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Knowledge_Seeker
2006-Aug-29, 02:58 AM
First of all, how long exactly is a day here on earth?

My man question was ive heard that the earth is slowing down, i know this is true, but by how much?

I believe it is by a billionth of a second a day and is continuing to slow down like a top. And if the earth is indeed like a top, wat happens when it stops?

01101001
2006-Aug-29, 03:10 AM
What is your definition of a day?

Wikipedia: Day (http://en.wikipedia.org/wiki/Day)

International System of Units (SI) -- A day is defined as 86,400 seconds.

Astronomy -- For a given planet, there are two types of day defined in astronomy:
1 apparent sidereal day = a single rotation of a planet with respect to the distant stars (for Earth it is 23.934 solar hours or 24 sidereal hours)
1 solar day = a single rotation of a planet with respect to Sun.
Leap seconds are added to some days, changing the average length of a day, to keep days aligned with the apparent movement of the sun. See International Earth Rotation and Reference Systems Service (http://www.iers.org/)

cjl
2006-Aug-29, 04:31 AM
First, the earth will never stop. It will become tidally locked with the moon someday, and the day will be somewhat longer than a current month. Eventually, it would become tidally locked with the sun, but that won't happen before the sun turns into a red giant and essentially destroys the earth anyways.

hhEb09'1
2006-Aug-29, 04:33 AM
I believe it is by a billionth of a second a day and is continuing to slow down like a top. And if the earth is indeed like a top, wat happens when it stops?On average, over the past few thousand years, it's been about 2 msec per day per century. That's, what, about half of a billionth of a second per day, per day, so you were close there. The length of our day was set to a standard from about a hundred years ago, so it is now about 2 msec shorter--which means that about every 500 days (500 x 2 msec = 1 sec), we were adding a leap second.

But it's actually sped up some over the past five years, so it's not constant. The main reason that it is slowing is the moon's tidal effect, which will stop when the moon's orbital period matches the earth's rotation. That is so far into the future, that the solar system itself probably won't be around.