Saturday gives us an extra day. February 29th means it's a Leap Year. Do you know why we get the 366th day every four years?
In short, sun and moon cycles need to be synced up with the Earth's rotation every once in a while. Julius Ceasar consulted mathematicians and philosophers to establish the extra day every four years. The Julian calendar was replaced with the Gregorian calendar in the 1500s. In 1582, Pope Gregory XIII also consulted with astronomers, mathematicians, and religious people to put us on the path we are on now. Years that are divisible by 4 get leap years.
Every three out of four turns of the century do not get leap years. Meaning, we got one in 2000 but will not have one in 2100, 2200 or 2300. Mind blown.