Читать книгу Biblical Chronology - Valeriy Sterkh - Страница 15

Historians and annalists often deal with calendar calculations which involve various types of dates. To simplify the process for converting dates from one calendar to another, the “system of Julian days” or “continuous day count” was introduced. In 1583, the French scholar Joseph Justus Scaliger (1540 – 1609) came up with the idea of the so-called “Julian period”. He named this method of calculation in honor of his father Julius Caesar Scaliger (1484 – 1558), the famous humanist and scholar.

Joseph Scaliger suggested a chronological scale against which any historical date could be aligned. The starting point for counting the “Julian days” (JDN=0) was set to January 1, 4713 BNE, which was the era “from the foundation of the world” according to Scaliger. Then, the JDN value would increase by one every day. So, January 2, 4713 BNE equals to JDN=1 and so on. For example, January 1 of the 1st year NE is JDN=1721424.

In 1849, John Herschel (1792 – 1871) suggested expressing all the dates though the JD value, which is the number of days that passed since the beginning of the Scaliger cycle. The difference between the Julian date (JD) and the Julian day number (JDN) is that the former contains a fractional part which indicates the time of 24-hour day. It was agreed that the beginning of the Julian day would be noontime according to Greenwich Mean Time. So, the midnight of January 1 of the 1st year NE corresponds to JD=1721423.5. Note that the JD=1721424 will accumulate only by the noon of the specified day, because the count was started at noon January 1, 4713 BNE (the “zero point”). To make our calculations easier, we will use the rounded value of the Julian date or the Julian day number (JDN).

The procedure for calculating the Julian day number (JDN) for a specific Julian calendar date is as follows:

1) a= [(14-month) /12].

2) y=year+4800-a.

3) m=month+12a-3.

4) Julian day number:

JDN=day+ [(153m+2) /5] +365y+ [y/4] -32083.

Where “year” is the year of NE; “month” is the number of the month; “day” is the day of the month; value in brackets is the integer part.

Knowing the JDN, you can find the day of the week by calculating the remainder of the division of JDN by 7. Based on the remainder value, the days of the week are distributed as follows: 0 – Monday, 1 – Tuesday, 2 – Wednesday, 3 – Thursday, 4 – Friday, 5 – Saturday, 6 – Sunday.

For example, let us calculate the Julian day number for the Jewish Passover in 2016 (April 10 in the Julian calendar):

1) a=0.

2) y=6816.

3) m=1.

4) JDN=2457502.

Remainder of division (JDN mod 7) =5, therefore, it is Saturday.