Perhaps nothing better illustrates the movement toward more and more precise spectra since the advent of x-ray astronomy 40 years ago than looking at the results. The following spectrographs were all taken of a star named Capella, which is 42 light-years away and shines in northern skies.

The first spectrum taken of Capella was made during a rocket flight in 1974, and this spectrograph was published in March 1975.

By the HEAO-1 mission, launched in 1977, spectrographs had advanced considerably, as you'll see in this example.

HEAO-2, also called "Einstein," was launched in 1978 and was the first imaging x-ray mission--which gave astronomers the ability to "see" what they were measuring. Einstein was also better at separating the background radiation from the actual object than previous instruments.

Today, with Chandra, launched, two years ago, astronomers are able to separate individual emissions "almost" within a line--untangling blended data better than ever before. Here is the total range and one that demonstrates several components (r, i and f) of one emission line--used to derive temperature, density and ionization of gases in and around an object of study. Last, an XMM-Newton spectrograph. --Ilana Harrus

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