The leap year is needed because Earth does not go around the Sun in exactly 365 days, but in 365. 2422 days To keep the seasons in the same part of the year. The leap year is needed because Earth does not go around the Sun in exactly 365 days, but in 365. 2422 days To keep the seasons in the same part of the year we need that occasional leap day. The ancient Egyptians had a 365 day calendar and the seasons floated through the year over a cycle of about 1400 years. Given that Egypt s seasons tend to be hot and dry versus hot and wet, it did not make a lot of difference to them, but for Europeans with pronounced seasons it mattered. Thus ancient Rome adopted the Julian calendar (paid and promoted by Julius Caesar, designed by a Greek astronomer for Alexandria named Sosigenes).
It had a leap day every fourth year, thus assuming a year exactly 365. 25 days long. This small error began to accumulate, moving the first day of spring from March 25 to March 11 by the early 1500s. The problem this created was that it moved Ash Wednesday and the start of Lent ever earlier, and clearly the day would come when Christmas would occur during Lent. The Church viewed this as a problem and called a conference which ultimately adopted the current Gregorian calendar, moving the start of spring back to March 20 or 21. Now century years are leap years only if divisible by 400 (not 1900 or 2100, but 2000 was).
The Earth takes 365. 24 days to make one orbit around the Sun. The Earth is tilted and stays tilted in the same direction as it moves, so the north and south.
The Earth takes 365. 24 days to make one orbit around the Sun. The Earth is tilted and stays tilted in the same direction as it moves, so the north and south get different amounts of sunlight depending on where Earth is in its orbit. Thus, the seasons have a 365. 24 day long cycle. This is a completely separate astronomical fact from the 1 day that the Earth takes to spin around its axis. With the result that the year isn t a whole number of days. We could have a leap 0. 24 days, and make January 1 (and all other days) start at 6am. And then start at noon for the next year. We don t want to do that. If we only had 365-day years, the summer solstice would drift from June 20 to June 21 to June 22 and eventually into July, August, September.
That s what was happening in Rome before Julius Caesar standardized the calendar. So we break each 4-year cycle into calendar years of 365, 365, 365, and 366 days. Some years the summer solstice is June 20 and some it s June 21, but never July. Caesar s calendar got the average year to 365. 25 days, which is close enough to the solar year that the seasons only drifted by 1 day every hundred years. There are some additional tweaks (ie, skip having a leap year every hundredth year) to make the modern calendar even more accurate. So why February? Because the Roman calendar originally started with March, making the end of February the end of the year.