This calendar sat on my desk through my working years. Now I keep it as a reminder. Not of the days going by, but how glad I am to be retired.
You likely know that we have leap year because our solar year is a bit longer than 365 days. In fact, the solar year is 365 days, 6 hours and 26 seconds. So every four years we add an additional day to make up for the difference. With few exceptions, years that are evenly divisible by 4 will be a leap year and have 366 days. During those years February will have 29 days, the 29th being known as "Leap Day."
The extra day every four years doesn't quite satisfy the difference between the solar year and the Gregorian calender we use. Therefore, we do not have leap year in most century years. In fact, only one in four century years has the additional leap day. The year 2000 had a leap day, but the year 1700 did not. Neither did the years 1800 or 1900. And the year 2100 will not have a leap day. A simple way to remember it is that if the century year is not evenly divisible by 400, it will not be a leap year. (Simpler still is to forget about it because one is not likely to remember two century years.)
So here's to Leap Day! Happy birthday to all those born on February 29! You have beaten the odds. (The odds for having a Leap Day birthday are 1:1,461)
As for me, I'd much rather have Leap Day in the summer. And definitely during non-election years.
*The extra day is added to February to keep the vernal equinox on or around March 21. Were the vernal equinox date changed it would affect the date of Easter.