# Betelgeuse losing brightness **URL:** \ **Category:** Factual Questions\ **Created:** [December 27, 2019, 11:34pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478 "2019-12-27T23:34:54Z")\ **Posts on this page:** 11\ **Page:** 12
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [September 5, 2026, 5:51am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/222 "2026-09-05T05:51:22Z")
> **[Betelgeuse's atmosphere is becoming spotty and asymmetric—and a nearby...](https://phys.org/news/2026-09-betelgeuse-atmosphere-spotty-asymmetric-nearby.html)** > > For the first time since its dramatic dimming in 2020, a team of astronomers has observed the inner atmosphere of Betelgeuse using the Atacama Large Millimeter Array (ALMA). Led by Bill Dent at the University of Manchester, the team found that the... ---
**Author:** ![Fiendish\_Astronaut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiendish_astronaut/32/3295_2.png) [@Fiendish\_Astronaut](https://boards.straightdope.com/u/Fiendish_Astronaut)\ **Post date:** [September 8, 2026, 8:18pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/223 "2026-09-08T20:18:17Z")
I find it incredible that a star with a life span measured in the millions of years can appear to change so much in less than a decade. ---
**Author:** ![Zakalwe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zakalwe/32/270_2.png) [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)\ **Post date:** [September 8, 2026, 10:47pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/224 "2026-09-08T22:47:59Z")
I don’t know that it changed so much as that our ability to detect changes over the expected values increased over the course of that decade. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 8, 2026, 10:56pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/225 "2026-09-08T22:56:31Z")
We’ve long had the ability to detect changes like the one that prompted this thread. In fact, that change was obvious even to the naked eye. What’s lacking going back to antiquity is good records, not the observation technology itself. While we’re at it, Betelgeuse is officially designated “alpha Orionis”, meaning the brightest star in Orion. Or at least, that’s what it meant at the time the names were assigned. It’s been dimmer than Rigel for all of the photometric era. ---
**Author:** ![Zakalwe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zakalwe/32/270_2.png) [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)\ **Post date:** [September 8, 2026, 11:18pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/226 "2026-09-08T23:18:10Z")
Okay. I was mostly going off the more recent articles about actually being able to see the surface changes. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [September 9, 2026, 12:12am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/227 "2026-09-09T00:12:40Z")
Betelgeuse might already have gone Nova, what we see today is some 640 years in the past- and it could be as bright as the full moon. But it is not likely to go nova in our lifetimes, but relatively soon, as these things go. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [September 9, 2026, 12:50am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/228 "2026-09-09T00:50:28Z")
> [@DrDeth](#): > > Betelgeuse might already have gone Nova, what we see today is some 640 years in the past- and it could be as bright as the full moon. Couple of nitpicks/comments: 1. When Betelgeuse blows, it will be a _supernova_ (i.e. a catastrophic explosion that blows the supergiant star apart). A nova is a much more sedate (in comparison, anyway) phenomenon in which incoming matter (typically from a companion star) repeatedly falls inward to a white dwarf star and ignites on the surface of the star, causing repeated cycles of brightening. Despite the similarity in names, they are two completely different stellar phenomena. 2. While it’s not “wrong” to talk about distant astronomical phenomena as taking place in the past (due to light-speed lag), because there is no faster way for the information to reach us, it’s not particularly relevant either. It’s more relevant for very distant objects (millions or billions of light years distant) because in that case you are literally looking into the distant past earlier in the lifetime of the universe. But for something only about 500 light years away, even that distinction is lost. (The universe likely hasn’t changed much in the last 500 years.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 9, 2026, 1:32am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/229 "2026-09-09T01:32:27Z")
While we’re at it, there’s a popular trope that the light we see is all from stars that are already dead. There are a couple of visible stars for which that might be true, Betelgeuse being one of them, but for almost all stars, it almost certainly isn’t true, and there’s a pretty good chance that none of the stars we see now in the night sky are dead yet. Stars that are individually visible are all fairly close (within around 8000 ly), close enough that if they were fusing then, they’re almost certainly still fusing now. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 9, 2026, 2:50am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/230 "2026-09-09T02:50:15Z")
> [@Chronos](#): > > While we’re at it, Betelgeuse is officially designated “alpha Orionis”, meaning the brightest star in Orion. Or at least, that’s what it meant at the time the names were assigned. It’s been dimmer than Rigel for all of the photometric era. They didn’t always designate the brightest star in the constellation as Alpha. What they did was first designate the first magnitude stars from east to west as Alpha, Beta, etc. Then the second magnitude stars, also from east to west, got the next Greek letters, and so forth until they reached the end of the Greek alphabet. Since most constellation only have a single first magnitude star, that meant that Alpha was the brightest. However, there are exceptions and Orion is one of them. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [September 9, 2026, 3:04am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/231 "2026-09-09T03:04:56Z")
> [@Chronos](#): > > While we’re at it, there’s a popular trope that the light we see is all from stars that are already dead. There are a couple of visible stars for which that might be true, Betelgeuse being one of them, but for almost all stars, it almost certainly isn’t true, and there’s a pretty good chance that none of the stars we see now in the night sky are dead yet. I read there are maybe a couple, one seen only in the Southern hemisphere. But yeah, possible for a couple, but not likely. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 9, 2026, 9:09pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/232 "2026-09-09T21:09:18Z")
> [@dtilque](#): > > They didn’t always designate the brightest star in the constellation as Alpha. What they did was first designate the first magnitude stars from east to west as Alpha, Beta, etc. Then the second magnitude stars, also from east to west, got the next Greek letters, and so forth until they reached the end of the Greek alphabet. Huh, I did not know that. That explains why the stars in Ursa Minor seem to go in order. [Previous page](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478.md?page=11)