why do we have leap years?

Question

isnt it so certain months have the same seaons year round?

Answer 1

A leap year (or intercalary year) is a year containing an extra day (or, in case of lunisolar calendars, an extra month) in order to keep the calendar year synchronised with the astronomical or seasonal year. For example, February would have 29 days on a leap year instead of the usual 28. Seasons and astronomical events do not repeat at an exact number of days, so a calendar which had the same number of days in each year would over time drift with respect to the event it was supposed to track. By occasionally inserting (or intercalating) an additional day or month into the year, the drift can be corrected. A year which is not a leap year is called a common year. In fact, the Earth takes slightly under 365 1/4 days to revolve around the Sun.

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Answer 2

Leap years are needed so that the calendar is in alignment with the earth's motion around the sun. The vernal equinox is that time when the sun is directly above the Earth's equator, apparently moving from the southern to the northern hemisphere.

The mean time between two successive vernal equinoxes is called a tropical year, and it is about 365.2422 days long.

Using a calendar with 365 days would result in an error of 0.2422 days or almost 6 hours per year. After 100 years, this calendar would be more than 24 days ahead of the seasons (tropical year), which is not a desirable situation. It is desirable to align the calendar with the seasons, and make the difference as small as possible.

By adding leap years approximately every 4th year, this difference between the calendar and the seasons can be reduced significantly, and the calendar will follow the seasons much more closely than without leap years.

Answer 3

The leap year is a contrivance so that the calendar year (usually 365 days) doesn't get too far away from the solar (astronomical) year. The time it takes the earth to go exactly once around the sun – is not precisely 365 days. The ancients estimated it as 365¼ days. That wasn't bad as calculations go; it's actually 365 days, 5 hours, 48 minutes, and 46 seconds.

Answer 4

Basically yes, though particular months can't really have "the same seasons year round". I assume you meant to say that over long periods, say several lifetimes or centuries, a given month will still occur in the same season. If we didn't care then why bother? This kind of illustrates the point because the Gregorian calendar reform was primarily a religious issue over setting a day to celebrate Easter. You will note that in Islam Ramadan happens when it happens and it doesn't matter (at least it seems so to me) what season of the year this turns out to be. Then again the Hebrew calendar inserts an extra month now and then which does have the effect of keeping their festivals generally in line with seasons.

Answer 5

Because the earth takes just slightly more than a "year" to go around the sun. 365 1/4 days actually

http://en.wikipedia.org/wiki/Leap_year

Answer 6

because a year isnt really 365 days. its 365 and 1/4 days. so we add an extra day every 4 years to catch up.

Answer 7

It's needed because there are 365.25 days in a year. We have a leap year every four years to make up for this .25 every year.