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The science behind the leap: Leap year 2020

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February 28, 2020
By Emily Sandberg

You’ve probably heard that 2020 is a leap year, but are you familiar why? No, it’s not because February 28 needed a friend. It’s because of astronomy! 

Every four years, an extra day is added to the month of February. February 29th, also known as Leap Day, was implemented to keep the calendar in line with Earth’s orbit around the sun. Our calendar contains 365 days, but the Earth actually takes around 365.242 days to orbit the sun. To make up for this small difference, we add an extra day to the calendar every four years. It’s a great way to enjoy an extra day of doing something you love, such as seeing a show at your favorite planetarium!

Person leap
Credit: CommPartners

Adding an extra day wasn’t just a random decision—Rome wasn’t built in a day, and neither was the modern calendar. In 46 B.C., the Greek astronomer Sosigenes used Egyptian calculations to create the “Julian Calendar” (named after Roman general Julius Caesar), which included 365 days, and 366 every four years. 

However, the Julian calendar had one major problem: a real solar year is .242 days longer than the calendar year, not a perfect .25. So, this calendar created a difference of about 11 minutes each year. While this may not seem like a major issue, those eleven minutes add up in the grand scheme of things. Every 128 years, the Julian calendar would stray from the solar year by one day.

How did we solve this complication? Well, we can thank Pope Gregory XIII. The “Gregorian Calendar”, the calendar we use today, used an adjusted mathematics formula to fix the discrepancy. It instituted modern leap days, which occur every four years except in years divisible by 100 and not 400 (for example, the year 1900). Although this calendar isn’t perfect, it’s good enough to last us 10,000 more years according to modern astronomers. 

As for the name itself, we use the word “leap” to describe these years because they do just that. In a leap year, the dates jump over one day of the week. For example, if July 4 is on a Wednesday one year, it will be on a Thursday the next. However, if that next year is a leap year, July 4 would be on a Friday. The calendar “leaps” forward two days, instead of the usual one!

2020 is an important year, but not just because it’s a leap year— it’s also a U.S. presidential election year and a Summer Olympics year! Remember Pope Gregory’s rules for determining leap years? They not only ensured that the calendar would closely represent the Earth’s cycle around the sun, but also that leap years would fall on U.S. election and Summer Olympic years.

Unsure of how to spend your extra day this year? We’ve got an idea! What better way to celebrate a day that only comes every four years than by spending it under the stars at Morehead. For the first time since 1992, Leap Day is on a Saturday this year and we are open for business. Come visit!