ELI5: Explain Like I'm 5

Intercalation (timekeeping)

Okay kiddo, so intercalation is a way of keeping track of time that makes sure our calendars match up with the seasons. You know how we have different seasons like summer and winter? Well, they happen because the Earth is tilted and rotates around the sun at a certain angle.

This rotation takes a little bit over 365 days to complete, which is why we usually have 365 days in a year. But sometimes, the Earth's rotation slows down or speeds up a little bit, which can make the seasons not match up with our calendars anymore. So we need to add or subtract some days from our calendar to make up for the difference.

This is where intercalation comes in. Basically, we add or subtract extra days to a year or month to make sure that our calendars and the seasons stay in sync. Some calendars use leap years, like adding one extra day to February every four years, while others use different methods like adding extra months.

So, in summary, intercalation is a way of making sure our calendars and the actual year match up so that we can always know what season it is and celebrate holidays at the right time.