Ask A Scientist© Astronomy Archive

   name         johanne kojoian
>>   age          30s
      
>>   Question -   Last night were at a super and were discussing the earth
>and we were aguing about the speed of the earth rotating on it's axis can
>you help us on that one.
>>
>>we all agreed that it take 24 hrs to go around the sun


It takes the Earth about 365.24 days to go around the Sun.  The 24-hr
period is the time it takes the earth to rotate about its own axis.

Actually, the time it takes the Earth to rotate once about its axis is a
little shorter than the 24-hour "solar" day we're accustomed to.  A "solar"
day is defined as the average time from high noon to high noon, that is,
the interval between the times when the Sun is highest in the sky.  Because
the Earth orbits the Sun, by the time it completes one revolution, the
location on the earth closest to the sun has shifted a bit.  The Earth then
needs to rotate a little more to make it line up again.   The time for one
true rotation is the interval between the times that a distant star is
highest in the sky, "fixed star to fixed star."  This interval is known as
a "siderial" day, which is 23 hours, 56 minutes, 4.06 seconds.


                Richard Barrans Jr., Ph.D.
                Chemical Separations Group
                Chemistry Division CHM/200
                Argonne National Laboratory
                9700 South Cass Avenue
                Argonne, IL 60439
                richb@anl.gov

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It takes 1 day (24 hours) for the earth to rotate once on it axis.  It takes
1 year for the earth to go all the way around the sun.

Steve Ross

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Joanne,

While it's true that the Earth makes a complete rotation on its axis in 24
hours, this is different from the time it takes to go around the sun.

The 24-hour rotation is the spinning of the Earth - what causes days and
nights.  It takes the Earth 365.25 days to go around the Sun.  This is
referred to as a revolution, and, combined with the tilt of the Earth on
its axis, is what causes seasons.

Hope this helps.

-Spence
Spencer Pasero