The Roman CalendarWe took our calendar from the Romans. Very early in their history, the Romans began basing their calendar on the idea that 12 lunar months make a year. Each lunar month (from new moon to new moon) is about 29 1/2 days, so the Roman year came to 354 days. But the true solar year (the time it takes the earth to circle the sun) is just under 65 1/4 days. The Romans made up for the difference by adding an extra month every few years.
When Julius Caesar ruled Rome, he found that the calendar was wrong by 80 days. The calendar said it was spring but the season was really midwinter. Caesar ordered that each year should be 365 days, with an extra day added in February every 4th year (leap year) to make the calendar come out right. Leap years would always be divisible by 4. Caesar also gave up the lunar month and set a month's length at 30 or 31 days. Only February remained less than 30 days long.
MONTHS OF THE PRINCIPAL CALENDARS
GREGORIAN CALENDAR
name........................days
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January.....................31
begins 10 days after
the winter solstice
February....................28
in leap years...............29
March........................31
April..........................30
May...........................31
June...........................30
July............................31
August.......................31
September.................30
October.....................31
November..................30
December...................31
JEWISH CALENDAR
Name........................days
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Abib or Nisan.........29 or 30
Iyar.........................29 or 30
Sivan.......................29 or 30
Tammuz...................29 or 30
Ab...........................29 or 30
Tishri........................29 or 30
Heshvan....................29 or 30
Kislev.......................29 or 30
Tebet........................29 or 30
Shebat.......................29 or 30
Adar..........................29 or 30
An extra month is added about
every three years,called Adar2
MUHAMMADAN CALENDAR
name........................days
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Muharram....................30
in A.H. 1392 began
Feb. 16, 1972
Safar............................29
Rabi I...........................30
Rabi II..........................29
Jumada II......................29
Rajab............................30
Sha'ban.........................29
Ramadan.......................30
Shawwal........................29
Dhu'l-Qa'dah.................30
Dhu'l-Hija......................29
in leap years...................30
The equinoxes occur on Spring [March 21] & Fall [September 23].
The solstices occur on Summer [June 22] & Winter [December 22].
The Roman Calendar.
Pope Gregory Changes the Calendar
But there was still a small mistake in the Julian Calendar. The sun's year is really 11 minutes and 14 seconds shorter than the 365 1/4 day year recommended by Sosigenes. In 1600 years this added up to 10 days, so that the vernal equinox, the 1st day of spring(when the sun has reached the celestial equator and day and night are equal in length), occurred earlier and earlier. By 1582 it fell on March 11 instead of March 21. Pope Gregory XIII took the advice of the astronomer Christopher Clavius. He corrected the mistake by dropping 10 days, so that the day after October 4, 1582 was October 15, to keep this from happening again, he decreed that century years (the 1st year to each century); even though divisible by 4, should not have the extra day in February unless they could be divided by 400. Thus, A.D. 1900 was not a leap year,but A.D. 2000 will be.
Catholic countries adopted the Gregorian Calender (named for Pope Gregory), but Protestant and Greek Orthodox countries did not. One hundred and seventy years later England and her American colonies found that their calendar had slipped away from the sun's time by 11 days. They dropped these days in 1752, adopting the Gregorian calendar. Thus Washington's birthday is February 22 (New Style), but he was really born on February 11 (Old Style). Russia did not change its calendar until 1912, and Romania not until 1924. That is why you may see 2 different dates given for some historical events.
People are still trying to reform the calendar, but so far we continue to use the Roman calendar as it was improved by Pope Gregory XIII.
(Reviewed by Catharine Barry
American Museum of Natural History)
