So just what is going on with Betelgeuse?
That’s a good question, and no one seems to have the answer. It may not be possible to have an answer right now.
First of all Betelgeuse is one of my favorite stars in one of my favorite constellations. Betelgeuse is a red super giant star in the constellation Orion. For basic comparison Betelgeuse is 600 times the diameter of the sun and emits 7,500 times the amount of radiation as the Sun. If Betelgeuse were in the Sun’s position the red giant would engulf the planets of the solar system out beyond the orbit of Jupiter.
In the Winter, Orion is clearly visible at night in the northern hemisphere. Betelgeuse is the bright reddish start at the upper end of Orion on the observers left. That is considered the right shoulder of Orion. Just as when you are facing a person, your left side is opposite their right side.
We have all likely been able to see Orion at some time in our lives and are familiar with its shape. A visual aspect of the major stars is shown in the diagram above. There are many more stars in the constellation, but it is these stars that are easiest to pick out when looking up at the constellation at night. Betelgeuse is the star on the upper left. The brightest star in the constellation is Rigel which is opposite Betelgeuse in the lower right side. The other two stars that make up the “frame” of the body of Orion are Bellatrix and Saiph, in the, respectively, upper right position and the lower left position of these four stars.
But discussing the constellation cannot be done without expressing the beauty of the true jewel of Orion, the Orion nebula, the middle star in Orion’s sword that hangs from the three stars of his belt.
Recently there have been numerous articles about the dimming of Betelgeuse. Betelgeuse is a variable star known to dim and brighten over a period of time. However the current dimming is greater than those seen previously. In an article in EarthSky, there is a pair of photographs of Betelgeuse take by Brian Ottum in February 2016 and in December 2019. By comparing the two photographs, the dimming of the star can easily be seen. I found that scaling the picture down in size actually made the difference more apparent.
But can I see this in the sky?
Yes, relatively speaking. Relatively from having seen the star in previous winters as it crossed the sky. Whether out star-gazing on darkened fields, or going out well before sunrise to listen for owls or other birds, I will sit quietly in my folding chair and stare up at the sky. That’s a grand way to spend some time. From this I have a picture in my mind’s eye of the stars in Orion. To me the four stars could be separated as the diagonal pair of Betelgeuse and Rigel, and a second diagonal pair of Bellatrix and Saiph. The stars in these parings have always seemed similar in brightness to me. If you look the stars up you will of course find that the apparent brightness or the absolute magnitude of the two stars in the pairing are not close, but the pairing is the two brighter stars and a second paring of the two less bright stars. To me the diagonal pair of Betelgeuse and Rigel have always been somewhat matched in brightness in the night sky.
After I had seen several articles related to the dimming of Betelgeuse I went out and looked up to see Orion on several nights. But I did not have a picture of what I remembered seeing. I had to recall in my mind how the stars shone. And I could see a difference in Betelgeuse. It was still reddish but it was considerably less bright.
So why the dimming of this inconstant star. Again a good questions and the answer to which will only truly be revealed by the passage of time. Several articles speculated on the shrinking of the giant star as it prepares to blow off its outer shell and explode in a super nova. But I will not need to sit out each night and watch for this as an event like that might not happen for 100,000 years or more. But maybe I will sit out next week and keep my eye on it. That would be a spectacular sight.
However, the light from Betelgeuse takes a over 650 years to reach earth. So, it might have happened already and the light of the event has not yet reached earth.
And recently gravity waves were observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO) that came from the area of the sky in the general area of Betelgeuse. What is that about? In reading information from the American Association of Variable Star Observers (AAVSO) again we do not know the source, but it does not appear to emanate from Betelgeuse.
So we wait to learn. But in the meantime, we can go out on any Winter night and enjoy looking up at the stars of Orion. His frame shines out as does his belt and his sword. The constellation dominates the Winter sky. A bonus are his dogs represented by Sirius and Procyon. And if the night is dark and the sky is clear, below them hiding in the grass you may see Lepus, the rabbit.
The EarthSky article may be found at: https://earthsky.org/space/ligo-gravitational-wave-burst-near-betelgeus
A “tweet” from Dr. Stella Kafka, Director and CEO of AAVSO, on January 14, 2020, may be found by searching at: https://twitter.com