ce when the sun is directly over the Earth's equator. To make up for this .2422 day difference, we add an extra day (a "Leap Day") to the calendar in certain years.

Which years are considered Leap Years? Most of us think Leap Years happen every 4 years. But there's more to it. In the Gregorian calendar unveiled by Pope Gregory XIII in 1582 A.D. that we use today, a Leap Year is any year divisible by 4; however, if the year is divisible by 100, it is not a Leap Year; but, if the year is divisible by 400, it IS a Leap Year. So year 2100 will NOT be a Leap Year (not that I'll care at age 136), while 2000 indeed was a Leap Year.

Leap Year rules were simpler during the 16 centuries that Julius Caesar's Julian calendar was used (beginning 45 BC). The rule was to add a Leap Day every 4 years. Problem was, this did not match the vernal equinox cycle with enough precision.

Why is it called a Leap Year? One theory is that a