1. Spectroscopy

2. Atoms and Light  Atomic electron energy levels are a source of discrete photon energies.  Change from a high to low energy state produces a photon.  Atoms can also absorb a photon to excite an electron.

3. Discrete Spectrum  Each atom has its own set of energy levels.  Each atom generates photons at specific frequencies.  The pattern of frequencies identifies the atom. helium neon

4. Absorption Lines  Ionized gases at a star’s surface absorb specific frequencies of light.  These appear as dark lines in a star’s spectrum.  Since gases ionize at different temperatures, the appearance of lines indicate the temperature of the star.

5. Molecular Spectra  Energy states in molecules contribute to stellar spectra.  Internuclear distances are quantized in discrete states. Vibrational energyVibrational energy  Angular momentum for the molecule is quantized. Rotational energyRotational energy

6. Fluorescence  Atoms and molecules can reemit absorbed energy.  Fluorescence typically involves three steps. Excitation to higher energy state. Loss of energy through change in vibrational state Emission of fluorescent photon. 10 -15 s S1S1 S0S0 10 -12 s 10 -7 s next