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

I Light and our atmosphere (some quantum physics)

  1. Jun 27, 2016 #1
    I was looking at the moon rising and noticed that it starts off quite yellow/orange and gets more and more white as it reaches the middle of the sky.
    Why does it look bigger? I'd imagine it's something to do with refraction, but how exactly does it work?
    Does the moon look more orange closer to the horizon because the light to reach it took a longer path through our atmosphere, and, therefore, more blue light/UV light has been absorbed/scattered and so more light in the lower energy spectrum reaches the moon? I thought of this since it appears white in the middle of the sky, where almost no light reaching it has passed through our atmosphere (ignoring the light that came back from it to hit earth)
    Oh and it to my assumption, since our ozone blocks light in the UV/UVB range, does that mean it will also block some bluer/purple light?

    Does the sky look blue because the molecules that make up our atmosphere let lights through and absorbs some of the blue light and re-emits everywhere, making it so the sky appears to be blue?
  2. jcsd
  3. Jun 27, 2016 #2


    User Avatar
    Science Advisor
    Gold Member

    You're correct on both counts - reddening of the Moon and the Sun as well as the blue hue of the sky are all caused by scattering in the atmosphere. The following article explains it in depth:

    The apparently larger moon over the horizon is an optical illusion. There's no actual difference in measurements (it's actually a tiny bit smaller over the horizon, since it's farther away). I've seen a number of explanation for the illusion, but since it's a matter of psychology, its hard to make ironclad statements about the underlying reasons.

    Ozone vibrational modes absorb most strongly in infrared (so it's a greenhouse gas); its UV-absorbing capacity comes from the formation/breakup cycle involving UV and oxygen.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted