Calendar Systems

This article was inspired by Xidnaf's rant about calendars^[►]

Solar and Lunar Calendars

Egyptian Calendar: Ancient Egypt used a 12 month calendar. Each month had 30 days, for a total of 360 days. The remaining 5 days of the year were included "outside" of the months. Because every month was 30 days, they could be divided into 10 day periods, which acted as weeks.

Julian Calendar: If the Egyptian calendar included leap years and the extra days were added to months, you'd get the Julian Calendar. The 12 months were The five intercalary days were moved to certain months: January, March, May, July, August, October, and December each got 31 days; February was left with 28 days, but on every fourth year, it had 29 days to catch up with the seasons.

Gregorian Calendar: The improved version of the Julian Calendar, the Gregorian added extra rules for leap years to make it more accurate: every 100 years didn't get a leap year, except every 400 years which have a leap year.

Hijri Calendar: The Islamic Calendar has 12 lunar months, which run from new moon to new moon. Because intercalary days were forbidden, each year is only 354 or 355 days. Because it doesn't align with the seasons, some countries use a solar calendar for that purpose. The 9th month of Ramadan is when Muslims are obligated to fast from sunrise to sunset. The length of sunlight when Ramadan takes place varies more the further you are from the Equator, meaning it can be from short winters to long summers.

Badíʻ calendar: The calendar used by Baháʼís, this calendar has 19 days per month and 19 months per year, for a total of 361 days. The remaining 4 days of the year, called "Ayyám-i-Há," are in between the 18th and 19th months: Mulk and ʻAláʼ respectively. The final month ends at the Spring Equinox.

Lunisolar Calendars

• Jewish Calendar
• Chinese Calendar