Leap Day and Leap Year
Earth travels around the sun about 1 ° / day. But we are actually short of a full orbit by about ¼ ° every year. So every 4th year, a Leap Year, we add a day to the calendar, to allow earth to get back to where she’s supposed to be… a Leap Day!
Leap Second
At the same time of course, earth is rotating. The Earth is approximately 24,000 miles around at the equator. She rotates once every 24 hours, so that’s about 1,000 miles / hour. That’s equal to approximately 16.6 miles / minute, 0.27 miles / second, or 475 yards / second. But just like an orbit is a little short after one year, a rotation is a little short after one day. So we add a Leap Second every once in a while, to let earth spin another 475 yards, into her correct position.
Of course, all of this “leap stuff” is only relevant because humans have acquired a taste for calendars, timekeeping, and punctuality. Your average raccoon couldn’t care less! He just cares if its day or night and what season it is… and he doesn’t need a human calendar to figure that out 🙂