We have calendars everywhere — on our phones, our watches, on the wall, at our desk and in a ridiculous number of other places. Despite the digital convenience, a huge percentage of us still have physical calendars. (That’s good as I create an art calendar each year.)

Well, all this calendar focus has piqued my interest in calendar facts and historical oddities. I’ve learned some very curious things about calendars that you probably didn’t know, either. Here are five that I found particularly weird.

1. Did you know that a full calendar cycle repeats completely every 400 years? That’s 146,097 days. After that, the sequence of ordinary and leap years repeats itself.
2. Leap days have been around a long time. Humanity learned early on that the lunar and solar phases weren’t aligned. It was the ancient Egyptians who actually determined the length of a solar year and that an extra day would have to be added every four years.
3. A seven-day week has been the norm for about 2,600 years. Credit goes to the Babylonians who created it based on phases of the moon.
4. Despite ingenious calculations, the Gregorian calendar still isn’t perfectly precise. Every 12 months, we speed ahead of the solar year by 26 seconds. So by 4909, the calendar will be ahead of solar time by one day. Not in our lifetimes, but still important minutia.
5. And on a more current note, only the U.S and Canada start the week on Sunday. For every other country in the world, Monday is the first day of the week. As it only seems to affect the visual representation of the calendar grid, I think we’re good.

I have more interesting calendar and time findings. I'll save them for another day. In the meantime, check out the 2021 Art Calendar. You KNOW you need one.