How would you define a year? To many people, it’s the time from birthday to birthday, or it might be the days from January 1 to December 31. This is known as a calendar year. A year might also be defined as the time it takes for the earth to orbit the sun. This is called a solar year. The problem is that the earth takes about 365.25 days to go around the sun in relationship to the stars. Over time, this means that every four years, the earth is out of sync with the calendar by one day. Pioneers in science realized that this would be a problem.

This may not seem like a big deal in one person’s lifetime, but after 100 years, the calendar and solar years would be out of sync by 25 days. The calendar might say March 20, the first day of spring, but the solar system would be well into the growing season. In a few more centuries, people might be celebrating Christmas during the summer. Because the world relies on the calendar year, instead of the solar year, it’s imperative that the two be in sync.

Astronomers Noticed Problems with the Calendar and the Seasons

Julius Caesar and a group of scientists and astronomers in the first century studied and researched this phenomena, but they didn’t really have a scientific plan to offset the problem. His calendar system, known as the Julian calendar, sometimes added an extra day to February. In the 1500s, the calendar and the seasons were still off by about 11 days. Pope Gregory XII and his astronomers continued to observe and study this problem with time. Eleven days were added. In 1582, everyone went to bed on March 11 and woke up on March 22.

Using mathematics, technology of the time, and science, the Pope’s astronomers came up with the current calendar system, the Gregorian calendar. This is where the science of leap year started. One additional day would be added to the calendar every four years. In the Gregorian calendar, century years would only be leap years if they were divisible by 400. It was a small change, but necessary to keep the seasons and calendar in sync. Because the solar calendar isn’t exactly an extra one-quarter day, in about 3,000 years, scientists will need to further adjust the calendar.

Leap Year Traditions

Legend has it that in the 5th century, St. Patrick of Ireland gave permission for women to propose to men on February 29. Another tradition states that if the man refused the proposal, he would have to pay a fine to the lady, like maybe buy her a skirt or new pair of gloves. In Greece, it’s considered bad luck to begin an engagement or get married during a leap year.

Each state has different laws about how birthdays on February 29 are handled when it comes to getting your driver’s license. In Michigan, leap year babies have to wait until March 1 to go to the DMV, but in some places the date is February 28. This law doesn’t affect too many people in the United States, only about 187,000. A baby only has about a 1 in 1,500 chance of being born on February 29.

Take time this year to make February 29 a day of science and knowledge. Study astronomy to understand the early scientists who gave us leap year. Much of today’s GPS technology and advancements in aerospace is thanks to the understanding and science of the stars. Scientists developed theories about the nature of the stars by studying their position. Look to the sky and see the beauty, but don’t forget to see the physics and science of the observation of the stars.