export_ofoct.com

[00:00.12] 2020 is a leap year, and as we all know leap years happen every four years, right? Wrong.

[00:06.23] That extra day in February is designed to keep the Earth in sync with the astrological or seasonal year.

[00:14.73] But, what you might not realise is that the maths isn’t that simple and occasionally we have to wait eight years.

[00:22.70] The method behind calculating when leap years occur might be a bit more complicated than you think.

[00:29.34] Way back in 1582 the calendar we now use was first implemented. The Gregorian calendar was named after the pope at the time, Gregory X1V.

[00:41.83] The people who created it realised it wasn’t perfect to just add an extra day every four years.

[00:49.27] Here’s where the maths comes in.

[00:52.45] A day, of course, is measured by the amount of time it takes for the Earth to complete one full rotation on its axis.

[00:59.09] A year is the number of days it takes the Earth to orbit the Sun, which most people assume is 365.

[01:07.59] However, the Earth actually takes just under 365 and a quarter days to complete one full revolution around the Sun.

[01:19.28] So, every four years we get an extra day, which falls on the 29th February.

[01:25.92] However, as mentioned earlier, it is in fact just under a quarter of a day.

[01:32.56] So, by rounding it up, we put the calendar out of sync again – which means that after a while we have too many days.

[01:43.45] That imbalance has to be readdressed, otherwise after 400 years you’d end up with three extra days.

[01:54.34] So back in 1582, they realised that every turn of a century should skip their extra day to subtract those three extra days.

[02:07.62] This is why the years 1700, 1800, and 1900 weren’t leap years.

[02:15.33] But wait, there’s more. The year 2000, the millennium, was a leap year.

[02:21.17] That’s because over a period of four hundred years we only need to remove three days.

[02:27.28] So, every 400 years the turn of the century is a leap year.

[02:32.86] This means the next time you hear someone saying ‘leap years happen every four years’ you can tell them why they’re wrong.