GatewayRedbirds.com

We have Julius and Gregory to thank for Friday's leap day, the extra day that's periodically tacked onto the month of February.

Even before Julius Caesar's reign, the ancients had figured out that a 365-day year came closest to matching the annual round of equinoxes and solstices, which were so important for planting schedules and holy rites linked to astronomical observations. But over the years, the seasons gradually fell out of sync, and extra days had to be stuck in haphazardly to put the year back on track.

With an assist from the astronomer Sosigenes, Julius Caesar instituted the much more reliable Julian calendar, which stuck a 366th day in the month of February every four years. (OK, when the Romans started the leap-year habit in 45 B.C., they added a leap day every three years. Which was bad. But eventually they got it right.)

There was still a slight discrepancy between the calendar cycle and Earth's actual solar year, however, and by the time Gregory entered the picture in the year 1582, the difference added up to 10 days. Armed with updated astronomical advice, the pope revised the calendar again, and added an exception to the four-year leap rule. Leap days would be added to century years divisible by 400 (such as 2000), but not to the other century years (such as 1900 or 2100).

And that's where we're at right now. Even Gregory didn't completely solve the problem. There are still little discrepancies that crop up between the calendar and our planet's yearly rounds. If you could check Earth's precise position in its orbit year over year, you'd find an average yearly discrepancy of 26 seconds.