Redshift and blueshift describe the change in the frequency of a light wave depending on whether an object is moving towards or away from us.
Both redshift and blueshift are determined by studying the spectrum of light radiated from the object. Specifically, "fingerprints" of elements in the spectrum (which is taken with a spectrograph or a spectrometer), are "shifted" toward the blue or red depending on the motion of the object. ...
The Doppler redshift of light observed from stars and galaxies provide evidence that the universe is expanding such that it is moving away from a central point. This makes the Big Bang Theory as after the bang occurs all the matter moves away from the point of origin or their central point...
Astronomy is the scientific study of all objects in space. The word comes to us from the ancient Greek term for "star law." Astrophysics, which is part ofastronomy, goes a step further and applies thelaws of physicsto help us understand the origins of the universe and the objects in it....
It may be a convention fo some but that does not make it any way true. The issue is simple and directly related to the principle of equivalence in general...