Chandra Observatory is the third of NASA's four "Great Observatories". The first was Hubble Space Telescope; second the Compton Gamma Ray Observatory, launched in 1991; and last is the Spitzer Space Telescope. Prior to successful launch, the Chandra Observatory was known as AXAF, the Advanced X-ray Astronomical Facility.
Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes, requiring a space-based telescope to make these observations. Unlike optical telescopes which possess simple silvered parabolic surfaces (mirrors), X-ray telescopes generally have nested parabolically cylindrical surfaces coated with iridium. With an angular resolution of 0.5 arcsec, Chandra possesses a resolution over one thousand times better than the resolution of the first orbiting X-ray telescope, which had less precise gold-coated mirrors. A diffractive grating provides excellent spectral resolution compared to older X-ray missions, about 1 in 1000. Chandra can also detect variations in X-ray emissions as short as 17 microseconds. The data gathered by Chandra have opened a new field in astronomy, shedding light not only upon our own Galaxy (the Milky Way), but many other galaxies and galaxy clusters.
Some objects observed with the Chandra Observatory include: