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Deneb a supergiant? (APOD 20 Sep 2007)
Posted: Fri Sep 21, 2007 12:29 am
by starnut
The blurb for today's (9/20) APOD says Deneb is a supergiant. So does the web site the highlighted link goes to. I always thought that the term "supergiant" referred to the next to last stage of a massive star's life, e.g., "red supergiant" or "blue supergiant". Is Deneb at that stage? Or is it still in main sequence? If the latter, why not just called it and all other class O, B and A stars "giants" to avoid confusion?
Posted: Fri Sep 21, 2007 12:39 am
by rigelan
Like Betelguese and Rigel, Deneb has to be massively bright in order to be one of our brightest stars here. Betelguese is 400 plus or minus 100 ly away, Rigel is 800 +- 200 ly, and deneb is 3000 +- 1000 or so.
In contrast, Sirius, the brightest star, is 8.6 light years away.
So deneb, in order to be still one of our brightest stars (19th) has to be extraordinarily bright. It is very good assumption to call it a supergiant. And if that means that it will burn out soon, well, quite possibly.