This question came up in my summer Bible study on The Story: Did Joshua cause leap years by praying for the sun to stop?
Christians naturally want to pass along any information that might influence agnostic friends to trust the Bible. That’s great when the details are solid, but sometimes inaccurate claims bounce around, and when we latch onto one of those, skeptics mock and we get results opposite of what we want. Not fun.
One such claim currently traversing the Internet is that Joshua’s prayer for the sun to stand still during a battle (Joshua 10:12) combined with Isaiah’s prayer for a shadow to retreat ten steps (2 Kings 20:11) resulted in a lost day that has to be made up for with leap years.
So did Joshua cause leap years?
We don’t periodically add a day to February because of an astronomical anomaly three millennia ago—that would be like saying a train was late once in 1842 and Amtrak has to adjust all its train schedules every few years to compensate.
Why We have Leap Years
We have leap years so our seasons will start on about the same calendar date each calendar year. If we never observed leap years, we’d eventually celebrate the Fourth of July in the middle of winter.
Here’s the technical explanation. Our seasons begin when the earth is at specific points in its orbit around the sun. The earth takes 365 days 5 hours 48 minutes 46 seconds to orbit the sun—a period of time called a tropical year. A calendar year tracks only full days, so after four calendar years, that nearly six-hour lag behind the tropical year accumulates to almost twenty-four hours. We add a day to the calendar year to synchronize it with the tropical year.
This allows us to keep the solstices (when the sun is farthest from the equator, causing the shortest and longest days of the year) always near December 21 and June 21, and the equinoxes (when the sun crosses the equator, causing day and night to be nearly the same length) always near March 20 and September 22. Summer and winter start on the solstices; spring and fall start on the equinoxes.
Even if you don’t live in the parts of Alaska where the sun doesn’t rise on December 21 and it doesn’t set on June 21, you probably find planning easier knowing which months are hottest and which are coldest. (Unless you live near the equator where day lengths don’t vary much—Hawaii’s longest day is 13.5 and shortest 11.)
The extra calendar day is added to the end of February and is called a leap day. A year in which we add a leap day is called a leap year. We have leap years about every four years. But because a leap day overcompensates by 11 minutes and 14 seconds, we skip adding a leap day three times over every four centuries.
For those who like such things, here’s how to figure out which years are leap years. Years evenly divisible by four are leap years except for years also evenly divisible by 100 but not by 400. Thus 2012 and 2000 were leap years, but not 1900 (2012 is evenly divisible by 4, but not 100; 2000 is evenly divisible by 4, 100, and 400; 1900 is evenly divisible by 4 and 100, but not 400).
Test everything. Hold on to the good. ~1 Thessalonians 5:21