Fig3_12 Doppler effect

Fig3_12 Doppler effect

Fig. 3.12 . A stationary source of radiation (top) emits regularly spaced light waves that get stretched out or scrunched up if the source moves (bottom). Here we show a star moving away (bottom right) from the observer (bottom left). The stretching of light waves that occurs when the source moves away from an observer along the line of sight is called a redshift, because red light waves are relatively long visible light waves; the compression of light waves that occurs when the source moves along the line of sight toward an observer is called a blueshift, because blue light waves are relatively short. The wavelength change, from the stationary to moving condition, is called the Doppler shift, and its size provides a measurement of radial velocity, or the speed of the component of the source’s motion along the line of sight. The Doppler effect is named after the Austrian physicist Christian Doppler (1803-1853), who first considered it in 1842.

Copyright 2010, Professor Kenneth R. Lang, Tufts University