Today is leap year day. Here's a simplified explanation of why and when we have it.
- The Earth orbits the sun every 365.2425 days.
- To make up for that .2425 day, one day is added to our calendar every 4 years.
- But one-fourth of a day does not equal .2425.
- Therefore, years which are divisible by 100 are not leap years, unless they are also divisible by 400, in which case they are leap years.
- 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not.
- 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 will not be leap years, but 2400 and 2800 will be.