Astronomical Spectroscopy - Mechanisms

Mechanisms

Stars emit light at all frequencies in the core; molecules, atoms, and ions that may be present near the surface of the star will absorb strongly at certain characteristic frequencies. Thus the observed spectrum will contain relatively dark bands at the characteristic frequencies of constituents of the outer layers. Absorption spectra of nebulae and planetary atmospheres arise simply when molecules absorb light of from the parent star and re-emit it in random directions and at different frequencies.