section_path: By electromagnetic spectrum/X-ray
section_name: X-ray
paragraph_text: X-ray
  
  X-rays are much harder to collect and focus than electromagnetic radiation of longer wavelengths. X-ray telescopes can use X-ray optics, such as Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect the rays just a few degrees. The mirrors are usually a section of a rotated parabola and a hyperbola, or ellipse. In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror. Examples of space observatories using this type of telescope are the Einstein Observatory, ROSAT, and the Chandra X-ray Observatory. In 2012 the NuSTAR X-ray Telescope was launched which uses Wolter telescope design optics at the end of a long deployable mast to enable photon energies of 79 keV.