# 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:** 3
**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 30, 2019, 4:45am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/41 "2019-12-30T04:45:47Z")
Actually, speaking of that: We can’t say whether Betelgeuse’s recent activity is a sign of imminent supernova, because we’ve never watched a star before it went supernova, and so we don’t have any real idea, beyond unreliable models, what a star that’s about to explode actually looks like. Maybe what we’re seeing from Betelgeuse means it’ll be a few weeks, or maybe it means it’ll be a milennium, and we just don’t know. It’s the same issue with unprecedented geological observations at Yellowstone. We’ve never watched a supervolcano go off, so we don’t know what to look for. ---
**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 30, 2019, 5:20am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/42 "2019-12-30T05:20:23Z")
With respect to the latter, i’m hoping we remain without a real-life example for a long time to come. Let the scientists continue with their models. 😃 ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [December 30, 2019, 5:40am UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/43 "2019-12-30T05:40:37Z")
> [@Chronos](#): > > It’s the same issue with unprecedented geological observations at Yellowstone. We’ve never watched a supervolcano go off, so we don’t know what to look for. > [@Northern\_Piper](#): > > … i’m hoping we remain without a real-life example for a long time to come. Let the scientists continue with their models. 😃 But we need _data!_ ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [December 30, 2019, 12:57pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/44 "2019-12-30T12:57:06Z")
> [@Darren\_Garrison](#): > > Maybe you should have tried that before sticking your foot in your mouth. No foot in the mouth. As I say, Betelgeuse has done this before. People just aren’t aware of its frequent changes in brightness. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 30, 2019, 1:06pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/45 "2019-12-30T13:06:57Z")
> [@CalMeacham](#): > > No foot in the mouth. As I say, Betelgeuse has done this before. People just aren’t aware of its frequent changes in brightness. And you _still_ haven’t read the linked article? I congratulate you on the flexibility of your joints.🙂 Do you imagine that the cited professional astronomers are unaware of the star’s history? ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [December 30, 2019, 1:07pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/46 "2019-12-30T13:07:48Z")
> [@Nansbread1](#): > > The gradual loss of Betelgeuse brightness although not a surprise has been reported as a possible sign that the star may explode. > > If it does indeed destruct and we see the celestial supernova …when did it actually happen? If it goes super nova, it will have happened 642 years ago because it would have taken the light from the explosion 642 years to reach us. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 30, 2019, 1:12pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/47 "2019-12-30T13:12:15Z")
> [@Jasmine](#): > > If it goes super nova, it will have happened 642 years ago because it would have taken the light from the explosion 642 years to reach us. Let us know when the light from the first twenty posts in this thread reaches you, then we can work out how far away you are. ---
**Author:** ![BrotherCadfael](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@BrotherCadfael](https://boards.straightdope.com/u/BrotherCadfael)\ **Post date:** [December 30, 2019, 1:58pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/48 "2019-12-30T13:58:51Z")
_Where’s the kaboom? I was expecting an Earth-shattering kaboom!_ ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [December 30, 2019, 2:31pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/49 "2019-12-30T14:31:03Z")
> [@Chronos](#): > > It would be considerably brighter than the full moon, easily visible during the day, and probably somewhat uncomfortable to look at directly. It would fade over timescales on the order of months. And would it occur virtually instantaneously, i.e. from normal (albeit faded) Betelgeuse to cosmic kablooie in seconds, or would it gradually get brighter over a long period of time? ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [December 30, 2019, 3:00pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/50 "2019-12-30T15:00:21Z")
> [@Colophon](#): > > And would it occur virtually instantaneously, i.e. from normal (albeit faded) Betelgeuse to cosmic kablooie in seconds, or would it gradually get brighter over a long period of time? [Type II supernova light curves](http://astronomy.swin.edu.au/cosmos/T/Type+II+Supernova+Light+Curves) It will not get brighter over a long period of time. Note the rapid rise to peak luminosity over a week or so as the nova expands, followed by a gradual decline. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 30, 2019, 3:26pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/51 "2019-12-30T15:26:13Z")
Some rather astonishing supernova “trivia” (that doesn’t seem like the right word) from xkcd What If: > [@](#): > > Which of the following would be brighter, in terms of the amount of energy delivered to your retina: > > A supernova, seen from as far away as the Sun is from the Earth, or > > The detonation of a hydrogen bomb pressed against your eyeball? Answer halfway down here: [https://what-if.xkcd.com/73/](https://what-if.xkcd.com/73/) ---
**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 30, 2019, 4:26pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/52 "2019-12-30T16:26:26Z")
> [@CalMeacham](#): > > No foot in the mouth. As I say, Betelgeuse has done this before. People just aren’t aware of its frequent changes in brightness. Curious, then, that both of the articles I cited in the MPSIMS thread made exactly that point, to put the current dimming in context: [CBC: Astronomers are wondering whether Orion’s shoulder will soon explode](https://www.cbc.ca/news/technology/betelgeuse-dimming-1.5407038) > [@](#): > > But Betelgeuse is also a variable star, meaning its brightness rises and falls periodically. But we’ve never seen it like this. > > “Maybe 300 years ago, Betelgeuse was dimmer than what we’re observing now, but we don’t have data,” Kafka said. > … > It’s not quite clear why exactly Betelgeuse dims periodically, but one of the possibilities is that, like the sun, it has cooler and hotter parts. If one of those cooler parts swung into our line of sight, that could make it seem like the star had dimmed. > > In 2018, Betelgeuse had a couple of dips in its brightness, Kafka said. What we’re seeing now could be that same spot, or possibly another. [Forbes: Is Betelgeuse About To Explode?](https://www.forbes.com/sites/startswithabang/2019/12/25/is-betelgeuse-about-to-explode/#791690ce47bf) > [@](#): > > Recently, in just the past few weeks, its brightness has dropped tremendously, knocking it out of the top 10 brightest stars for the first time in many years. > … > In fact, if you look beyond the previous decade and instead go back to the past century, you’ll find that Betelgeuse has been this dim many, many times in the past. If you look beyond the photosphere of the star itself, you’ll find that there are enormous radio emissions that reveal the presence of expelled gas out beyond where the orbit of Neptune is around the Sun. > > Similar dimming events have occurred before, reducing the brightness of Betelgeuse below even what it currently is at. But to see a dimming event occur this rapidly and this severely really hasn’t been seen before over the past century at all. It’s almost as if the journalists who wrote these articles were aware of Betegeuse’s pattern of dimming and wanted to inform their readers of that! But naw. “People just aren’t aware of its frequent changes in brightness.” ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [December 30, 2019, 4:35pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/53 "2019-12-30T16:35:05Z")
> [@Riemann](#): > > Let us know when the light from the first twenty posts in this thread reaches you, then we can work out how far away you are. I don’t think you’ve thought this through. ---
**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 30, 2019, 6:44pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/54 "2019-12-30T18:44:51Z")
The variations in Betelgeuse’s brightness are due to multiple factors. One factor is in fact starspots, darker regions of the surface which we believe are due to similar phenomena as sunspots. Another is because its size isn’t constant, but pulsating. Betelgeuse is one of the very few stars with a large enough angular size that it’s possible (albeit still difficult) to resolve it into more than a point source; such observations would be able to tell whether the current dimness is due to pulsation, starspots, or a combination of both. I’m guessing that nobody has had a chance to make such images yet. ---
**Author:** ![pjd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pjd/32/3009_2.png) [@pjd](https://boards.straightdope.com/u/pjd)\ **Post date:** [December 30, 2019, 7:55pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/55 "2019-12-30T19:55:07Z")
> [@Jasmine](#): > > I don’t think you’ve thought this through. 😃 ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [December 30, 2019, 10:07pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/56 "2019-12-30T22:07:14Z")
> [@Mijin](#): > > I didn’t claim that there was. I am just suggesting (or rather, supporting what I think **septimus** was getting at), that there is no absolute time. It is misleading to talk about what time an event “really” happened because all we can ever do is pick a reference frame and say when the event took place in that frame. […] Right! \*\*Chronos \*\*is right in the astronomical convention, what he says is practical. But in a physical way, there is no real time. It is, literally and figuratively, relative. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [December 30, 2019, 10:14pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/57 "2019-12-30T22:14:18Z")
> [@Riemann](#): > > Re frame of reference for the time measurement: > > There is a natural frame of reference when talking about the age of the universe, that’s the time measured on a clock carried by a co-moving observer, i.e. an observer at rest with respect to local space, moving only with the Hubble Flow, with the expansion of space itself. The frame in which you are at rest wrt to local space is the frame in which the universe is isotropic - it looks the same in all directions. […] Are you postulating a \*natural \*universal frame of reference for time and the age of the Universe? And that the coordinate origin of the referece frame is distributed everywhere homogeneously (or where ever the Hubble Flow happens to take you drifting?) If so, I disagree. ---
**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 30, 2019, 10:36pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/58 "2019-12-30T22:36:30Z")
The tricky part with the locally co-moving frame is that it _isn’t_ a frame of reference. It’s a whole bunch of frames of reference, a different one for every point in the Universe. But the locally co-moving frame for Earth is almost exactly the same as the locally co-moving frame for Betelgeuse, both of which are almost exactly the same as the rest frame for Betelgeuse, the rest frame for the Earth, and the rest frame for the Galaxy as a whole. And so, while we could, with perfect validity, use some reference frame that is very different from any of those, there’s no practical reason to. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [December 30, 2019, 11:23pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/59 "2019-12-30T23:23:49Z")
> [@Chronos](#): > > The tricky part with the locally co-moving frame is that it _isn’t_ a frame of reference. It’s a whole bunch of frames of reference, a different one for every point in the Universe. Indeed, but on Earth there is only one frame of reference that makes sense: the local one > [@](#): > > But the locally co-moving frame for Earth is almost exactly the same as the locally co-moving frame for Betelgeuse, both of which are almost exactly the same as the rest frame for Betelgeuse, the rest frame for the Earth, and the rest frame for the Galaxy as a whole. And so, while we could, with perfect validity, use some reference frame that is very different from any of those, there’s no practical reason to. Yes, but they are over 600 Light Years apart, there can not be an event that takes place in one of the two frames of reference that is viewed simultaneously in both frames, they are incompatible. There is no \*now \*here and in Betelgeuze, so there is no \*now \*at all. We use our local frame of reference because there are indeed practical reasons to do so, but this frame is not at all the same as Beltegeuze’s. And it is not absolute. I wonder if we are talking about the same thing, perhaps this is an argument about words? What am I not getting about your argument? I thought we were discussing the possibility that Beltegeuze “has exploded 640 years and one day ago”? That makes no sense: if it was so we will only be able to know it tomorrow, so it did not happen 640 years ago, it will happen tomorrow. Or later. We can not know before the signal arrives, so it has not happened. Do you mean something different by “happened”? ---
**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 30, 2019, 11:47pm UTC](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478/60 "2019-12-30T23:47:40Z")
Our frame of reference is not the same as Betelgeuse’s, but it’s incorrect to say that it’s “not at all the same”. It’s very, very close to being the same. The relative velocity between Betelgeuse and Earth is approximately 34 km/s. That’s 0.0001c, for a gamma factor of 1.000000006. There’s no measurement we can make of Betelgeuse that has anywhere near that level of precision, so for all practical purposes, they’re the same reference frame. [Previous page](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478.md?page=2) [Next page](https://boards.straightdope.com/t/betelgeuse-losing-brightness/845478.md?page=4)