Betelgeuse (Alpha Orionis)

Betelgeuse (Alpha Orionis)

Steve Campbell     December 2015


There is a star in the constellation Orion that is one of the brightest in the sky. You have probably noticed it in the Winter sky and you will see it clearly in the photo in figure A at position 1. I have been reading about this star since I was a young boy in Louisa May Alcott Elementary School. I took an interest in Astronomy at that young an age and I joke that it was because that was the first subject I came to in the library (alphabetical order, you see). Of course, if that were actually the case, I would have more likely been an Anthropologist.

The name of this star is Betelgeuse and I went through life thinking it was pronounced something like “bet tell geese” (with the accent on “bet”). It was not until college that actual Astronomers told me that the proper pronunciation sounds exactly like the words “beetle juice”. You may now recognize the origin of the 1988 Tim Burton movie that starred Michael Keaton, as I did at the time. Betelgeuse is also known by the name “Alpha Orionis” which is derived from its status as the brightest star in the constellation Orion. This is an interesting star for several reasons. All of which I will render unto you readers in the following prose.OrionAnotated

Figure A: The constellation Orion. Betelgeuse is the bright red star at location 1.

Other interesting features of Orion are the “Belt of Orion” – the three stars at location 2, The Orion Nebula (the “blob” near 3) and the blue giant star Rigel at position 4.


Betelgeuse is a type M red supergiant that is much cooler (under 3500 degrees) than the Sun which is a G Type yellow dwarf (5000-6000 degrees). To clear up what a star type is, figure B is a table that explains it. (1).


Figure B: Properties of stars of various spectral types

The alert reader will notice that the average size (radius) of an M type star is only 4% that of our Sun. Betelgeuse is not average, however. It is a Supergiant star whose radius is about one thousand times that of the Sun (2). If you were to replace our Sun with Betelgeuse, it would swallow all planets out to Jupiter. Furthermore its mass is some twenty times that of the Sun, so it would also draw in the remaining planets.

But, such projects as replacing the Sun with Betelgeuse can only be contemplated by Big Government and such a program will no doubt be cancelled – perhaps when someone realizes that the Earth is one of the planets to be consumed. As is typical, they will have spent tens of billions and accomplished nothing. So, it is not something to worry about.

Betelgeuse is only about ten million years old but is nearing the end of its lifetime. Very large stars like this burn through their fuel much faster than dwarf stars like the Sun. By the way, the Sun’s actual name is “Sol” (the “o” is long). Anyway, Sol is about four and a half billion years old and will live on for billions of years. The prognosis for Betelgeuse is, alas, rather grim. It is expected to die off in less than a million years. Already the decline has become apparent.

The accurate measurement of actual star diameters has become possible with larger and more advanced telescopes, One advance is called “adaptive optics” that changes the shape of the mirror to better focus the light which is distorted by atmospheric conditions. Space telescopes represent another advance that does away with the atmospheric problem altogether. Betelgeuse has been measured repeatedly and has been found to be shrinking. From 1993 until now, it is estimated to have lost 15% of its diameter. Figure C has an actual photo (made possible by those advances of which I spoke) of Betelgeuse on the left and a copy that I have adjusted to be 15% smaller on the right. You can see that the reduction is a significant amount. The difference is, in fact about 127 million miles (205 million km.). For comparison, the distance from the Earth to the Sun is about 93 million miles (150 million km.).


Figure C: A photo of Betelgeus (left) and a copy that is 15% smaller (right).


However, Betelgeuse will not go gentle into that goodnight. Stars that are above a certain size end their lives in a Supernova – a spectacular explosion. Such will be the fate of Betelgeuse. A star’s energy comes from fusion of lighter elements into heavier ones. Hydrogen fusing to make helium is the first, simplest and most energetic of these. When all of the hydrogen is exhausted, and the star is massive enough, helium can fuse to make carbon, and so on. There is energy to be gained in all fusion up to the element Iron. After that, it takes external energy to make heavier elements. When a star can no longer fuse elements, its core will collapse and then the immense heat of compression will result in the aforementioned explosion. It also creates heavier elements like -to mention a well known few – Copper, Silver, Gold, Mercury and Uranium. Supernovae (yes, that is the correct plural) are the only sources of these elements and so, you see that the earth is made of recycled materials.

The explosion will be visible from Earth as Betelgeuse will quickly brighten to rival or surpass the moon in our skies. This will last a few years and Betelgeuse should actually be visible in the daytime sky. All this has happened before (with other stars, of course) and been recorded in history, but not lately. While the Supernova will be a caldron of intense radiation, we are some 640 light years from Betelgeuse and should not feel any ill effects.


Betelgeuse will someday end its life in a spectacular explosion. It may be anytime in the next million years. Indeed, it may already have happened and the light from it will arrive here 640 years after the event. That is not very likely, however.

Betelgeuse may actually outshine the rest of the Galaxy, briefly and be visible in the daytime sky for months or years. It will release more energy, in that time than our sun will put out in its entire lifetime. We should not be harmed physically by the arrival of that radiation, because it will be severely attenuated by the distance and the Earth is also shielded by its magnetic field. There is a subsequent wave of slower, but also radioactive particles that will arrive much later. I don’t know much about those yet, but when I find out, I’ll let you know.


  1. Star Type Classifications:
  2. Betelgeuse Statistics:
  3. Supernova details:

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