Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.X-ray emission occurs from many celestial objects. These emissions can have a pattern, occur intermittently, or as a transient astronomical event. In X-ray astronomy many sources have been discovered by placing an X-ray detector above the Earth''s atmosphere. Often, the first X-ray source discovered in many constellations is an X-ray transient. These objects show changing levels of X-ray emission. NRL astronomer Dr. Joseph Lazio stated: ... the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths, ... . There are a growing number of recurrent X-ray transients. In the sense of traveling as a transient, the only stellar X-ray source that does not belong to a constellation is the Sun.