Who invented leap year? Does it pre-date the Gregorian calendar?
Innovations like that (e.g., daylight savings time) usually take time to evolve, and are adopted by fringe authorities or minor countries before becoming acceptable to the empire.
Julius Caesar invented the basics of our modern calendar in 46 BC, including the present length of months, and a leap year every four years.
In 1582 the system was modified so that century years (i.e. 1900, 2000, etc.) are only leap-years if they are evenly divisible by 400. This is the Gregorian calendar, still in use.
Arjuna34
I’ll just add to Arjuna34’s reply by noting that in England, the Gregorian calendar did not replace the Julian calendar until 1752, and Russia delayed its implementation until 1918.
Cecil’s column on leap year
ok, it was Dex’s column
I should add to what Arjuna said that Julius Caesar’s astronomer Sosigenes deserves co-credit, at least, for inventing the Julian calendar. Apparently Caesar relied heavily on Sosigenes’ advice.
Except for one small change made during Augustus’s reign. When Sextilis was renamed for him, a day was taken off of February and stuck onto August so it would have just as many days as Julius’s month. Previously, August had 30 days and February 29 (30 on leap years). The last four months were also altered to prevent three 31 day long months in a row.
According to Anthony Aveni’s “Empires of Time,” intercalation – the adding of days, months, what-have-you into a calendar to make it jibe with solar time – is a common feature of pretty much all cultures that bother (or need) to keep calendars.
Except for the Islamic calendar. It’s a lunar calendar and the Koran explicitly forbids adding an intercalary month.
As Qadgop noted before, that’s Dex’s column, but I have a small nit. It says that the astronomical year is the time it takes the earth to go exactly once around the sun, but that is not quite true. The astronomical year is 365 days, 5 hours, 48 minutes, and 46 seconds, as Dex notes, but the time it takes the earth to go exactly once around the sun is about twenty minutes longer. The astronomical year is the time from one vernal equinox to the next, which is less than the actual revolution time, because the precession of the earth’s axis causes the time of the vernal equinox to shift.