Do Now: Stars Spectra

What does the surface color of a star tell us? Explain in detail. Then explain what is an absorption spectra.

Sources of continuous, emission, and absorption spectra

Sources of continuous, emission, and absorption spectra

http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
Thus, emission spectra are produced by thin gases in which the atoms do not experience many collisions (because of the low density). The emission lines correspond to photons of discrete energies that are emitted when excited atomic states in the gas make transitions back to lower-lying levels.

A continuum spectrum results when the gas pressures are higher. Generally, solids, liquids, or dense gases emit light at all wavelengths when heated.

An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum.