- X-rays cannot be focused by conventional lenses and mirrors. So telescopes for X-ray astronomy depend on unusual technology. The most common design makes use of grazing incidence, in which the X-rays are reflected at a low angle from a succession of surfaces of some material which does not absorb them, bringing them gradually to a focus to form the image. New materials may allow genuine X-ray lenses and mirrors to be made. In addition, it is now proving possible to make X-ray telescopes of conventional design by using mirrors made of thin sandwiches in which light and heavy atoms alternate. These materials reflect X-rays as glass reflects light.
- A telescope which detects, amplifies, and analyses the X-ray emissions of celestial bodies. Since the atmosphere absorbs X-rays, observations must be performed above a given altitude, such as 100 kilometers, using satellites or rockets, and orbits may range past 100,000 kilometers.