However, the correlation between types of galaxies and brightness is not so nearly as strong as between types of stars and brightness. Another method employed by astronomers to determine the distances to the distant galaxies is to make use of a fact discovered by the astronomer Hubble. He observed that the farther away a galaxy was, the faster it was speeding away from us. This is the amount colors of light are shifted toward the red. The effect is predicted by the theory of relativity for objects traveling at significant fractions of the speed of light.
Quasars are very bright and very compact and their light is very red shifted.
Exactly what they are is still a mystery. The universe at the distances of the quasars, however, is not like that near our Galaxy. Quasars are billions of light-years from us. This means of course that it took billions of years for the light they emitted to reach us even traveling, as light does, at 186,000 miles per second. Therefore we are observing the quasars not as they appear today but rather as they appeared billions of years ago.