Quasar, KWAY sahr or KWAY zahr, is an extremely luminous object at the center of some distant galaxies. The word quasar is a shortened form of quasi-stellar (starlike) radio source, a term applied to the first type of quasar identified. Because quasars can resemble stars in our own galaxy in photographs, they are sometimes called quasi-stellar objects. But they are actually among the most distant objects yet detected in the universe. Some are estimated to be as far as 10 billion light-years from Earth. A light-year is the distance light travels in a year, about 5.88 trillion miles (9.46 trillion kilometers). Some quasars shine a trillion times brighter than the sun (see Light-year).