Why do We Have Leap Day?

Today is Leap Day, that extra day in February that occurs every four years. But how and why did it get it's start? Here are the facts and some interesting tidbits of info about leap day.

Who started leap year?

Julius Caesar and Pope Gregory XIII

Why did they want it?

Julius Caesar didn't like the Roman calendar. It alternated between 355 days and 377 days every year. Basically every other year, there was extra month between February and March. Caesar worked with the astronomer Sosigenes and came up with the Julian calendar, adding Leap Day every four years in 45 BC. But, Pope Gregory XIII wanted Easter in the spring. The Julian calendar had too many Leap Days and Easter was moving to a different time of year. So in 1582, the Gregorian calendar was introduced, which took out three Leap Days every 400 years. The new calender lined up with the lunar calendar, also. It is now the dominate calendar throughout the world. On a side note, Augustus Caesar is responsible for February being so short. Months in the Julian calendar were 30 or 31 days. In 8 BC, Augustus didn’t like the month that was named for him, August, being shorter than the month named for Julius, July, so he stole a day from February to make them the same length. National Geographic

Does leap day happen every four years?

Actually, no. Here's how it works. The Earth orbits the sun every 365.2422 days. Extra days are needed in certain years or our seasons would get out of sync. If we added a day every five years, it wouldn't be enough, and adding one every four years is too much. So, every four years a day is added except in years divisible by 100, like 1800, 1900, 2000, 2100, etc. But, if divisible by 400, like 1600, 2000, 2400 and 2800, there will be a Leap Day. But years 1700, 1800, 1900, 2100, 2200, 2300 won’t. Wikipedia