The History of Leap Year | By Abigail Poh Lin Xian
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| Illustrated by: Emelyne (@realm_of_makia) and Suchethaa (@suchethaasgp) |
Can you name something that comes around every four years? Most people would probably say the Olympics, the US presidential elections, and of course, leap years. Everybody knows about leap years. Every four years, they give us one extra day in February to while away. However, many of us probably haven't stopped to think about why they even exist in the first place.
Leap years are calculated by dividing the year by four. If the number is divisible, then you get a leap year. If the year is at the end of a full century, the leap year status is determined by whether it is divisible by 400. While the calculations are pretty straightforward, the history of leap year, time counting and their incorporation into the calendar is rather complex and fascinating. To understand leap years, we need to look at calendars and time.
These days, we take calendars for granted: available in physical and digital formats, our time is chopped up into neat 24-hour segments that make up our days, weeks, months and years. Counting time is much more important than you think—time controls our entire lives and the systems we use ensure the world runs smoothly. Governments, economies, industries and more have always relied on good timekeeping. As such, humans pursued it with tools, from rudimentary sundials to atomic clocks.
The ancient Egyptians were one of the first to figure out a timekeeping system. By using sundials, shadow clocks (an improved type of sundial) and plumb lines called Merkhets, they observed the sun's and stars' movements to divide the day into 12 segments between dawn and dusk, laying the foundation for calendar days.
The 7-day week came from the Jews and was later officially adopted by Emperor Constantine in 4 AD. The Babylonians and Persians used natural cycles based on the moon and sun to form early calendars. Later on, the more refined Julian calendar was formed under Julius Caesar. Eventually, the Romans became one of the earliest civilizations to incorporate the leap year into their calendar in 45 BCE.
So, what is the exact purpose of leap year? On the surface, it simply adds a day to the calendar, but it has a vital role in preventing time drift, which could lead to a mismatch between dates on a calendar and the Solar System. This discrepancy arises as the Earth does not actually orbit around the sun for exactly 365 days (even though that would be convenient for us, wouldn't it?) Instead, it takes about 365 ¼ days to complete a full rotation around the sun.
These quarters add up to nearly a full day every four years, thus constituting an additional day. Over time, seasons would drift away from calendar dates if we didn’t take this additional bit of time into account as they moved by ¼ of a day. While initially unnoticeable, it would eventually escalate to the point where seasons would start months away from their original place. The whole point of a calendar, which is to keep time consistent, reliable and predictable, would be forfeited. Considering that time impacts everything from farming to the economy and space research, it is safe to say that leap year is instrumental to the very concept of timekeeping itself.
In this day and age, the Gregorian calendar is the most widely used in the world. It provides a standard that allows governments and businesses worldwide to function and collaborate efficiently. Throughout history, though, various ethnic groups worldwide have developed their own ways of timekeeping. Whether for trade, religious reasons or recordkeeping, calendars have played a big role in culture for a long time. For example, the Mayans used two cyclical calendars that ran alongside one another and determined whether activities such as trade or war should be conducted based on their interpretations. As mentioned earlier, leap year was included as early as 45 BCE in the Julian Calendar. These days, it is added to February for practicality’s sake since it is the shortest month of the year.
Interestingly, other calendars have very different methods of implementing leap years. The Bengali calendar includes its leap day in the eleventh month, known as Falgun. Meanwhile, the Chinese calendar adds an entire month into a leap year about once every three years, thus causing that year to have 13 months instead.
Leap year represents a rare intersection of science, history and culture for humanity. Thanks to its existence, we can sync calendars with our planet's movement, ensuring everything from food production to religious celebrations and scientific research can run smoothly. Perhaps the most important part is simply the fact that we get an additional 24 hours to enjoy life. Now that you’ve been given an extra day, what will you do with it? As they say, there’s no time like the present.
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