Why Mars Needs Leap Days, Too

Alien civilizations on other worlds would need much more awkward contortions to their calendars than we make here on Earth

This Saturday, you have the gift of time. Feb. 29 is a leap day — a calendar oddity that gives us an extra day.

You probably know why: The time it takes Earth to rotate on its axis is called a day — but it doesn’t take an even number of days to complete a single loop around the sun, or one orbit. Instead it takes a messy 365.2422 spins. And yet the calendar year runs out after 365 days. That means that when the clock strikes midnight on New Year’s Eve, Earth hasn’t quite circled all the way back to