Using the equation for the Doppler effect (wavelength and radial velocity), the student is asked to compare a standard wavelength against measured wavelengths in order to determine if the orbiting body has negative/positive radial velocity (a convention) and if it's moving toward or away from the Earth.
keywords: radial velocity, wavelength, Doppler effect, convention
swf file: ca_extrasolarplanets_dopplersign.swf