or blue shift
a shift toward shorter wavelengths of the spectral lines of a celestial object, caused by the motion of the object toward the observer.
Origin of blueshift
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a shift in the spectral lines of a stellar spectrum towards the blue end of the visible region relative to the wavelengths of these lines in the terrestrial spectrum: a result of the Doppler effect caused by stars approaching the solar systemCompare redshift
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012