The decrease in wavelength of electromagnetic radiation from a source moving toward the observer, causing the light to appear shifted toward the blue end of the spectrum. This is the opposite of redshift and indicates approach rather than recession.
Coined in the mid-20th century as the counterpart to 'redshift,' combining 'blue' (representing shorter wavelengths) with 'shift.' The term emerged as astronomers developed more sophisticated spectroscopic techniques to measure stellar motions.
While most of the universe shows redshift due to cosmic expansion, blueshift reveals objects bucking the trend! The Andromeda Galaxy is actually blueshifted because it's racing toward us at 250,000 mph - we're on a collision course in about 4.5 billion years.
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