Solar CalendarsRomans began the year in March, near the spring equinox. Julius Caesar adopted a year of 365 days with 366 every fourth (leap) year. The prior Roman calendar was much like the present Jewish one. With the Julian calendar, the average year = 365.25 days, a bit too long. Error amounts to a day every 128 years. In the fourth century the Council of Nicaea decided that the spring equinox should occur on March 21. By the 16th century it was beginning March 11. Pope Gregory imposed the Gregorian calendar in 1582:Same as Julian, but years divisible by 100 are not leap years unless also divisible by 400. Thus 1700, 1800, and 1900 were not leap years, 2000 was a leap year. An excellent solar calendar: Average year = 365 + 1/4 – 3/400 = 365.2425 days Error will amount to 1 day after 3300 years. but it ignores the moon. If you know that an event occurred on Sept 7, . . .
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