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Does sunlight push the Earth ever so slightly?

  1. Sep 22, 2006 #1
    Considering that the Sun radiates EM photons at many different wavelengths onto the Earth and that these photons carry a momentum which they impart into the Earth upon contact, wouldn't the aggregate of all these 'pushing' photons create a noticeable effect on the the Earth's graviational orbit around the sun? I wonder about the intensity of this radiation pressure in proportion to the intensity of sun's graviational effect. Since alot of our estimate as to what the Earth's interior composition is based on inferred knowledge of the Sun's mass and the moon's mass we should take into account the radiation pressure's effect which pushing our orbit further out from the sun than if the sun suddenly went 'lights out!' but its mass remained constant in the dark blackness.
  2. jcsd
  3. Sep 22, 2006 #2
    theoretically yes but i doubt itd be noticeable as both the forces inquestion (photon pressure and gravity) are very weak
  4. Sep 22, 2006 #3

    Meir Achuz

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    It's relatively easy to calculate the radiation force, and it is negligible.
    The pressure =2Icos\theta/c (Gaussian units) for reflected sunlight
    (Icos\theta/c if s\absorbed). I=12X10^5 ergs/cm^2-sec at the Earth's surface.
  5. Sep 22, 2006 #4

    Andrew Mason

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    The radiation pressure as well as the solar wind tends to push the earth outward and thereby increase its energy. But the motion of the earth through the solar wind causes loss of energy and tends to slow the earth down a bit. I suspect that these very small forces almost cancel each other out.

  6. Sep 22, 2006 #5


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