A little bit of History
X-ray astronomy
began with the detection of x-rays from the Sun in 1949, and from
celestial sources outside the solar system in 1962. Unlike optical EM radiation, which we can see, or infrared radiation, which we can feel as heat, X-rays cannot be detected directly by a person. Since their discovery, scientists have refined ways of observing X-rays from outer space. Since X-rays do not penetrate the Earth's atmosphere, instruments to detect them have to be flown on satellites above the atmosphere. X-ray satellites can have instruments that record image data, spectral data, timing data or any combination of the three. Many X-ray satellites observe the same sources, or even the entire sky, over a long time, taking "timing data." Examples of satellites that took timing data, with links to pages on those satellites and their instruments, are:
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