The semi-regular late-type variable supergiant star alpha Orionis, better known as Betelgeuse, pulsating with a period of around 420 days at a distance of 640 light years, one of the largest stars visible to the unaided eye and normally in the top 10 list of brightest stars in the sky, is currently undergoing a rapid dimming event.
If Betelgeuse was located at our sun’s position, it would engulf all the inner planets and extend out to the vicinity of Jupiter’s orbit.
When this star ends its life in a supernova explosion it will be visible in daytime and cast shadows at night.
There have been recent questions about the possibility of Betelguese going supernova (or having done so already) and whether the current dimming may be a sign of it.
ATel 13365 has this to say about the dimming event:
The current faintness of Betelgeuse appears to arise from the coincidence of the star being near the minimum light of the ~5.9-yr light-cycle as well as near, the deeper than usual, minimum of the ~425-d period.
It’s interesting to look at past observations of the star.
Here are the last 2 years of visual and Johnson V observations:
The last 5 years of observations:
The last 10 years of observations:
The last 25 years of observations:
In this and the next plot you can see the transition to image-based photometry about 50 years ago in the form of Johnson V data points.
The last 50 years of observations:
The last 100 years of observations:
It’s apparent that there have been similar dimming events over the last 100 years, e.g. in 1947, 1985 and other years.
It’s not obvious that the current dimming event is significantly more rapid than others that came before it, at least by looking at the slope of a linear fit of dimming events.
Alpha Orionis is a bright star, varying between around magnitude 0 and 1.3. It’s easily observable in the north-eastern late evening sky at the moment, along with comparison stars such as Aldebaran and Pollux.
You can create a finder chart via the AAVSO website. An easier way to get started is to see pages 2 and 3 and the chart on the last page of the AAVSO Citizen Sky southern “10 star” tutorial.
The submission of observations to the AAVSO is encouraged and there’s no need for binoculars or a telescope.