Grazing incidence refers to a specific configuration where light rays hit a mirror at a very shallow angle, typically less than 5 degrees. This design is particularly useful for reflecting X-rays and extreme ultraviolet (EUV) radiation, which are difficult to focus using traditional optical telescopes.

Here's why grazing incidence is used for X-ray and EUV telescopes:

* High reflectivity: At grazing angles, X-rays and EUV radiation experience higher reflectivity than at normal incidence.

* Reduced absorption: With grazing incidence, the radiation interacts less with the mirror material, reducing absorption and allowing for higher transmission.

* Ability to focus: The geometry of grazing incidence allows for the design of mirrors that can focus X-rays and EUV radiation.

Examples of grazing incidence telescopes:

* Chandra X-ray Observatory: One of the most famous X-ray telescopes, Chandra uses grazing incidence mirrors to focus X-rays from distant objects.

* XMM-Newton: Another powerful X-ray telescope that uses grazing incidence optics.

* Solar Dynamics Observatory (SDO): The Atmospheric Imaging Assembly (AIA) on SDO uses grazing incidence telescopes to image the Sun in extreme ultraviolet wavelengths.

In summary, grazing incidence telescopes are specialized telescopes designed to observe X-ray and EUV radiation. They utilize grazing incidence mirrors to achieve high reflectivity, reduced absorption, and the ability to focus these wavelengths.