activities of people pass in time. Observing the change of day and night, people have long perceived the passage of time, but they learned to measure it much later.
Measures for measuring time are taken from nature itself: shorter ones are closely related to the rotation of the Earth around its axis, and long ones - with the movement of the Moon and our planet in orbit around the Sun.
Significant difficulties arose in establishing standards for measuring time. Measures of time are natural units taken by a person from the world around him - this is a day, a month and a year. It is important that they are incommensurable.
Units for measuring periods of time, less than a day - an hour, a minute, a second and its fractions - were created by man himself. Over time, he learned not only to measure these conventional units of time, but also to store them. To measure longer periods of time, man used periodic natural phenomena. A system for counting significant periods of time, based on periodic phenomena of the surrounding world, is commonly called a calendar. It is the calendar that allows you to set a certain order for counting days in a year; it is inseparable from human culture.
The calendar, which we constantly use at the present time, did not appear immediately; it has its own long, very complex history, which has not yet been completed to this day, since the modern calendar cannot be called perfect.
Time. Units of measurement and counting time
Time- the main physical quantity characterizing the successive change of phenomena and states of matter, the duration of their existence.
Historically, all basic and derived units of time are determined on the basis of astronomical observations of the course of celestial phenomena, due to the rotation of the Earth around its axis, the rotation of the Moon around the Earth and the rotation of the Earth around the Sun. To measure and calculate time in astrometry, different reference systems are used, associated with certain celestial bodies or certain points of the celestial sphere. The most widespread are "star" and "solar" time. With the introduction in 1967 of the atomic time standard and the International SI system, the atomic second is used in physics.
"Star" and " solar time are consistent with each other by special calculations. In everyday life, mean solar time is used.
Determination of the exact time, its storage and transmission by radio constitute the work of the Precise Time Service, which exists in all developed countries of the world, including Russia.
The basic unit of sidereal, true and mean solar time is the day. Sidereal, mean solar and other seconds are obtained by dividing the corresponding day by 86400 (24 hours 60 minutes 60 seconds). The day became the first unit of time measurement over 50,000 years ago.
Day- the period of time during which the Earth makes one complete rotation around its axis relative to any landmark.
stellarday- the period of rotation of the Earth around its axis relative to the fixed stars, is defined as the time interval between two successive upper climaxes of the vernal equinox.
true solarday- the period of rotation of the Earth around its axis relative to the center of the solar disk, defined as the time interval between two successive climaxes of the same name of the center of the solar disk.
Due to the fact that the ecliptic is inclined to the celestial equator at an angle, and the Earth revolves around the Sun in an elliptical orbit, the speed of the apparent movement of the Sun in the celestial sphere. Consequently, throughout the year, the duration of a true solar day will constantly change: the fastest near the equinoxes (March, September), the slowest near the solstices (June, January).
To simplify the calculations of time in astronomy, the concept of a mean solar day has been introduced - the period of rotation of the Earth around its axis relative to the "average Sun".
Equation of time(MT) is the difference between mean solar time (MST) and true solar time (UTS):
SW = CNE - WIS
This difference at any particular moment of time is the same for an observer at any point on the Earth.
Assignment for discussion with the teacher (possible on or in the video room)
The true day is the time during which the Sun makes a complete circle in the sky, during the year it ranges from 23 hours 44 minutes to 24 hours 14 minutes, depending on the time of year. The present orbit of the Earth intersects with a circular one only four times a year: April 16 , June 14 , September 1 and December 25. These days, the equation of time is 0. Accordingly, each season has its own maximum equation of time: about 12th of February+ 14.3 min, May 15- 3.8 min, July 27+ 6.4 min and November 4- 16.4 min. Explain why the equation of time is 0 on days when the Earth's orbit intersects the circular one.
For definiteness of theoretical calculations, it is accepted ephemeris (tabular) a second equal to the mean solar second on January 01, 1900 at 12 o'clock equal 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 - a change in the lunar phases. Phase F celestial body (Moon, planets, etc.) is determined by the ratio of the largest width of the illuminated part of the disk d to its diameter D:
Line terminator separates the dark and light parts of the luminary's disk.
The moon moves around the earth in the same direction in which the earth rotates around its axis: from west to east. The display of this movement is the apparent movement of the Moon against the background of the stars towards the rotation of the sky. Every day, the Moon moves east 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) lunarmonth- the period of time during which the moon makes one complete revolution around the earth relative to the fixed stars. Equals 27 days 07 h 43 min 11.51 s.
Synodic (calendar) lunarmonth- the time interval between two successive phases of the same name (usually new moons) of the Moon, equal to 29 days 12 hours 44 minutes 2.78 seconds.
The totality of the phenomena of the visible movement of the Moon against the background of stars and the change in the phases of the Moon makes it possible to navigate the Moon on the ground. The moon appears with a narrow crescent in the west and disappears in the rays of the morning dawn with the same narrow crescent in the east. If we mentally attach a straight line to the left of the crescent moon, then we can read either the letter “P” (growing) in the sky, while the “horns” of the month are turned to the left - the month is visible in the west; or the letter "C" (getting old), while 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.
The surface of the Earth is divided into 24 areas, bounded by meridians, - time zones. The zero time zone is located symmetrically with respect to the Greenwich (zero) 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 1 hour apart, so when moving from one time zone to another, time changes by an integer number of hours, and the number of minutes and seconds does not change. New calendar days (and New Year) begin on date lines (demarcation line), passing mainly along the meridian of longitude 180 east near the northeastern border of the Russian Federation. To the west of the date line, the day of the month is always one more than to the east of it. When crossing this line from west to east, the calendar number decreases per unit, and when crossing the line from east to west, the calendar number increases per unit. This eliminates the error in counting time when traveling around the world, as well as moving from the Eastern Hemisphere of the Earth to the Western.
Daylight saving time- standard time, changed to an integer number of hours by government decree. For Russia, it is equal to standard time, plus 1 hour.
Moscow time- daylight saving time of the second time zone (plus 1 hour): Tm = T0 + 3 (hours).
Summer time- standard standard time, which is changed by an additional plus 1 hour by government order for the period of summer time in order to save energy resources.
Due to the rotation of the Earth, the difference between the moments of the onset of noon or the culmination of stars with known equatorial coordinates at 2 points is equal to the difference in the geographical longitudes of the 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 .
Geographic longitude area is counted to the east of the "zero" (Greenwich) meridian and is numerically equal to the time interval between the climaxes of the same name of the same luminary on the Greenwich meridian and at the observation point:
where S- sidereal time at a point with a given geographical latitude, S0- sidereal time at the zero meridian. Expressed in degrees or hours, minutes and seconds.
To determine the geographic longitude of the area, it is necessary to determine the moment of climax of any luminary (usually the Sun) with known equatorial coordinates. By translating with the help of special tables or a calculator the time of observations from the mean solar to the stellar, and also knowing the time of the culmination of this luminary on the Greenwich meridian from the reference book, one can determine the longitude of the area. To determine the moment of climax, it is enough to determine the height (zenith distance) of the luminary at any precisely fixed moment in time.
Assignments for discussion with the teacher (possible on or in the video room)
Why is solar time used in everyday life and not sidereal time?
Is it possible to construct a sundial that would show the mean solar time, maternity, summer, etc.? Prepare reasoned answers, discuss answers with the teacher.
Instruments for measuring and storing time
Even in ancient Babylon, the solar day was divided into 24 hours (360: 24 = 15). Later, each hour was divided into 60 minutes, and each minute into 60 seconds.
The first instruments for measuring time were sundials. The simplest sundial was gnomon- a vertical pole in the center of a horizontal platform with divisions. The shadow from the gnomon describes a complex curve that depends on the height of the Sun and changes from day to day depending on the position of the Sun on the ecliptic, the speed of the shadow also changes. Look at the pictures: the angles corresponding to each hour have a different value.
The accuracy of measuring time with the help of a gnomon was determined by its height: the higher the gnomon, the longer the shadow cast by it, which increased the accuracy of the measurement. For ease of reference, there was a hole at the end of the gnomon, which was clearly visible in the shadow. It was possible to increase the accuracy of time measurement by finding the bisector of the morning and evening shadows of the same length: at dawn and dusk, the rate of change in the length of the shadow is higher and its direction (for a given length) is set more accurately.
By tilting the platform so that the pole from the gnomon is aimed at the celestial pole, we get an equatorial sundial in which the speed of the shadow is uniform.
To measure time at night and in bad weather, hourglasses, fire and water clocks were invented.
Hourglass have a simple design, can be used at any time of the day and regardless of the weather, they are accurate, but bulky and “start up” only for a short time.
fire clock represent a spiral or a stick from a combustible substance with applied divisions. The disadvantages of these watches: low precision (dependence of the burning rate on the composition of the substance and the weather) and the complexity of manufacturing.
It is interesting
In ancient China, special mixtures were created that could burn for a long time (for months) and did not require constant monitoring.
Ancient miners used a fire clock, representing a clay vessel with oil, which was enough for 10 hours of lamp burning. The miner finished his work when the oil burned out.
water clock used in many countries of the ancient world.
Mechanical watches with weights and wheels were first invented in the X-XI centuries. In Russia, the first tower mechanical watches set by the monk Lazar Serb in the Moscow Kremlin in 1404. pendulum clock invented in 1657 by the Dutch physicist and astronomer H. Huygens.
It is interesting
Take a trip back in time with Ronald Top, watch the video clip “Time. The history of watch creation. History of inventions.
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The calendar . Basic calendars
| Ancient Egyptian calendar in Senenmut's tomb |
The calendar- a continuous number system for long periods of time, based on the periodicity of natural phenomena, which is especially clearly manifested in celestial phenomena (the movement of celestial bodies). The entire centuries-old history of human culture is inextricably linked with the calendar. The need for calendars arose in such extreme antiquity, when people could not yet read and write. The calendars determined the onset of spring, summer, autumn and winter, the periods of flowering plants, fruit ripening, the collection of medicinal herbs, changes in the behavior and life of animals, weather changes, the time of agricultural work, and much more. As in ancient times, at present, calendars allow you to regulate and plan the life and economic activities of people. |
There are three main types of calendars: lunar, solar, lunisolar.
1. Lunar calendar. It originated over 30,000 years ago. This calendar is based on a synodic lunar month of 29.5 mean solar day. The lunar year of the calendar contains 354 (355) days (11.25 days shorter than the solar year) and is divided into 12 months: each odd month has 30 days, and the even month has 29 days. Since the calendar month is 0.0306 days shorter than the synodic month, in 30 years the difference between them reaches 11 days. There are two cycles: 30-year-old Arabic (11/30) and 8-year-old Turkish (8/3). In the Arabic 30-year cycle, there are 19 "simple" years of 354 days and 11 "leap years" of 355 days. In the Turkish 8-year cycle, there are 5 "simple" and 3 "leap" years. The lunar calendar is accepted as a religious and state calendar in many Muslim countries.
2. Solar calendar. The solar calendar is based on the tropical year (periods of the seasons). Appearing over 6000 years ago in ancient Egypt, this calendar is currently accepted as the world calendar.
Julian the solar calendar of the "old style" contains 365.25 days: three "simple" years have 365 days each, one leap year - 366 days. There are 12 months of 30 and 31 days each in a year (except February). The Julian year is 11 minutes 13.9 seconds behind the tropical year. For 1500 years of its application, an error of 10 days has accumulated.
V Gregorian In the New Style solar calendar, the length of the year is 365.242500 days. Differences from the Julian solar calendar: the count of days was moved 10 days ahead; new centuries and millennia begin on January 1 of the "first" year of the given century and millennium; Every century that is not divisible by 4 without a remainder is not considered a leap year. This corrects an error of 3 days for every 400 years.
In our country, before the revolution, the Julian calendar of the “old style” was used, the error of which by 1917 was 13 days. In 1918, the world-famous Gregorian calendar of the "new style" was introduced in the country and all dates were shifted 13 days ahead.
For the curious
Watch an educational cartoon about the history of the Julian and Gregorian calendars.
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The formula for converting dates from the Julian calendar to the Gregorian:
where
T G and T Yu- dates according to the Gregorian and Julian calendars;
n is an integer number of days WITH- the number of complete past centuries;
From 1 is the nearest number of centuries, a multiple of four.
Consider other examples of varieties of solar calendars.
Persian calendar. Designed by Omar Khayyam in 1079; was used on the territory of Persia and a number of other states until the middle of the 19th century. The duration of the tropical year is 365.24242 days; The 33-year cycle includes 25 "simple" and 8 "leap" years. Much more accurate than the Gregorian one: an error of 1 year "runs" in 4500 years.
Coptic (Alexandrian) calendar: in a year - 12 months of 30 days; after 12 months in a "simple" year, 5 are added, in a "leap" year - 6 extra days. Used in the territory of the Copts (Ethiopia, Egypt, Sudan, Turkey, etc.).
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3. Lunisolar calendar. It arose at the beginning of the 1st millennium BC, was used in Ancient China, India, Babylon, Judea, Ancient Greece and Rome. It is based on the movement of the Moon, coordinated with the annual movement of the Sun. The year consists of 12 lunar months of 29 and 30 days each, to which "leap" years are periodically added to take into account the movement of the Sun, containing an additional 13th month: "simple" years last 353, 354, 355 days, and "leap years" » - 383, 384 or 385 days. Currently the official calendar in Israel (the beginning of the year falls on different days between September 6 and October 5). It is also used along with the state - the Gregorian calendar, in the countries of Southeast Asia (Vietnam, China, etc.). |
lunisolar calendar |
In addition to the main types of calendars described, different peoples created other calendars, for example, the Eastern, the Mayan calendar, the Aztec calendar, Hindu calendars, etc.
By the beginning of the 20th century, the growth of international scientific, technical, cultural and economic ties necessitated the creation of a single, simple and accurate World Calendar. Existing calendars have a number of shortcomings: insufficient correspondence between the duration of the tropical year and the dates of astronomical phenomena associated with the movement of the Sun in the celestial sphere; unequal and changeable length of months; inconsistency of the numbers of the month and days of the week, inconsistencies in their names with the position in the calendar, etc. Various projects were considered, one of which in 1954 was recommended for consideration by the UN General Assembly. However, for religious reasons, the project was not implemented. The introduction of a single world perpetual calendar remains one of the problems of our time.
