Girlawhirl learned a leap year – or intercalary year – goes back to none other than Julius Caesar. Back in 45BC the Roman Emperor created a 12-month, 365-day year calendar, including an extra day every fourth February. But it wasn’t precise – in reality it was too long by 11 minutes and 14 seconds.
By the 16th Century,
the Spring Solstice on the calendar was actually 10 days too soon. So Pope Gregory XIII decided to create a new calendar, the one still used today. Pope Gregory adjusted the date of the Spring Solstice by 11 days and added a new rule for leap years. Under the new calendar, a century year is only a leap year if it is divisible by 400. For example, 2000 was a leap year, but 1900 wasn’t, and 2100 won’t be. 
Under the Gregorian calendar, it will take 3,000 years before a day is gained in error.
Click here to visit infoplease.com for more information on leap years.