July 4, December 24, January 1, and December 25 are the least common birthdays, in order of decreasing popularity. Halloween, October 31, is also among the ten least common birthday dates. Late November, around when Thanksgiving usually falls, seems to be an unpopular time to have a baby, as well.

Who Invented Leap Year?

Julius Caesar Leap days were first added to the Julian Calendar in 46 B.C. by Julius Caesar at the advice of Sosigenes, an Alexandrian astronomer. Celebrating the leap year? Take a moment to thank Christopher Clavius (1538-1612).