Re: Betelgeuse... I was hoping you were gonna show up Bra... I'm glad you did. Well, sure. Anything's possible. But my point was just that it's only massive (and luminous) stars that go supernova and only nearby stars that could have any effect. A nearby, luminous star is going to be pretty damn bright since it fulfills both the criteria for something appearing bright: that it's nearby and putting out a lot of light. That's not going to be missed. V838 is cool because we see light echos lighting up the expanding shells of gas around it. That gives us some idea how big these shells are (since we know the speed of light). The result: they're damn big. This is really interesting because mass loss is one of the primary things that dictates the uncertainty in high-mass stellar evolution. Studying this star will give us ideas of where our models need to be tweaked. The point is the radiation pressure from one of these supernovae is going to be really weak by the time it gets to the solar system. And the shock wave from the SN is never going to reach us. So, while Earth can (and does) get bombarded by high-energy photons, they aren't enough to affect the orbits of Oort cloud objects. Moreover, you need to remember that our solar system is TINY compared to the distance between stars. This means that most of the energy of one of these supernova blast waves is just going to pass on either side of us; it's going to be WAY spread out by the time it gets to us and we're only going to occupy a TINY angle of the expanding sphere. And I'm actually pretty unusual, too. It's more than a guess. It's a physics-based model to try to understand what goes on in stars. We have plenty of examples of supernovae that have been measured (although it's been a while since one has gone off in the Milky Way; we're actually overdue), so we do have some idea of the energy constraints. And we can also compare ensembles of stars to these models and, depending if we've done it correctly, it's either going to match or not. We actually have the stellar evolution models ~95% there. It's just that this final stage of evolution, particularly of high-mass stars, is not totally understood. We've actually made some pretty big leaps in the last 10 years or so. There's no way to know if this star has gone supernova yet. Nothing can travel faster than the speed of light, so we'll only know postfacto if this star went supernova now (or 500 years ago, or whatever). The point is that what we're observing now happened 600 years ago.