# 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:** 20\ **Page:** 9
**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:** [December 10, 2023, 10:15pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/162 "2023-12-10T22:15:29Z")
Telescopes can image Betelgeuse’s disk, but it’s not easy, and I’m not sure they can do it quickly enough to be useful during the transit. In fact, one of the things we’ll be able to get from this transit is much better imaging of the disk of the star. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 12, 2023, 3:06am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/163 "2023-12-12T03:06:48Z")
Well, here in greater Miami I was clouded out. A thin layer of high clouds obscured abut half the sky and was so lit up by city lights that no stars were visible in there clear(er) areas either. Sigh. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 12, 2023, 4:15am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/164 "2023-12-12T04:15:35Z")
Did you try saying Betelgeuse three times? ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [December 12, 2023, 4:50am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/165 "2023-12-12T04:50:55Z")
I just think this is space geek cool personified. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 12, 2023, 1:48pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/166 "2023-12-12T13:48:04Z")
So, has any space geek hunted up any pix, vids, or follow-on articles? The cite upthread and the links directly from it didn’t have much to say. Some folks saw a 6-12 second occultation, but not many. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 12, 2023, 4:45pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/167 "2023-12-12T16:45:32Z")
A report from Italy that the dimming was much less than the 3 magnitudes expected: > **[Betelgeuse's Unexpected Luminosity During Asteroid Occultation](https://ts2.space/en/betelgeuses-unexpected-luminosity-during-asteroid-occultation/#gsc.tab=0)** > > Betelgeuse's Unexpected Luminosity During Asteroid Occultation TS2 SPACE ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [December 12, 2023, 8:19pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/168 "2023-12-12T20:19:35Z")
> [@JohnGalt](#): > > I suppose someone will upload a video to YouTube later. Not great quality but I found [this](https://www.youtube.com/live/4h7qdZwV0_Q?si=g2zybjlWYX9-UbKa&t=8470). ---
**Author:** ![JohnGalt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johngalt/32/184_2.png) [@JohnGalt](https://boards.straightdope.com/u/JohnGalt)\ **Post date:** [December 13, 2023, 3:22am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/169 "2023-12-13T03:22:33Z")
Thanks, it went fast. He said it was partial, so not as impressive as it could have been. I’m glad I didn’t make a special trip to see it. I’d probably get last-minute cloud cover. Here’s hoping for clear weather in April… ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 13, 2023, 3:55am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/170 "2023-12-13T03:55:49Z")
> [@Saint\_Cad](#): > > Added bonus is that telescopes can resolve Betelgeuse’s disk. Today I learnt - something new! I’d always heard that the stars were so far away that they could never be more than points of light. ---
**Author:** ![GIGObuster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gigobuster/32/421_2.png) [@GIGObuster](https://boards.straightdope.com/u/GIGObuster)\ **Post date:** [December 13, 2023, 4:23am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/171 "2023-12-13T04:23:24Z")
Not as disappointed as I was of [Comet Kohoutek](https://www.space.com/comet-kohoutek-flop-of-the-century.html), but still, someone miscalculated. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 13, 2023, 4:57am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/172 "2023-12-13T04:57:08Z")
> [@Northern\_Piper](#): > > I’d always heard that the stars were so far away that they could never be more than points of light. > **[List of stars with resolved images](https://en.wikipedia.org/wiki/List_of_stars_with_resolved_images)** > > The following is a list of stars with resolved images, that is, stars whose images have been resolved beyond a point source.\[clarification needed\] Aside from the Sun, observed from Earth, stars are exceedingly small in apparent size, requiring the use of special high-resolution equipment and techniques to image. For example, Betelgeuse, the first star other than the Sun to be directly imaged, has an angular diameter of only 50 milliarcseconds (mas). ---
**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:** [December 13, 2023, 2:24pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/173 "2023-12-13T14:24:18Z")
For the vast majority of stars, using the vast majority of telescopes, that’s still true. You have to take some seriously extreme measures to get anything but a point source, for those scant two dozen for which it’s even possible: Not just the right telescope, but also the right observational techniques and the right data analysis. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 13, 2023, 4:42pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/174 "2023-12-13T16:42:52Z")
Are the others (that can be resolved) as big as Betelgeuse, or closer? What is it that allows astronomers to see them as discs (with the right equipment you’ve outlined)? ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [December 13, 2023, 7:31pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/175 "2023-12-13T19:31:56Z")
The star with the largest apparent diameter as seen from Earth is R Doradus, with a diameter between .052 and .062 arc seconds. Betelguese is the second largest, at .049 to .060 arc seconds. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [December 13, 2023, 7:55pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/176 "2023-12-13T19:55:16Z")
> [@Northern\_Piper](#): > > What is it that allows astronomers to see them as discs (with the right equipment you’ve outlined)? The fact that they are big fat supergiants with a diameter hundreds of times that of the Sun? ---
**Author:** ![Coriolanus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coriolanus/32/18769_2.png) [@Coriolanus](https://boards.straightdope.com/u/Coriolanus)\ **Post date:** [December 13, 2023, 11:30pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/177 "2023-12-13T23:30:42Z")
I hope some science was gained. Betelguese by being so big and relatively near is a very interesting star. It may be hard to tell the differences in magnitude between blue stars like Rigel which clearly is the brightest start in Oriion (and ought to have been called alpha Orionis) yet some hundreds of years ago Betelguese was apparently the brightest. The blue supergiants like Rigel, the relatively nearby Sirius and the impressive searchlight Deneb are interesting yet they don’t exist long enough as our mediocre Sun and perhaps Betelguese once was. It’s fascinating to me that almost all the heavy elements on Earth came from big blue supergiant supernovas billions of years ago. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 14, 2023, 1:25am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/178 "2023-12-14T01:25:51Z")
> [@DPRK](#): > > The fact that they are big fat supergiants with a diameter hundreds of times that of the Sun? Not all of them are supergiants. The first on the list (after the Sun) is Altair, which is a main sequence A-type star. It’s fairly close (17 ly) which makes it easier to image the disk. Also it’s a very fast rotator, which makes the disk larger albeit non-circular. If Altair’s disk can be imaged, you’d expect Sirius’ disk to also be imageable. After all, Sirius is half the distance, so the disk should be 4 times larger. I expect no one’s tried to image it. Anyway, the next several after Altair are giants, not supergiants. They’re lots bigger than the Sun, but nowhere near as big as a supergiant. For example, when the Sun becomes a giant at the end of its life, it’ll expand to roughly the size of Earth’s orbit. Betelgeuse is over five times that large. ---
**Author:** ![Fish\_Cheer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fish_cheer/32/17179_2.png) [@Fish\_Cheer](https://boards.straightdope.com/u/Fish_Cheer)\ **Post date:** [December 16, 2023, 7:23pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/179 "2023-12-16T19:23:07Z")
That list is very interesting, thank you! What caught my eye, though, was that it gives the distance to Betelgeuse as 643 +/- 146 light years. Is that really the best we can do? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 16, 2023, 7:40pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/180 "2023-12-16T19:40:21Z")
> [@Fish\_Cheer](#): > > it gives the distance to Betelgeuse as 643 +/- 146 light years. Is that really the best we can do? Probably. Traditional parallax distance measurements were only good up to around 300 ly. Anything further than that had really big error bars. Gaia can do a lot better, mostly because it’s outside the atmosphere. From one discussion [here](https://www.cloudynights.com/topic/882142-limits-of-parallax/), its limit should be about 10% error at 4K parsecs (13k ly). However, Gaia has problems measuring parallax for bright stars, especially those with large apparent size such as Betelgeuse. Hipparcos, Gaia’s predecessor, had the same problem. So the distances to those few stars is less well known. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [December 23, 2023, 11:47pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/181 "2023-12-23T23:47:09Z")
The Sun is about a million miles in diameter. Betelgeuse is believed to be about a BILLION miles in diameter. [Previous page](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478.md?page=8) [Next page](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478.md?page=10)