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.
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?
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.
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.”
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.
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.
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.
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.
Indeed, but on Earth there is only one frame of reference that makes sense: the local one
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”?
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.
