Early in 2020, Betelgeuse faded to about 30% of its usual brightness.

No pro astronomer was worried it was about to blow. But we still don’t know why it dimmed so much.

Could this have been due to enormous starspots?

Well… maaaaaybe. https://www.syfy.com/syfywire/did-betelgeuse-fade-due-to-supersized-sunspots

2/ The best idea so far is that Betelgeuse belched out a huge cloud of dust that blocked its light. Red supergiant stars do things like this, and B is surrounded by vast clouds of it. But we also know these kinds of stars get spots on them too, like sunspots but hugely huger.

3/ Astronomers observed Betelgeuse in light with MUCH longer wavelengths than the human eye can see: sub-millimeter. The idea is that dust is transparent to it. If dust is the culprit, B should have stayed the same brightness in sub-mm.

But, they saw a 20% drop in light.

4/ They argue that this drop in light must be from the star itself, and the most likely explanation is it has magnetic acne: starspots. They’re darker, so the star dimmed. They find that half of Betelgeuse’s surface may have been covered with starspots.

5/ But… we don’t really know what affects that sub-mm light. There could be other things going on in Betelgeuse’s upper layers to cause it to dim. Starspots *might* be the answer, but it might be something else. In the article I outline more subtle reasons I’m skeptical, too.

6/ At the moment Betelgeuse is back to its “normal” brightness, and its 420-day cycle of brightening and dimming continues. It’ll be pretty interesting to see how it behaves when it starts dimming again soon.

7/7 Stay tuned! Despite being one of the brightest stars in the sky there’s a lot we don’t understand about Betelgeuse. It’s too close to the Sun to see now, but it emerges again in a few weeks. Then we’ll have months to eye it. Keep watching the skies! https://www.syfy.com/syfywire/did-betelgeuse-fade-due-to-supersized-sunspots