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DENEB
Deneb, simply put, is one of the truly great stars of our Galaxy. It serves a three-fold role among the constellations. Its very name tells its first role. "Deneb" is from an Arabic word meaning "tail," as this first magnitude star, the 17th brightest as it appears in our sky, represents the tail of Cygnus the Swan, a classical figure seen flying perpetually to the south along the route of the Milky Way. The reversal of the constellation makes the asterism of the Northern Cross, with Deneb now at the top, the cross seen rising on its side in early northern summer, standing upright in the west in early winter evenings. Deneb also makes the western apex of the famed Summer Triangle, which also incorporates Vega and Altair. All three of these white stars have similar surface temperatures, Vega, at 9500 Kelvin, the warmest. Though Vega and Altair are really quite luminous, they are first magnitude primarily because they are close to us, averaging only 25 light years away. Deneb, on the other hand, may be as far as 2500 light years away. Based on that distance, its awesome luminosity of over 200,000 Suns makes it about the intrinsically brightest star of its kind (that is, in its temperature class) in the entire Galaxy. If placed at the distance of Vega, Deneb would shine as bright as a well-developed crescent Moon. Deneb is a true supergiant, its diameter, calculated from its temperature and luminosity, is 200 times that of the Sun. If it were placed at the center of our Solar System, it would extend to the orbit of the Earth. While far from the largest star in the Galaxy, Deneb is one of the biggest of its kind. It is evolving and has stopped fusing hydrogen in its core. Just what it is doing, however, we do not know. Having begun its life as a star of some 25 solar masses, its fate is almost certainly to explode sometime within the next couple of million years. The star is constant in its light, but its spectrum, its light as seen when stretched into a rainbow, is slightly variable. It is among the most magnificent stars you can see with the unaided eye.