blauverschoben

Blauverschoben is the German term for light that is blue-shifted, meaning its observed wavelength is shorter than the emitted wavelength. This effect is primarily caused by the Doppler shift when the source moves toward the observer, but can also arise from gravitational effects in general relativity, such as light moving into a gravitational potential well. In astronomy, a blue shift indicates a source with a nonzero line-of-sight velocity toward the observer.

Quantitatively, for small velocities v much less than the speed of light, the fractional change in wavelength is approximately Δλ/λ ≈ -v/c, so the observed wavelength is λ_obs ≈ λ_emit(1 - v/c). For high speeds, the relativistic Doppler formula applies: the observed frequency f_obs = f_emit √((1 + v/c)/(1 - v/c)), which implies λ_obs/λ_emit = √((1 - v/c)/(1 + v/c)). A negative Δλ/λ corresponds to a blue shift, while a positive one corresponds to a red shift.

Observationally, blue shifts are most common for nearby objects that move toward the observer, such as certain binary stars or material in active galactic nuclei whose near-side components are directed toward Earth. In cosmology, most distant galaxies show redshift due to the expansion of the universe; blueshifted objects are relatively rare and typically local or gravitationally influenced. Gravitational blueshift occurs when photons gain energy falling deeper into a gravitational well, such as near massive compact objects.

See also: redshift, Doppler effect, spectroscopy, radial velocity.