AST 102 Lecture Notes - Lecture 9: 30 Foot Fall, Christian Doppler, Recessional Velocity
Document Summary
Spectroscopy of astronomical objects is the means by which we gain the most information about them. Spectroscopy can also tell us about the relative motion between us and a light source. This is due to something called the doppler effect, named for christian doppler. You all have experienced this, unless you are tone deaf. Think about how the pitch of a train whistle, or a police siren changes as it moves past you. The pitch is high as the source approaches, and then drops when the source passes and begins to move away. The same basic thing happens with light, although the details are different. One can express the doppler effect for light like so: The spectrum of a star is seen to have the balmer lines of hydrogen. But the lines are observed to be at slightly longer wavelength than the bohr formula predicts (and that are observed in the lab).
