Our actual calendar "Gregorian" had been established by Pope Gregoire XIII in the 16th century. It is an improvement of an older calendar established in 708 Rome's year by Julius Caesar. Julius Caesar decided that the Roman calendar did not have to take in account the Moon motion, but only the Sun motion. The old roman year, "Romulus year" had got 10 months and had been changed in a 12-month year. September was before this change the seventh month, October eighth month, November the ninth month and December the tenth one. With the Julius Caesar reform, the beginning of the year became January 1 instead of March 1 and the length of the year was 365.25 days rounded to 365 days. One day is added each four year to get back the 0.25 day lost each year.
The trouble is that this calendar is not precise enough. There
is a loss of 0.078 days per year, which give 3 days each 400 years.
That's why Pope Gregoire XIII had to do a new reform.
Thursday, October 4 1582, was followed by Friday
October 15 1582.
It had also been decided to remove the day normally added to secular
years (1600, 1700, 1800...) except for secular year that can be divided
by 400. That is why 1700, 1800, 1900 were not leap years when 2000 will
be one. Julian calendar reform had been applied in different ways,
depending on the country.
For the United States, the Gregorian calendar (new style) applies from 9/14/1752. Eleven days were added to the Julian (old style) date 9/2/1752.
Example:
Suppose you want the horoscope of George Washington. He was born
2/11/1731 (old style). You must give to Proastro 2/22/1731 (new style)
because this date is after 10/4/1582.
To translate Julian date to Gregorian date, use the following table:
Julian date (old style) |
what to add to get Gregorian date (new style) |
From 10/5/1582 to end February 1700 |
+ 10 days |
From 3/1/1700 to end February 1800 |
+ 11 days |
From 3/1/1800 to end February 1900 |
+ 12 days |
From 3/1/1900 |
+ 13 days |
Exact Formula:
if month is 1 (January) or 2 (February)
let y = year -1 else y = year.
Correction is then A - Ent(A/4)- 2
Where
A = Ent(y/100).
and
Ent(x) is the number rounded to integer.
Ent(4.18) = 4
Ent(-4.18) = -4
Year before 1 is year zero, and year before zero is -1. For
historians, year zero is year one before Christ, year -1 is year two
before Christ and so on... (See table below).
You must give Proastro only astronomical years.
-4 |
-3 |
-2 |
-1 |
0 |
1 |
2 |
3 |
4 |
astronomical way |
5 B.C. |
4 B.C. |
3 B.C. |
2 B.C. |
1 B.C. |
1 A.C. |
2 A.C. |
3 A.C. |
4 A.C. |
historians way |
B.C. Before Christ
A.C. After Christ