# Leap Years

## Leap Year

- A normal year has 365 days.

- A
**Leap Year**has 366 days (the extra day is the 29th of February).

## How to know if a year will be a Leap Year:

Leap Years are any year that can be evenly divided by 4 (such as 2012, 2016, etc) |
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except if it can can be evenly divided by 100, then it isn't (such as 2100, 2200, etc) |
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it can be except ifevenly divided by 400, then it is (such as 2000, 2400) |

## Why?

Because the Earth rotates about **365.242375** times a year ...

... but a normal year is **365** days, ...

... so something has to be done to "catch up" the extra **0.242375** days a year.

- So every 4th year we add an extra day (the 29th of February), which makes
**365.25**days a year. This is fairly close, but is wrong by about 1 day every 100 years. - So every 100 years we
**don't**have a leap year, and that results in**365.24**days per year (1 day less in 100 year = -0.01 days per year). Closer, but still not accurate enough! - So another rule says that every 400 years
**is**a leap year again. This gets us**365.2425**days per year (1 day regained every 400 years = 0.0025 days per year), which is close enough to 365.242375 not to matter much.

## So, which Are and which Aren't?

So 1600, 2000 and 2400 **are ** leap years but 1700, 1800, 1900, 2100, 2200 and 2300 **are not**.

Apart from that, **every year divisible by 4** (2012, 2016, 2020, etc.) is a leap year.

How far away each year is from the average |

As you can see, this keeps us pretty close, and any other adjustments can be done way in the future (when the Earth may be rotating a little slower, anyway!)