That’s only considering the time for light to travel. But there might be other factors:
It might release ultraviolet light before visible during supernovaing.
It might glow purple or some other visible color, too faintly for the naked eye to see, before it’s bright enough to see.
If Hubble was on the wrong side of the earth it would be the last to see it.
Since it is coming from a point source (effectively), it will scintillate in our atmosphere, wildly so when near the horizon, flashing all the colors of the spectrum in the process.
The hubble is only about 150 miles up IIRC. Yeah space is that close. You could drive to space in a half hour if your car went straight up.
Even if it did see it, we wouldn’t know it until after we saw it ourselves. The Hubble communicates with the earth through radio waves.
This has probably come up before, but, relativistically speaking, does it make sense to talk about when something really happened?
Is it even formally correct to say Betelgeuse is 640 light years away, since there are frames where that is not true (obviously it would make sense even so to assume Earth’s frames when describing distances).
One has to be more precise in one’s terminology, but yes, it does make sense to talk about “when something really happened”, and one can define distance unambiguously, though sometimes there are multiple, different unambiguous distances.
YDNRC. Google-fu is better than nofu.
The neutrino emissions would likely be the first observation. For Supernova 1987a, they arrived about three hours before the visible light.. There are a lot more neutrino detectors around now, so hopefully we’d capture more than 24 or so. I’m not sure how well the direction would be known, but if Betelgeuse was already starting to act up, just a rough direction might be good enough to convince astronomers to start observing it in earnest.
You could probably convince astronomers quickly enough, but then the question would be how quickly they could aim their telescopes. There are protocols for what are called “targets of opportunity”, but I don’t know how much lead time those need.
Still, we’d probably get some sort of advance warning (Betelgeuse isn’t exactly a difficult object to study), long enough to set up various contingency plans.
First, the very fact that there are no privileged frames of reference means that we can define frames that correspond to our ‘common sense’ ways of conceiving of things.
A straight line can be defined which passes through the centers of the Sun and of Betelgeuse. The distance between them on that line is 3.84 quadrillion miles (640 LY). Even the several millioin miles which the Sun and Betelgeuse no doubt have moved relative to each other since the 640 LY figure was fixed becomes ‘fuzz’ compared to that distance – an error on the order of 0.0000001%.
Second, what we observe on Earth is Betelgeuse as it was when the light we receive left it back in 1372 AD. We can however describe a locus which makes simultaneity across interstellar distances meaningful: any point on a plane passing through the midpoint of that line at 320 LY away from both the Sun and Betelgeuse, with the other two dimensions of the plane defined as both perpendicular to that line, will be observing light from both systems that has traveled for the same length of time. At that median point, for example, they would see the Sun as it was in 1692 AD, and Betelgeuse as it was in 1692 AD. Other points on that plane will observe both Sun and Betelgeuse at the same moment, earlier than 1692, based on a simple trigonometric equation I don’t want to work in my head.
Absolutely and I said as much. It would be a weird world where every speedo includes “(relative to earth’s frame of reference)”.
My point wasn’t so much about the relative movements of those bodies.
I meant that from some frames of reference, the distance isn’t 640 light years at all. e.g. If I were travelling from the sun to Betelgeuse at 90% the speed of light, the sun and Betelgeuse would appear much closer (I can’t do the maths right now), where “appear closer” is not an illusion but represents their separation in that frame.
Of course, there is something fishy about using a frame that’s travelling between A and B, so I was happy with Chronos’ response.
An interesting concept. Clearly there is a sense of local simultaneity. But in terms of interstellar simultaneity, how do you know whether you are on the midpoint between two bodies (and what, exactly, does midpoint mean, bearing in mind curved spacetime)?
Just quickly skimmed this thread.
Some related questions (Tell me if this has already been covered up-thread):
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What, in fact, will happen to Earth when Beetlejuice goes kablooie? Will we just see another big light in the sky for a while? Will Earth get real hot toasty (but still livable)? Will we all get incinerated?
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If we all get incinerated, how long will the process take? How much time will elapse from when we first observe that the star has gone super-nova, until the time that we start feeling some serious effects? And how much time will elapse from the moment we first being to feel it seriously, until it reaches its worst and we are all charcoal?
Or am I just blowing over-the-top hysteria out my ass here?
[sub]Wait – Did I miss something? Betelgeuse is a moderately distant star in THIS galaxy, right? We’re not talking about looking at one particular star in a totally 'nother distant GALAXY are we? Fight my serious ignorance here.[/sub]
Okay, I just more closely reviewed what has been posted, especially post #3 by Chronos.
[sub]In my fantasy, I was hoping for a little excitement here.[/sub]
Maybe I’m missing something, but if the neutrinos arrived about three hours before the visible light, doesn’t that imply that the speed of light is neither an absolute, or a constant?
Not if they left earlier.
The photons from the Supernova take a while to bounce their way out from the core; Neutrinos can pass through matter without much trouble, so they escape immediately.
Yes Betelgeuse is in this galaxy, visible from Earth as a prominent bright star…other galaxies are many orders of magnitude further away and the few visible to the naked eye (from ideal/dark viewing locations) appear as dim smudges.