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Leap Year Lesson for Kids: Definition & Facts

Instructor: Suzanne Rose

Suzanne has taught all levels PK-graduate school and has a PhD in Instructional Systems Design. She currently teachers literacy courses to preservice and inservice teachers.

Did you know that not all years have the same number of days? In this lesson, you'll find out about what a leap year is, how many days it has, and why those extra days are needed.

How Many Days Are in February?

Are you ever really busy and just wish you had more time? Well about every four years, you get your wish! Instead of the 365 days that we usually have in a year, a leap year has 366 days!

Leap Day is February 29
day

This extra day is added to the month of February, which normally has 28 days. So, in a leap year, February has 29 days. Let's look at why we need this extra day and how it was added to our calendar.

Tropical Years, Common Years, and Leap Years

A year is usually defined as the amount of time it takes a planet to complete one orbit around the sun. For Earth, this takes 365 days, 5 hours, 48 minutes, and 45 seconds, or about 365 ¼ days. This is called a tropical year or a solar year.

A common year, which is what we see on a calendar, has 365 days. Do you notice a problem? Even though it takes the Earth about 365 ¼ days to go around the sun, our calendar only has 365 days in a common year. This means that every so often, we need to add an extra day to our calendar to make it match up with the tropical year again.

The Julian Calendar

Julius Caesar, a soldier and politician who lived in Rome about 2000 years ago, came up with the idea of correcting the calendar. His idea was to add one day to the calendar every four years if the year was evenly divisible by four. So, for example, the year 1200 is evenly divisible by four, so it would be a leap year, while the year 1350, which isn't evenly divisible by four, wouldn't be a leap year.

Julius Caesar
julius

This was called the Julian calendar, and it was used for about 1500 years. Caesar had a clever idea, but it ended up adding too many extra days to the calendar.

The Gregorian Calendar

An Italian scientist, Luigi Lilio, realized that there was a problem with the Julian calendar and came up with a new way to figure out when to add the extra day to the calendar so that the common year and the tropical year would stay closer together.

His calendar was called the Gregorian calendar, named after Pope Gregory XIII. This revised calendar calculated leap years differently than the Julian calendar. To be a leap year in the Gregorian calendar, a year:

  • Must be evenly divisible by four
  • Must not be evenly divisible by 100

There's one exception to the second rule: If the year IS evenly divisible by 100, it can still be a leap year if it's also evenly divisible by 400.

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