1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Spectral lines and absorption lines

  1. Mar 18, 2013 #1
    On PF, to answer why atmosphere is transparent, users explained that atmospheric gases such as oxygen do not have absorption lines in the visible spectrum. On UColorado website, under Spectral Lines, they show that Oxygen has many visible lines in its spectral signature. This confuses me, because I thought absorption lines and an atom's spectral signature lines are the same frequencies, so the information seems to be conflicting.
  2. jcsd
  3. Mar 18, 2013 #2
    Note that most of the atmosphere is Nitrogen, not Oxygen. Also note that the Nitrogen and Oxygen in the atmosphere are not lone atoms, but diatomic molecules (O2 and N2). Molecule's lines are not the same as its constituent atom's lines. I know this doesnt answer your question, but I would see if you can find O2 and N2's lines.
  4. Mar 20, 2013 #3
    If the gases in air, mainly N2 and O2, did not have absorption lines in the visible spectrum, this would solve my question. However on http://en.m.wikipedia.org/wiki/Spectral_line
    Spectral lines for air is shown to have many lines in visible light, so I am still not sure...
  5. Mar 21, 2013 #4


    User Avatar
    Homework Helper

    Absorption and emission lines are of different intensity. The molecules of the atmosphere do not have first-order absorption lines in the visible range, but do have weak ones, mainly the qxygen and water molecules. So a layer of air even about one metre thick is transparent but the sunlight is a bit absorbed at certain frequencies/wavelength when traversing the whole atmosphere.

    Last edited: Mar 21, 2013
  6. Mar 22, 2013 #5
    does this means that air has strong absorption lines in the electromagnetic spectrum outside of the visible light?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook