Why leap day is really about party planning

CLOCKS and calendars are handy, even if they are out of step with the astronomical world.

Earth’s actual orbit around the sun takes six hours and nine minutes more than the strict 365 days that our regular scheduling mechanisms prefer. To sync the natural world to our calendars, we add a leap day every four years, on Feb 29 – Thursday.

This all seems like mere chronological housekeeping, but there are other concerns at play, according to Judah Levine. He is the head of the Network Synchronization Project in the Time and Frequency Division at the National Institute of Standards and Technology, or NIST, in Boulder, Colorado.