Welcome to the leap year day!

Today is 29 February 2020, also known as the leap day or leap year day. Those born on leap year days are called leaplings.

Excuse me, are you a leapling?

What is a leap year? Why is it in February? And how did our calendar come about? Here are some fun facts and fun math around calendars.

February 29 is a date added to most years that are divisible by 4, such as 2016 and 2020 and 2024. Our modern calendar is based on the Gregorian calendar, named after Pope Gregory XIII who introduced it in 1582 (that’s over 430 years ago!). The extra day is added because the Earth revolving around the Sun takes approximately six hours longer than 365 whole days. If not added in, the seasons will end up being later and later over the years.

A Brief History of Calendar Systems and Missing Days

Before the Gregorian calendar, we had the Julian calendar, named after Roman emperor Julius Caesar who introduced it in 46 BC (wow, that is over 2060 years ago). Julius Caesar was the one who made changes to the Roman calendar including adding the leap year day in. In older times, most people used a lunar system by observing the moon. The problem with the lunar system is that a lunar month is about 29.5 days, which makes it 29.5 x 12 = 354 days. Some ancient civilizations (like the Egyptians) who studied the solar movement added 11 days to the calendar. It still resulted in fewer days, hence Julius Caesar added an extra day to the Roman calendar on the shortest month of the year, February.

(Here’s a simple Math. If Earth takes 6 hours longer than 365 x 24 hours each year, how many years will it be before it becomes a whole day longer? Clue: That would be 24 divided by 6. )

Actually, it is a little more complicated than adding a day every 4 years because it is not exactly 6 hours but a bit shorter, so we devised other ways to compensate this by having years that are divisible by 100, but not by 400, which will not be a year containing a leap day. Pope Gregory XIII modified the Julian calendar because every 400 years, there were 3 days too many added. To make life even more complicated, even this does not fully adjust our timing to the Earth’s revolving around the sun so the concept of leap second was introduced, but that is another complicated story for another time (if you have a second to spare, pun intended).

For those who like Math and computational thinking a lot, here’s how you can decide what is a leap year:

if (year is not divisible by 4) then (it is a common year)
else if (year is not divisible by 100) then (it is a leap year)
else if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)

* Common year means not a leap year.

Back in the old days, the world was not so connected and rivalry between countries were strong. Civilizations follow their own calendar systems. When Pope Gregory XIII came up with the revised calendar, some countries did not like to follow a system devised by the Catholic Church until much later. For example, Russia did not convert to the Gregorian calendar until after the Russian Revolution in 1917. The funny thing was, in 1908, the Russian Olympics team arrived 12 days late to the London Olympics because of this! Ouch. Hope they got to do some good sightseeing.

Months of the Year

As an additional fun fact, do you know how the months were named? The months followed the naming by the Romans. In fact, March used to be the first month of the year. January and February were not given names in ancient times because the calendar was first devised to help in farming cycles and there were no farming activities during these two months.

March was named after Mars, the Roman god of war. In the first two months of the year, all activities were stopped. Any military campaign would resume only in March, the official first month of the year.

Following this, we therefore have names like September (Septem is seven), October (Octo is eight), November (Novem is nine) and December (Decem is ten). Originally, July and August were named after Roman numerals but were changed by the Romans to honour their great emperors Julius Caesar (July) and Augustus Caesar (August).

(Simple Math – if March is the first month of the year, which month of the year is December?)

Okay, enough of fun facts for a leap year day. Now you can tell your friends, “Now I know my Leap Year Facts, won’t you come and play with me?” (sung to the tune of Now I know my ABC). Have A great leap year day – Find all leaplings and give them a hug!

Sources:

  1. https://en.wikipedia.org/wiki/Gregorian_calendar
  2. https://en.wikipedia.org/wiki/Leap_year
  3. https://gizmodo.com/the-evolution-of-the-modern-day-calendar-1283885844
  4. https://www.almanac.com/content/how-did-months-get-their-names

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