Our perception of the wavelength of a beam of light can be altered by our velocity relative to the source. This motion-induced change in the observed frequency of a wave is called the Doppler effect . Motion toward the source causes a blueshift . The extent of the shift is directly proportional to the observer's radial velocity relative to the source. Chapter 4 Spectroscopy A spectroscope is a device for splitting a beam of radiation into its component frequencies and delivering them to a screen or detector for detailed study.
Many hot objects emit a continuous spectrum of radiation, containing light of all wavelengths.
A hot gas may instead produce an emission spectrum , consisting only of a few well-defined emission lines of specific frequencies, or colors. Passing a continuous beam of radiation through cool gas will produce absorption lines at precisely the same frequencies as are present in the gas's emission spectrum. Kirchhoff's laws describe the relationships among these different types of spectra. The study of the spectral lines produced by different substances is called spectroscopy . Spectroscopic studies of the Fraunhofer lines in the solar spectrum yield detailed information on the Sun's composition.