The Chandra X-ray Observatory

The Advanced X-ray Astrophysics Facility (AXAF) was launched in July 1999 as one of NASA's ``Great Observatories'', and was subsequently renamed Chandra, in honor of Subrahmanyan Chandrasekhar. Its prime characteristic is its extremely high spatial resolution. Its X-ray mirrors (consisting of nested shells of grazing incidence optics) are able to resolve angular scales of only 0.2arcsecs. Even with all of the practicalities of observing, resolutions of 0.5arcsec can be achieved. The primary detector array (ACIS) comprises of an array of CCDs at the focal plane of the telescope. When operated in ``imaging'' mode, the X-rays strike these CCDs directly, producing a high-quality image in which the energy of each photon is tagged with moderate energy resolution ($E/\Delta E\sim 50$). In ``spectroscopy'' mode, one of a set of (transmission) diffraction gratings is placed in the X-ray beam, allowing high resolution spectra (up to $E/\Delta E\sim 1000$ at soft X-rays; $E/\Delta E\sim 200$ @ 6keV) to be obtained at the expense of one spatial dimension.