When I was a little kid I had a friend who was born on February 29, the “leap day” we add to that month every four years. I remember we used to tease him by saying that he was only three years old. I lost contact with him over the years, but I’d guess that by now he’s pretty sick of the joke.
And here we are again on the cusp of our quadrennial exercise in timekeeping: leap day 2024 is almost upon us. A handful of traditions have been associated with it; one held that this was the only acceptable day for—gasp!—women to propose marriage to men. Some folks like to treat this day as a free day that gives them time to catch up with something they’ve long been putting off.
I think that’s a pretty good idea because, after all, catching up is what leap day is all about—astronomically speaking, that is.
On supporting science journalism
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
There are two basic units of time we use that are based on astronomical events. One is the day, the length of time it takes Earth to spin once on its axis. The other is the year, the time it takes for Earth to complete an orbit of the sun. While that seems simple, these two units are actually pretty complicated. For example, Earth spins once relative to what? You need some frame of reference against which to measure that motion.
For our daily life, we use the sun. The time it takes for the sun at due south to set and then rise again and reach the southern meridian once more is one solar day, which we define as 24 hours, or 86,400 seconds. This is actually the mean solar day, which uses the center of the sun’s disk as a reference point and is an average of every day of the year. Using an average value is helpful for timekeeping because Earth moves at different speeds at different points…
Read the full article here
