David - Doppler He is known for the principle he proposed he first proposed in concerning the colored light of double stars in He hypothesized that the pitch of a sound would change if the source of the sound was moving. The Doppler Effect named after Christian Doppler it work with light waves. Also the effect to determine that the universe is expanding, Hubble found that light from distant galaxies is shifted toward higher frequencies known as red Doppler shift.

David – Doppler Spectral lines of stars that are moving toward an observer shift toward shorter wavelength or are blue shifted.