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Stars twinkle, but planets don't?

  1. Feb 25, 2008 #1
    Hello everyone - newbie here. Am I right to say that stars twinkle because of regions of the atmosphere being at different (and varying) temperatures and pressures etc., giving rise to a variation in refractive index and consequently a shifting image of the observed object? If so, why don't I observe planets to do the same thing? I thought it might be because planets appear much brighter, but then don't some stars shine more brightly than some planets at times? Thanks.
  2. jcsd
  3. Feb 25, 2008 #2


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    Stars twinkle because of the movement and different temperatures in the atmosphere cause the light to refract. You have that part right, the reason that planets do not seem to twinkle (I have seen Saturn twinkle when close too the horizon) is not due to the brightness but it is due to the size of the image. Stars are point sources and planets have some size too them.
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