Chandra image of Cygnus X-1

Cygnus X-1 is one of the brightest X-ray sources seen from Earth. It was one of eight sources discovered during a sounding rocket flight in 1964. The rocket carried instruments to detect celestial sources of X-rays. The name "Cygnus X-1" tells us that the source is the brightest X-ray source within the Cygnus constellation. It us usually shortened to "Cyg X-1."