On 1 January 45 BC, by edict, Julius Caesar reformed the historic Roman calendar to make it a consistent solar calendar (rather than one which was neither strictly lunar nor strictly solar), thus removing the need … See more

In the Gregorian calendar, the standard calendar in most of the world, most years that are multiples of 4 are leap years. In each leap year, the month of February has 29 days instead of … See more

The Revised Julian calendar adds an extra day to February in years that are multiples of four, except for years that are multiples of 100 that do not leave a remainder of 200 or 600 when … See more

The Hebrew calendar is lunisolar with an embolismic month. This extra month is called Adar Rishon (first Adar) and is added before See more

The Julian calendar was instituted in 45 BC at the order of Julius Caesar, and the original intent was to make every fourth year a leap year, but this was not carried out correctly. See more

The Chinese calendar is lunisolar, so a leap year has an extra month, often called an embolismic month after the Greek word for it. In the Chinese … See more

The observed and calculated versions of the Islamic calendar do not have regular leap days, even though both have lunar months containing 29 or 30 days, generally in … See more