At the high-energy end of the electromagnetic spectrum, x rays provide a unique window on some of the hottest and most violent objects in the universe. Since the discovery of extra-solar x-ray sources in 1962, scientists have investigated a large number of phenomena which emit x rays. With each new space mission, more sources and more details of the structure of the xray universe have been gleaned.
Although they are among the most energetic of the electromagnetic spectrum, and thus provide a window on some of the most violent processes in the universe, x rays are not able to penetrate Earth's atmosphere; they are absorbed at about 62 mi (100 km) above the surface. Thus, only with the advent of rocket and satellite astronomy have astronomers been able to study the wide-ranging phenomen…
Although the temperature of the sun's surface is about 6,000K (10,341°F; 5,727°C), by the 1930s there was evidence that the outer regions of the solar atmosphere were much hotter, meaning that they could be a source of x rays. At that time there was no way to verify this prediction, however. After World War II, when captured V-2 rockets allowed scientists to place instruments …
A wide variety of x-ray sources have been seen since the first extrasolar identification in 1962. A few of the most interesting types of sources are: The Sun. A number of x-ray satellites have monitored the Sun. Solar flares produce enhancements in its x-ray output. Stars. Many stars, particularly those with coronae or rapid stellar winds, emit x rays from their outer layers. Comets. Astronomers h…
Among the largest and most productive x-ray missions were Uhuru (1970), which catalogued 339 x-ray sources; Einstein (also known as HEAO-2, 1978-1981); and EXOSAT (1983-1986). In addition, there have been many smaller-scale observations. The more recent missions, such as the German ROSAT (Röntgensatellit), launched in 1990, contain very sophisticated instrumentation, including detectors and…
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