how much time is gained or lost each year, and what is done to account for that time?

Question

wikipedia states that the average year is 365.2425 days. taking leap years into account we measure each year as exactally 365.25 days. wont the .0075 days we cut off eventually add up? By the math I did It averages out to almost 11 minutes a year!

Answer 1

The year that is of interest to us Earthlings, is called the tropical year: that is the period taken by the sun to travel from one tropic to the other and back. It is also the period that best represents the average time between the return of the seasons (as defined astronomically: the passage of the Sun at the point of Vernal Equinox near March 21).

Tropical year = 365.242190 days of 86,400 seconds each.

Our calendar system is presently based on the reform undertaken under Pope Gregory XIII. It is called the Gregorian calendar: one leap year every 4 except on 'century years' not divisible by 400 (e.g., 1900 and 2100 are not leap years).

The average Gregorian year is 365.2425 days.

If you only look at a short period (like one lifetime), it does appear that the average year is 365.25 but that is the old Julian calendar. Over longer periods, use the Gregorian.

The difference is 365.24250 - 365.24219 = 0.00031 day = 26.8 seconds per year. The Gregorian calendar is longer than the 'real' year by 26.8 seconds, which means that it will have lost an entire day in 3,226 years (give or take a few).

Therefore, somewhere in the 53rd century, we should skip a leap year. I do not know if there are formal plans to do that. One could imagine a party on February 28, 5200 to indicate that there will be no February 29 that year.

If we are still here to worry about it...

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This is not the same as the leap second. The leap second is added because the rotation of the Earth is not regular enough.

Right now, the time it takes the Earth to rotate once in relation to the 'average' position of the Sun, is 86,400.0004 seconds. The difference is small enough that we have not had leap seconds for a while.

However, will the occasional shifting of matter within Earth (for example, at the big Tsunami in 2004), our spin rate changes a bit. In the old days, we used to change the definition of a second (we assumed the Earth was regular and our clocks were not).

Then, with more accurate atomic clocks, it became apparent that the problem was not our clocks but the irregularity of Earth's rotation. If we leave the changes uncorrected, we could find ourselves with a Sun that rises at noon -- however, that would take thousands of years.

Therefore, every time the correction to the rotation rate accumulates to a full second, we add or subtract a second.

The problem with the calendar is the number of whole days between one passage at the equinox and the other. The calendar tries to keep the average date of the equinox at March 21 every year.

This problem can only be corrected with whole-day corrections, not by leap seconds.

Answer 2

Leap seconds
Leap seconds are added to keep the clocks synchronized with the Earth's rotation.
Basic details
The second is the base unit for modern time keeping. The second was previously defined based on the Earth's rotation, but because modern atomic clocks are more accurate than the Earth's rotation the definition was changed in 1967. A second is currently defined as being the duration of 9,192,631,770 periods/oscillations of radiation from a Cesium-133 atom at the ground state (near 0 Kelvin - coldest possible).

The Earth is rotating slower and slower over time, while the atomic clocks are not slowing down. On one average day the difference is around 0.002 seconds, which means around 1 second in 500 days. In order to synchronize the atomic clocks with the Earth's observed rotation, the atomic clocks are occasionally instructed to add an extra second – the leap second. Leap seconds are inserted so that the difference between the UTC (Coordinated Universal Time) and UT1 (mean solar time - observed Earth rotation) is kept below 0.9 seconds.

The leap second is added in the end of June or December. It is also possible to have a negative leap second, where one second is removed, in a case where the Earth is rotating faster, but such a negative second has never been used, and is rather unlikely to be used in the future

Answer 3

In addition to the two previous answers, there is such a thing as leap seconds. Leap seconds attempt to synchronize the small changes in earth's rotation caused by tides and internal magma flow with an atomic clock. The US Naval Observatory, the US timekeeper, calculates when leap seconds should be inserted.

There have been 23 leap seconds since this was started in 1972, the last insertion of a leap second was 2005-12-31 at a time of 23:59:60

Answer 4

That was the problem with the Julian calendar, in which the year was indeed 365.25 days. But by the sixteenth century, all those eleven minutes had added up and the calendar was off by about eleven days. Pope Gregory's astronomers recommmended a change such that century years would not be leap years unless the year was a multiple of 400. This was adopted in Europe at the time, and by England in about 1751, and remains in effect today. So 2000 was a leap year, but 2100 will not be. The remaining error is about one day in 3300 years.

Answer 5

The Gregorian calendar, the current standard calendar in most of the world, adds a 29th day to February in all years evenly divisible by four, 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.

Answer 6

That is why a century leap year can only occury if the year is divisive by 400.

For example, 1700 would not be a leap year since 1800/400 is 4.5 even through it divides by 4.
2200 will be the next skipped year.

The next time we'll need to worry about the extra day catching up with is will be around 4882 and I intend to be long dead by then.

Hope that answers your question.

Answer 7

Actualy, earth is slowing down. Tides cause friction. We gain about .0005 seconds a CENTUARY in earth's solar year. At some point, we will have to either legnthen an hour or add time to a day because our days get longer.

Amazing. Soon(in about a million years, littarly) Humans will have to leave earth to go to a planet that is not dying