The star at the heart of the swan is a case of “what you see is what you get.” Unlike most of the stars in its weight class, it puts out most of its energy at visible wavelengths. So we see the star in all its glory — across 1800 light-years of space. Sadr represents the breast of Cygnus, the swan, and the center of the Northern Cross, which is outlined by the swan’s brightest stars. It’s a supergiant — the biggest and heaviest class of all stars. Sadr itself is about 12 times as massive as the Sun, and close to 200 times the Sun’s diameter. If it took the Sun’s place in our own solar system, its surface would extend almost all the way out to Earth. Most supergiants shine either blue-white or reddish orange — an indication that their surfaces are much hotter or cooler than the Sun. Most of the radiation from these stars is at wavelengths that are invisible to the human eye — ultraviolet for hot stars, and infrared for cool stars. So while these stars look bright, the eye alone sees onl
