Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The Sun

  1. Nov 19, 2003 #1
    As light travels at X km/h (pretty fast), and Earth is 155,000,000km away from the Sun, How much would the Earth have rotated from the start of the light ray from the sun to the second it hits Earth?
    Another way of explaining: Looking from Earth, how many degrees would the Sun have moved in the time the light ray left the Sun and reached Earth?
    Or does it point to where the sun is actually located, not it's delayed position?
    I had an answer saying "The best and probably the accurate description, is that when the gravitomagnetic components due to the spin of the sun and earth are included into the calculations, they shown that the earth is attracted towards the actual position, not the delayed one."
    Is this correct?
  2. jcsd
  3. Nov 19, 2003 #2
    It takes about 8.5 minutes for the light to reach the Earth, so it will have rotated about 8.5/(24*60) of 360 degrees.

    You're thinking of the direction of the electromagnetic attraction due to a charged body (or the gravitational attraction of the Sun). See:

  4. Nov 19, 2003 #3
    from the article:
    what does quadrupole nature of gravitational radiation means[?] [?]
  5. Nov 19, 2003 #4
    It means that the quadrupole moment of the source has to vary in time in order to emit gravitational radiation.

    (A body pulsating in and out spherically, has a time-varying monopole moment. No gravitational radiation -- no electromagnetic radiation from a monopole, either. Two bodies oscillating closer and farther from each other along a line has a time-varying dipole moment -- this would radiate electromagnetically if they were charged, but not gravitationally. But a body being stretched or squeezed asymmetrically, or two bodies orbiting each other, or things like that -- they all have time-varying quadrupole moments and radiate gravitationally.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook