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Earth's orbit and relative speed/time

  1. Oct 17, 2011 #1
    Hi,

    I am curious whether that when the Earth is in its closest position to the Sun, the Suns gravitational pull has a direct effect on the Earths orbital speed. Since the speed of an object has an effect on time. Would the increase in speed affect time in general. Of course the time is relative to us.

    I apologise I am struggling to word this.
     
  2. jcsd
  3. Oct 17, 2011 #2

    Bill_K

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    Relativistic effects generally require relativistic velocities. The average velocity of the Earth around the sun is 29.7 km.sec, which is 10-4 of the speed of light. So the time dilation of Earth time as measured by an observer stationary with respect to the sun would be about a part in 10-8. The velocity varies from 29.3 at aphelion to 30.3 at perihelion, about one percent.

    On the other hand, the velocity of the sun around the center of the Milky Way is one order of magnitude greater, 220 km/sec. And the velocity of the Local Group of galaxies with respect to the cosmic microwave background is greater still, 600 km/sec.

    Remember that time dilation is relative, not absolute, it's in the eye of the observer. You could still argue that being at rest in the CMB is more fundamental than being at rest on the Earth, and moreover the Earth is accelerating.
     
  4. Oct 17, 2011 #3

    D H

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    There are two effects, a special relativistic effect due to the Earth moving slightly faster at perihelion, plus a general relativistic effect due to perihelion being slightly deeper in the Sun's gravity well. The combined effect is very small, on the order of microseconds.

    See http://adsabs.harvard.edu/full/1998A&A...336..381S.
     
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