Where does the extra day come from on a leap year?

Question

I know that there are 365 days in a year but how comes there is and extra day every 4 years and why is it necessary?

Answer 1

The leap year was made so that the calendar year (usually 365 days) doesn't get too far away from the solar (astronomical) year.
The astronomical year is actually 365 days, 5 hours, 48 minutes, and 46 seconds.

Every four years, the calendar would lose a full day against the seasonal year. Christmas would start to come a little earlier each year. After about 20 years it would come before the winter solstice; after 200 years or so, Christmas would come in the autumn .

To prevent this, they make it so that every four years, we add one extra day. This balances it out.

Answer 2

A year is not exactly 365 days, but a bit more, close to 365.25 days (not exactly that, either).

So when we use a 365 day year, after a year we're 1/4th of a day ahead of where the earth really is on its orbit. After 2 years we're 1/2 day ahead. after 3 years, we're 3/4ths of a day ahead.

If we never adjusted anything, after 100 years we'd be 25 days ahead, and pretty soon everything would be wrong (seasons, etc.).

So every 4 years, we add a day, which amounts to the same as adding 1/4th of a day each year, but is more simple to do.


And then it gets a bit more complicated. Adding 1 day every 4 years, which gives a 365.25 days year, is actually a bit too much. So every 100 years, we should add the extra day, but we do NOT. Which gives us a 365.24 days year, which is closer to the real year. And every 400 years we add the day anyway, which takes us to to 365.2425.

Not that simple, I know. Guess "they" should have started off with, say, a 100 day year, or some other round number, and from that deducted the hour, not the other way around. Too late to change now, I guess.

Answer 3

There's actually 365 1/4 days each year - the leap year comes so that we don't lose the seasons which would happen eventually if we didn't have the extra day.

Answer 4

It actually takes 365 and 1/4 days for the earth to orbit the sun. However, that would make everything WAY too complicated so we save up the quarters and have a whole extra day once every four years!

Answer 5

The actual calander is based upon the fact that it takes the Earth 365 1/4 days to make a full orbit around the world, leap year or rather the 29th February makes up for this fact.

Answer 6

the year is not 365 days it is 365 day plus just under .25 of a day to every year we lose a quarter of a day so we put one in every leap year except it is not exactly a quarter so on some leap years we don't do it. I think it is at the end of a century

Answer 7

The problem is that a years is not actually 365 days. A year is measured by the time it takes for the earth to get around the sun. That time is actually closer to 365.25 days. This is why every four years we add 1 day to the year. This helps compensate for the rounding that we do. And as it turns out, even that isn't perfect. As a result we skip leap year every 100 years, unless that is divisible by 400 years. The rules go on and on.

Answer 8

Why are leap years needed?
-Leap years are needed so that the calendar is in alignment with the earth's motion around the sun.

The Gregorian calendar, the current standard calendar in most of the world, adds a 29th day to February in all years evenly divisible by 4, except for centennial years (those ending in -00), which receive the extra day only if they are evenly divisible by 400. Thus 1600, 2000 and 2400 are leap years but 1700, 1800, 1900 and 2100 are not.

The reasoning behind this rule is as follows:

The Gregorian calendar is designed to keep the vernal equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the Moon that falls on or after 21 March) remains correct with respect to the vernal equinox.
The vernal equinox year is currently about 365.242375 days long.
The Gregorian leap year rule gives an average year length of 365.2425 days.
This difference of a little over 0.0001 days means that in around 8,000 years, the calendar will be about one day behind where it should be. But in 8,000 years' time the length of the vernal equinox year will have changed by an amount which can't be accurately predicted (see below). So the Gregorian leap year rule does a good enough job.

A leap year (or intercalary year) is a year containing an extra day, week or month in order to keep the calendar year synchronised with the astronomical or seasonal year. For example, February would have 29 days instead of just 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.

February 29, 2008
Year 2008 is the next leap year, with 29 days in February. February 2008 has five Fridays - it starts and ends on a Friday. Between 1904 and 2096, leap years with same day of week for each date repeat every 28 years which means that the last time February had 5 Fridays was in 1980 and next time will be in 2036.
What is a leap year?
A leap year is a year with one extra day inserted into February, the leap year is 366 days with 29 days in February as opposed to the normal 28 days. (There are a few past exceptions to this)
Which years are leap years?
In the Gregorian calendar, which is the calendar used by most modern countries, the following rules decides which years are leap years:

Every year divisible by 4 is a leap year.
But every year divisible by 100 is NOT a leap year
Unless the year is also divisible by 400, then it is still a leap year.

Answer 9

If memory serves from my GCSE science days, every year has 365 and a quarter days a year. Hence every 4 years, an extra day to ensure our calendar remains on track.

Answer 10

because a year is actually 365 and a quarter days so every four years you get an extra day.