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A hot and dense (or high pressure) gas will produce a continuous spectrum.

Kirchhoff’s Gas Laws # 1. A hot and dense (or high pressure) gas will produce a continuous spectrum. Kirchhoff’s Gas Laws #2. Passing light through a thin gas will produce an absorption spectrum of many different lines.

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A hot and dense (or high pressure) gas will produce a continuous spectrum.

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  1. Kirchhoff’s Gas Laws #1 A hot and dense (or high pressure) gas will produce a continuous spectrum.

  2. Kirchhoff’s Gas Laws #2 Passing light through a thin gas will produce an absorption spectrum of many different lines. Which ‘colors’ are missing depends on what elements or molecules the gas is made of.

  3. Quantum Mechanics tells us that electrons can only orbit atoms at certain distinct levels

  4. N=5 N=4 N=3 N=2 N=1 These levels correspond to different amounts of electron energy, and are different for each element of the Periodic Table.

  5. N=5 N=4 N=3 N=2 N=1 If a photon with exactly the right amount of energy hits an electron, the electron will jump to a higher level.

  6. N=5 N=4 N=3 N=2 N=1 Other specific energies (or colors) will excite the electron to other energy levels.

  7. N=5 N=4 N=3 N=2 N=1 Whether or not (and to where) an electron will jump depends on: 1.) Which element the atom is, and 2.) Whether the photon has just the right amount of energy to bridge a gap. Notice that the second ‘blue’ photon did nothing. The electron was already in the second level.

  8. N=5 N=4 N=3 N=2 N=1 A photon is usually emitted immediately, though.

  9. Kirchhoff’s Gas Laws #2 Atoms thus appear to absorb energy, and the resulting spectrum has ‘absorption lines’

  10. Photons may scatter many times before leaving a nebula

  11. This doesn’t happen to just one color of light; all light from the source passes through the cloud.

  12. Kirchhoff’s Gas Laws #2 The cool outer layers of stars also produce absorption lines, so we can see what stars are made of.

  13. Kirchhoff’s Gas Laws #3 If we remove the star and assume the gas itself is hot and excited, we get an emission spectrum.

  14. In this case, heat energy is being converted into light

  15. Kirchhoff’s Gas Laws #2 Remember that light is always re-emitted… so where did the absorbed light in this case go? It lights up the rest of the nebula, which we couldn’t see otherwise

  16. Absorbed energy can also be transferred back into heat and between atoms.

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