Orion is one of the more identifiable constellations in the night sky. The set of stars is often depicted as a swordsman, with three stars making up the belt, three the sword, and four the shoulders and knees. Marking the right shoulder is the star Betelgeuse, a red supergiant.

On December 8th 2019, measurements of Betelguese’s brightness showed that the star had dimmed slightly. Repeated measurements on December 23rd showed further dimming. Betelguese is usually the 9th brightest star in the ski, but has dropped to the 20th brightest. The star’s brightness has been measured for 25 years, and these measurements marked the dimmest it has been during that time. Measurements of the stars color, which can be converted to the surface temperature, showed cooling of 150oC.

So what is happening to Betelguese? Is this dimming a sign of a star on its last legs? Betelguese will one day end its life as a supernova. The star will dim as it runs out of fuel before bursting into an extremely bright supernova as it collapses in on itself. If anybody is watching from earth, it will show up as bright as the moon in the night sky. Betelguese will launch a bunch of matter into space at this point, but any observers need not worry about that, because the matter will take several million years to reach earth and will then be stopped by the activity of our own sun.

Don’t say goodbye to Orion quite yet though. Betelguese isn’t expected to go supernova for about 100,000 more years. This dimming is more likely due to natural dimming cycles of the star. For reasons that astronomers don’t fully understand, Betelguese seems to have cycles where is dims and brightens about every 425 days. There is a secondary, less dramatic dimming cycle that takes 5.9 years. Right now, the star is near the dim period of both cycles, possibly leading to the unusually extreme dimming. If this is the case, Betelguese will shortly start to brighten again very soon. In the meantime, the dimmer star gives scientists an opportunity to study its properties and collect measurements of its behavior during dim periods.


Corresponding Author: Emily Kerr

Original Scientific Reports: 

The Fainting of the Nearby Red Supergiant Betelgeuse

Updates on the “Fainting” of Betelgeuse

Popular Press Article: When Will Betelgeuse Explode?  

Image Credit: Rogelio Bernal Andreo


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