Did you know that 2024 is a leap year? That means we get to enjoy one more day in February than usual. But why do we need this extra day, and what does it have to do with the seasons and the Sun? Let’s find out!
What Is a Leap Year?
A leap year is a year that has 366 days instead of the usual 365 days. The extra day is added to the end of February, making it 29 days long. This extra day is called a leap day or an intercalary day.
Why Do We Have Leap Years?
We have leap years to keep our calendar in sync with the astronomical seasons. The seasons are determined by the position of the Earth in its orbit around the Sun. It takes the Earth about 365.242189 days, or 365 days, 5 hours, 48 minutes, and 45 seconds, to complete one orbit around the Sun. This is called a tropical year or a solar year.
However, our calendar has only 365 days in a common year (a non-leap year). This means that our calendar year is slightly shorter than the tropical year by about 6 hours. As a result, our calendar gradually drifts away from the seasons by about one day every four years.
If we didn’t add a leap day every four years, our calendar would be out of sync with the seasons by about 25 days after 100 years. This would mean that the months we call February and March would feel like summer in the Northern Hemisphere, and Christmas would be in the middle of summer!
To prevent this from happening, we add a leap day every four years to make up for the lost time and realign our calendar with the seasons.
How Do We Know If It’s a Leap Year?
There is a simple rule to determine if a year is a leap year or not. A year is a leap year if it is divisible by 4, except if it is also divisible by 100, then it is not a leap year, unless it is also divisible by 400, then it is a leap year.
For example, the year 2000 was a leap year because it was divisible by 4, 100, and 400. The year 1900 was not a leap year because it was divisible by 4 and 100, but not by 400. The year 2024 is a leap year because it is divisible by 4, but not by 100 or 400.
You can also use this handy rhyme to remember the leap year rule:
Thirty days hath September,
April, June, and November.
All the rest have thirty-one,
Except for February alone,
Which has twenty-eight days clear,
And twenty-nine in each leap year.
