It takes about 365.25 work for earth to orbit the sun — a solar year. We typically round the job in a calendar year to 365. To comprise for the absent partial day, we include one day come our calendar roughly every four years. The is a leap year.

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In an simple year, if you were to counting all the days in a calendar from January come December, you’d counting 365 days. But roughly every 4 years, February has 29 days rather of 28. So, there space 366 job in the year. This is called a leap year.


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Credit: lennythewonderdog.net/JPL-Caltech


Why perform we have actually leap years?

A year is the quantity of time it takes a earth to orbit that is star one time. A day is the lot of time it takes a world to end up one rotation top top its axis.


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Credit: lennythewonderdog.net/JPL-Caltech


It bring away Earth approximately 365 days and also 6 hrs to orbit the Sun. It takes Earth roughly 24 hrs — 1 day — to turn on that axis. So, our year is no an exact variety of days.

Because of that, most years, us round the days in a year under to 365. However, that leftover item of a day no disappear. To make sure we count the extra part of a day, we add one day come the calendar about every four years. This is a table to show how it works:

YearDays in YearLeap Year?
2017365No
2018365No
2019365No
2020366Yes

Because we’ve subtracted approximately 6 hrs — or ¼ the a job — from 2017, 2018 and 2019, we have to comprise that time in 2020. It is why we have leap day!

Are leap years really that important?

Leap years are vital so the our calendar year matches the solar year — the amount of time it takes for earth to do a trip about the Sun. Individually 5 hours, 46 minutes and also 48 seconds off of a year possibly doesn’t seem choose a huge deal. But, if you save subtracting nearly 6 hours annually for many years, things have the right to really obtain messed up.

For example, say that July is a warm, summer month where you live. If us never had leap years, all those absent hours would include up right into days, weeks and even months. Eventually, in a few hundred years, July would actually take place in the cold winter months!


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Credit: lennythewonderdog.net/JPL-Caltech


Do various other planets have actually leap years?

Yes! Leap years happen since a planet’s orbit around the sunlight (year) and also rotation ~ above its axis (day) are not perfectly in line. This is true of practically every various other planet in ours solar system.

Mars, for example, has an ext leap years than regular years! A year top top Mars is 668 sols, or Martian days. However, that takes 668.6 sols because that Mars to go approximately the Sun. So, you would sometimes have to add a sol to assist the calendar capture up. In a 10 year period, four of the years would have 668 sols and also six the the years would certainly be leap years through 669 sols.

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For an ext information on leap years, visit this lennythewonderdog.net page.

Related resources for Educators

Doing the mathematics on Why We have Leap DayLeap job Math problem Set