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Blue shift is an astronomical term referring to the shortening of a transmitted signal’s wavelength that may, or may not, be accompanied with an increase in frequency. This is due to the relativistic Doppler effect and indicates that the object is moving towards the observer. The name ‘blue shift’ is derived from the fact that the shorter-wavelengths of the optical spectrum is blue portion of light. Only the most distant galaxies and those moving at speeds far above average emit light that arrives with a perceptible blue tinge.
These are only a few known possible causes of blue shift in astronomy. One is the movement of a light source towards the observer. This can be the edge of a rotating galaxy, blazars(very compact quasar) propelling relativistic jets, and some specific quasars. There are some gravitational effects that cause blue shift also. For this aspect a certain wavelength originating from a source placed in a region of stronger gravitational field(coming uphill from a gravity well) will be found to be of longer wavelength when received by an observer in a region of weaker gravitational field.
Red shift is much more better known in modern astronomy. The red shift of starlight is thought to be evidence of an expanding universe, but there are a few examples of blue shift in astronomy. The Andromeda Galaxy is moving towards within the Milky Way galaxy, so when it is observed from Earth, its light is blue shifted. Barnard’s Star is also moving towards us and appears to have a slight blue shift.
If you are interested in researching blue shift, then you should also spend some time reading about Tully-Fisher relation, blazars, relativistic jets, synchrontron radiation, Bremsstrahlung. This is a little understood occurrence that warrants a lot of research.
We’ve also recorded an entire episode of Astronomy Cast all about the Doppler Effect. Listen here, Episode 165: Doppler Effect.