http://www.rssboard.org/rss-specification 720 http://ecuip-xtf.lib.uchicago.edu/xtf/search?expand%3Dspectral-Type;f1-spectral-Type%3DOptical;f2-facility%3DDigitized%20Sky%20Survey Results for your query: expand=spectral-Type;f1-spectral-Type=Optical;f2-facility=Digitized Sky Survey Thu, 01 Jan 1970 12:00:00 GMT http://ecuip-xtf.lib.uchicago.edu/xtf/view?docId=grxr/cygx1_optical/cygx1_optical.dc.xml Since its discovery in 1962, the X-ray binary star Cygnus X-1 has been one of the most intensively studied cosmic X-ray sources. About a decade after its discovery, Cygnus X-1 secured a place in the history of astronomy when a combination of space-based, X-ray observations by the Chandra X-ray Observatory and optical, ground-based observations by the Digitized Sky Survey led to the conclusion that it was a black hole, the first such identification. This is an optical image of Cygnus X-1. http://ecuip-xtf.lib.uchicago.edu/xtf/view?docId=grxr/cygx1_optical/cygx1_optical.dc.xml Thu, 01 Jan 1970 12:00:00 GMT