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Solar day and the amount of Earth's rotation

  1. Aug 14, 2015 #1
    Hi. I am confused about something and it is making me feel rather stupid.

    First of all i will explain what i know. I know a solar day is 24hrs long and it is defined by the position of the sun. I also know a sidereal day is 23h 56m and is defined by the postition of the stars (basically).

    The problem i have is with the solar day. As the earth rotates it also orbits the sun, and because of that orbit the earth has to rotate a little further each day. If it didnt then the sun would be in a different place.

    I can see in a sidereal day the earth roates 360 deg, however a solar day must be more then 360 degrees surely?

    Sorry for such an infantile question but is it just simply that a the earth rotates more then 360 in a solar day?
  2. jcsd
  3. Aug 14, 2015 #2


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    This is similar to how hands of a clock move. Imagine both hands of the clock start at 12 o'clock.
    Think of how far the minute hand moves in an hour (back to the number 12 on the clock). This is analogous to the sidereal day, as the numbers are static, just like the background stars.
    Now think how far it has to move to catch up with the hour hand. This is analogous to the solar day, where the hour hand represents the sun moving across the sky w/r to the fixed stars, due to Earth's orbit.

    Every full 12 hours, the hands meet only 11 times. Similarly, every year has exactly one less solar day than sidereal days (ignoring other factors, like precession of equinoxes).
  4. Aug 14, 2015 #3
    Yes thought so , just thought i would check. Google says the earth rotates 360 degrees in a solar day and that is what was annoying me. thanks
  5. Aug 14, 2015 #4


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    Just to confirm. The Earth rotates on its axis by approximately (24*60*60)/(23*60*60+56*60) * 360 = 361.0 degrees in a solar day.
  6. Aug 14, 2015 #5

    D H

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    Rotates with respect to what?

    With respect to inertial space, yes, the Earth rotates by about 361 degrees in a mean solar day (86400 seconds). But with respect to the Sun, the Earth rotates by about 360 degrees in a mean solar day.
  7. Aug 15, 2015 #6


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