<P> Knowledge of redshifts and blueshifts has been applied to develop several terrestrial technologies such as Doppler radar and radar guns . Redshifts are also seen in the spectroscopic observations of astronomical objects . Its value is represented by the letter z . </P> <P> A special relativistic redshift formula (and its classical approximation) can be used to calculate the redshift of a nearby object when spacetime is flat . However, in many contexts, such as black holes and Big Bang cosmology, redshifts must be calculated using general relativity . Special relativistic, gravitational, and cosmological redshifts can be understood under the umbrella of frame transformation laws . There exist other physical processes that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects; however, the resulting changes are distinguishable from true redshift and are not generally referred to as such (see section on physical optics and radiative transfer). </P> <P> The history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect . The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842 . The hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845 . Doppler correctly predicted that the phenomenon should apply to all waves, and in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth . Before this was verified, however, it was found that stellar colors were primarily due to a star's temperature, not motion . Only later was Doppler vindicated by verified redshift observations . </P> <P> The first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect . The effect is sometimes called the "Doppler--Fizeau effect". In 1868, British astronomer William Huggins was the first to determine the velocity of a star moving away from the Earth by this method . In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red . In 1887, Vogel and Scheiner discovered the annual Doppler effect, the yearly change in the Doppler shift of stars located near the ecliptic due to the orbital velocity of the Earth . In 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors . </P>

Who was the first to notice that distant galaxies were red shifted with respect to closer stars