February 29 takes approximately 6 hours longer than 365 whole days. A leap day compensates for this lag, realigning the calendar with the Earth's position in the Solar System; otherwise, seasons would occur later than intended in the calendar year. The Julian calendar used in Christendom until the 16th century added a leap day every four years; but this rule adds too many days (roughly 3 every 400 years), making the equinoxes and solstices shift gradually to earlier dates. By the 16th century the vernal equinox had drifted to March 11, and the Gregorian calendar was introduced both to shift it back
Decimal calendar Decimal calendar A decimal calendar is a calendar which includes units of time based on the decimal system. The original Roman calendar consisted of ten months (however, the calendar year only lasted 304 days, with 61 days during winter not assigned to any month). The months of Ianuarius and Februarius were added to the calendar by Numa Pompilius in 700 BC. The ancient Egyptian calendar consisted of twelve months, each divided into three weeks of ten days, with five intercalary days. The French Republican Calendar was introduced (along with decimal time) in 1793, and was similar to the ancient Egyptian