Betelgeuse II 
There’s no doubt that Betelgeuse is one of the biggest stars in the galaxy. But just how big is a matter of debate.
The bright orange shoulder of Orion, the hunter, is in the east on December evenings, to the left of the three stars that form Orion’s Belt.
Betelgeuse is a red supergiant — the largest class of stars. Estimates of its size range from about 300 to 500 times the diameter of the Sun. If the larger estimate is correct, then Betelgeuse is big enough to hold more than a hundred million stars the size of the Sun.
Part of the reason for the uncertainty is that the distance to Betelgeuse is also a little uncertain. If you don’t know how far away something is, it’s hard to know how big it is.
But much of the uncertainty comes from the fact that it’s hard to make out the star’s surface.
The outermost layers of Betelgeuse are so thin that they’re not much more than a vacuum. What’s more, the star blows strong “winds” of gas into space. As the gas moves away from Betelgeuse it cools off, so some of its atoms link up to form grains of dust.
The gas and dust form a nebula that extends far into space. So even with the biggest telescopes, it’s hard to tell where the star ends and the nebula begins.
Over time, the material in the nebula — and in the outer layers of Betelgeuse itself — will move out into the galaxy. Some of it may be incorporated into new stars and planets — giving a big star a big role in the life of the galaxy.
Script by Damond Benningfield, Copyright 2011