On the coloured light of the binary stars and some other stars of the heavens

On the coloured light of the binary stars and some other stars of the heavens or in the original German Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels is a treatise by Christian Doppler (1842)[1] in which he postulated his principle that the observed frequency changes if either the source or the observer is moving, which later has been coined the Doppler effect.

The title "Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels - Versuch einer das Bradley'sche Aberrations-Theorem als integrirenden Theil in sich schliessenden allgemeineren Theorie" (On the coloured light of the binary stars and some other stars of the heavens - Attempt at a general theory including Bradley's theorem as an integral part) specifies the purpose: describe the hypothesis of the Doppler effect, use it to explain the colours of binary stars, and establish a relation with Bradley's stellar aberration.

Proponents claim this is necessary to explain polarised light, whereas opponents object to implications for the aether.

§ 2 Doppler observes that colour is a manifestation of the frequency of the light wave, in the eye of the beholder.

He thinks, without reason, that a confirmation of his theory would imply that light is not a transverse but a longitudinal wave.

§ 9 Doppler notes that the orbital speed of the Earth (4.7 Meilen/s) is too low (<33 Meilen/s) to result in visually perceptible colour changes.