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Blue shift is the phenomenon that the frequency of an electromagnetic wave (such as light) emitted by a source moving towards the observer is shifted towards the blue end of the spectrum (that is, its wavelength is decreased).

The phenomenon of shifting wavelengths in frames of reference moving relatively to each other is commonly known as Doppler shift or Doppler effect.

While the general redshift of starlight is seen as proof for an expanding universe, there are few examples of blue shift in astronomy:

The Andromeda Galaxy is moving towards our own Milky Way Galaxy within the Local Group; thus, when observed from earth, its light is undergoing a blue shift.

When observing spiral galaxies, the side spinning towards us will have a slight blue shift (see Tully-Fisher relation).

Also, Blazars are known to propel relativistic jetSee also: Jet (disambiguation A jet is a stream of fluid produced by discharge through an orifice into free space. Since gases are compressible fluids, the velocity attained by a jet of gas cannot be determined by Bernoulli's principle. Instead, if one uss towards us, emitting synchrotron radiationSynchrotron radiation refers to electromagnetic radiation similar to cyclotron radiation, but generated by electrons moving at highly relativistic speeds. Synchrotron radiation can be generated by astronomical structures and motions. See also synchrotron and BremsstrahlungBremsstrahlung German for braking radiation, is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. The term is also used to refer to the that appears blue shifted.

See also

• Doppler effect
• redshift
• theory of relativityAlbert Einstein's theory of relativity is a set of two theories in physics: special relativity and general relativity. The core idea of both theories is that two observers who move relative to each other will often measure different time and space interva

Blue ShiftBlue Shift is the tenth story chronologically to appear in Stephen Baxter's science fiction anthology novel Vacuum Diagrams . Blue Shift" was originally published in Writers of the Future volume 5 in 1989. Set in A. 5406, the story begins on an Earth that is also the title of a story by Stephen Baxter.