On the left shoulder of the constellation Orion lies Alpha Orionis, a red giant with an apparent magnitude of 0.7. Betelgeuse is, in every sense, a huge and brilliant star—about 14,000 times more luminous than our Sun and the ninth-brightest star in the night sky.
Don't be misled by that seemingly modest ninth-place ranking. The reason is its enormous distance: roughly 650 light-years. Think about those numbers—650 light-years away, yet still magnitude 0.7. Compare that with Sirius, the brightest star in the night sky, at magnitude -1.6 and only about 8.7 light-years from Earth.
If this supergiant were a little closer, we would appreciate its scale much more dramatically. Imagine swapping the positions of Betelgeuse and Sirius. If Betelgeuse occupied the place of our stellar neighbour Sirius, it would appear about as large and bright as the full Moon and could even be seen during the day—roughly 400 times brighter than it appears now. That might make life somewhat difficult for us Earthlings!
So what is all the fuss about?
I don't want to take the discussion beyond a simple level. Put plainly, Betelgeuse is dying—but the death of a star like this is hardly a quiet affair.
Let's play another imaginary game and replace our Sun with this red giant. This time we would have a very serious problem. If Betelgeuse stood where the Sun is, not only Mercury and Venus but Earth itself, along with Mars and at times even Jupiter, would lie inside Betelgeuse. Why “at times” for Jupiter? Because Betelgeuse is an irregular variable star whose diameter, over a period of five to six years, varies from about 500 to 750 times the diameter of the Sun.
Even all of that describes only its outward appearance. Despite its enormous size, the star is extremely diffuse: with a mass of only about twenty Suns, it is one of the least-dense stars.
These days Orion is still hunting across the turning dome of the sky, but soon it will disappear into the brightness of daytime. While there is still time, look at it in the night sky with a different perspective. And once again we can be thankful that this restless red giant lies so far away that it cannot cause us the slightest harm—a small glimpse of the grandeur of creation across the universe.
I also recommend listening to Episode 156 of Astronomy Cast to hear more about Betelgeuse and several other famous stars, and watching the clip included with the original post.
Additional Original Article Links [source]
