|the branch of astronomy concerned with the detection and measurement of X-rays emitted by certain celestial bodies. As X-rays are absorbed by the atmosphere, satellites and rockets are used|
|a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.|
|a fool or simpleton; ninny.|
The study of celestial objects by measurement of the x-rays they emit. Because the Earth's atmosphere absorbs x-rays, x-ray detectors are usually carried into space on satellites. X-rays are emitted by high-energy objects such as active galactic nuclei, supernova remnants, x-ray binary stars, neutron stars, and the regions around black holes. Objects which do not produce their own x-rays can reflect radiation from nearby stars, making it possible to study the objects using x-ray astronomy; one notable example of this is the analysis of solar x-rays reflected by the Moon.