WeatherWhys Blog

Leap Day - Its earlier than you think

Leap Day - Its earlier than you think

Here comes another presidential election and thus a leap year. Every 4 years February grows by one day. But why?

February has always been just a little different from any other month. It is the only month that begins with an “F”, includes Valentine’s Day, Ground Hog Day, and the birthdays of both Abraham Lincoln and George Washington. But it is also a conspicuously short month- only 28 days. As if that wasn’t interesting enough in every year divisible by 4, one additional day is added to the month.

The earth revolves around the sun in about 365 ¼ days. That is, it goes from one specific spot in its orbit to that same spot. It is our solar reckoning of time. Why is that important? It matters since the earth is tilting about 23 ½ degrees on its axis, and so the North Pole points away from the sun at a certain time each year. That time is called the Winter Solstice. Additionally, there is a moment in which the North Pole point most directly toward the sun. This instant in time is known as the Summer Solstice. These events correspond to dates. But this inconvenient imprecision of the orbital time, and the number of days to accomplish a complete circuit around the sun, gets a little messy when attempting to reconcile our calendar.

So every 4 years the remaining ¼ day adds up to one full day. We add it to February so that the calendar matches actual solar time. If the Leap Day was NOT added a discongruency would accumulate in our calendar such that at some point in the future it would be cold and dark at the Winter Solstice- but the calendar would say “May” or “June”. Calendar time is too fast. So to prevent that situation from happening, at the end of February, we stop time for one day. When it should have become March 1st, we let an additional 24 hour pass essentially letting our orbit around the sun catch up with the calendar. Once that extra day has ticked off, then we can let the clock and calendar pick up where it left off again.

Why February? This is due to the fact that March 25th was New Year’s Day for millennia, coming at the Vernal Equinox or first day of spring. But America and all British citizens changed their calendar to the Gregorian style 260 years ago. The Gregorian Calendar starts its year on January 1st. The previous Julian Calendar started in March, when spring and everything new began. Hence, February was the last month of the year and it was decided that all adjustments to the year would be tacked on there.

And now you know the rest of the story.