manifestation of the Doppler Effect
emitted by an object as that object moves towards the observer, as opposed to the red shift
observed when an object is moving away.
When an object is moving towards the observer, the object's electromagnetic spectrum
is shifted towards the blue end of the electromagnetic spectrum
. Thus, blue shift can be detected by analyzing emission lines
and absorption lines
in the spectra
of astronomical objects that are moving toward the Earth, and comparing them to the spectra of objects of similar chemical composition. (For example, a rotating object displays blue shift on one side, and red shift
on the other).
The faster an object approaches the observer, the more the radiation emmited by the object is shifted: microwave
s become infrared
, infrared becomes visible light
, visible light turns into ulraviolet
, ultraviolet becomes X-ray
s, X-rays become gamma ray
Not only are emission and absorption lines shifted, the object's overall electromagnetic frequency distribution
due to black body
radiation is also shifted. To an osberver, an approaching object is hotter
than one that is stationary relative to the object, or moving away!
Due to the expansion of the universe
, as well as the fact that other effects besides motion cause observable red shift, objects exhibiting blue shift are much harder to find than ones exhibiting red shift.