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observations. The basic imaging ideas are the same. Of course, since the wavelength is shorter, mirror surfaces must be more accurate in the ultraviolet than in the visible. The normal coatings that we use to make mirrors reflective in the visible do not work as well in the ultraviolet, and different coatings are needed. Since ultraviolet photons have more energy than visible photons, the uv photons can easily be detected with photographic plates, photomultipliers or CCDs.

The major problem is that ultraviolet radiation does not penetrate the Earth's atmosphere. If you don't go too far into the ultraviolet, some observations are possible at high altitudes. However, we have become increasingly dependent on ultraviolet satellites. Some pioneering satellites were Copernicus (1972-1981) and International Ultraviolet Explorer (IUE, 1978-1996). IUE had a 0.45 m mirror, 3 arc sec angular resolutions and an R = 12 000 spectrograph. Currently, we can use HST, whose mirror was designed to work in the ultraviolet as well as the visible. Far Ultraviolet Spectroscopic Explorer (FUSE) was launched in 1998, with a 0.64 m mirror and a high resolution spectrograph.

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