Astronomical account of years and days
In the XVIII century.the era introduced by Dionysius was expanded to account for years before the "birth of Christ"( a D.-ante Deum - "to the Lord").It was assumed that the first year BC.e.directly adjacent to the 1st year of n.e. It was also assumed that the number of years BC.e.increases with the distance to the past, however, the months, the numbers in them, and the days of the week are counted henceforth, just as in the years n.e. Consequently, the boundary between the 1st year BC.e.and 1 st year n.e.is the "moment" that divides December 31, 1 BC.e.and on 1 January, 1 n.e. Leap years are those years BC.the number of which, when divided by 4, gives in the remainder 1: 9th, 13th, etc. This years account is called historical or chronological. The absence of a "zero year" often leads to errors in the calculation of the time interval between two events, one of which occurred before, the other after the beginning of the count of years after AD.e. For example, in 1937 in Italy and Germany, the 2000th anniversary of the birth of Emperor Augustus was celebrated. Meanwhile Augustus was born in 63 BC.E., therefore, by the 1st year of AD.e.he turned 62( not 63) years, and the 2000th anniversary of this event took place in 1938. Similarly, in 1945 instead of 1946 in our country was celebrated the 2000 anniversary of the death of the outstanding ancient Roman poet and philosopher Lucretius, whodied in 55 BC.e.
The Cassini rule. Defining the moments of the onset of solar and lunar eclipses, the appearance of comets, etc., astronomers developed their own astronomical account system, which was first used in 1740 by the French scientist Jacques Cassini( 1677-1756) in two of his works: "Elements of Astronomy"and "Astronomical tables."It was a year before the 1st year of AD.e., called zero, preceding the zero-minus first( Fig.):
Fig. Two ways of counting the years - historical and astronomical
| Astronomical account years | Historical account years |
| 0 year zero minus 1 year minus 2 year | 1st G. TO N. 9. 2nd G. ยป 3" |
So came the" rule Cassini ": to determine the length of time between two events, divided by the era of our era, the year BC.e.when subtracting it is necessary to reduce by one.
Thus, 63 BC.e.this is "minus 62 years", so the period of time that separates 63 g. to the point of e.and in 1937, Mr. .is equal to: 1937 -( - 62) = 1937 + 62 = 1999. The same is true in the second case: 1945 -( -54) = 1999.
And in the astronomical account of years and months, as in positiveyears, are considered forward. For example, astronomers have determined that Halley's comet was visible in the sky in -1161.3 g. Let's translate this date into historical calculation. First of all, 0.3 years is 0.7 of the previous year, "minus 1162" years, with 0.7 years corresponding to the date close to September 14.In turn, the "minus 1162" year is 1163 BC.e. Consequently, - 1161.3 = September 14 minus 1162 years = September 14, 1163 BC.e.
System of Julian days. Both astronomical and chronological calculations often use a continuous count of days, beginning on January 1, 4713 BC.e. This so-called Julian period was introduced in 1583 by the French scientist Joseph Scaliger( 1540-1609).For the beginning of the Julian date, the midday on the zero( Greenwich) meridian is accepted. In the system of the Julian days, the day is counted from the average Greenwich midday following the midnight Greenwich midnight, which determines the beginning of the calendar date under consideration. The Julian days are abbreviated as JD or Yu. D. and are indicated today in all astronomical calendars. Thus, on January 1, 1980, there are 2,444,240 days of the Julian period, as of January 1, 1981, 2,444,606 JD, etc. The Christian era( January 1, 1 century) corresponds to 1,721,058 JD, the Diocletian era( August 29, 284 CE) - 1 825030 JD.The Julian period is very convenient for various calculations, and it is often used in astronomy. The German astronomer, prominent Christian historian Christian-Ludwik Idler( 1766-1846), spoke well of the role of this account system in chronology: "It can rightfully be said that only with the introduction of the Julian period did the light and order come in chronology."
Table of Julian days for the period from 4700 BC.e.to 2200 g.e.attaching. Using it, it should be remembered that in the table all Julian days are given on the zero January of the corresponding year, i.e. on December 31,5 of the previous calendar year, that their account is kept from the average Greenwich midday and that the years account should be astronomical,the number of the year BC.e.should be reduced by one.
Example. Determine the Julian day March 26, 1986
From table A we find: 1900 - 2 415 019
From table B: 86 31 412
From table C: March 26 85
Summing up, we get 2 446 516
Thus, at noon on March 261986, the 2,446,516th day of the Julian period will begin.
The following remark is also relevant. In Table. B the correction for the beginning of the year is 366 days in a leap year. But in the Gregorian calendar, the centennial year in three cases out of four is simple, and to use the same table of corrections for the year( Table B) for both calendars, in Table. And for simple centuries( 1700, 1800, 1900), the number of the Julian day is reduced by one, that is, it is indicated not on 31.5, but on 30.5 December. Therefore, when calculating the Julian day for any number of a simple century, to the number of Table. A should be added one, and then the corresponding date the number of tables. B.
However, the Julian day number JD at the moment of January 0.5 for any year R of the Gregorian calendar can be determined by the following formula:
JD =( 4712 + R) * 365.25 + [R / 400] - [R / 100] + K,
where the numerical value of K is 1, 1.75, 1.50 and 1.25 if R is a leap year or the 1st, 2nd and 3rd after the nearest preceding leap year.
So, for 1986, we have [1986/400] = 4, [1986/100] = 19 and K = 1.5.Therefore, JD =( 4712 + 1986) * 365.25 + 4 - 19 + 1.5 = 2 446 431, ie, at noon on December 31, 1985( or January, 0.5 1986), there were started 2 446 431day of the Julian period.