See a Supernova From Your Backyard

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See a Supernova From Your Backyard

Posted by samzenpus on Monday September 5, 2011 @05:00AM from the no-sunglasses-required dept.

hasanabbas1987 writes "Want to catch a glimpse of the closest supernova astronomers have discovered in the last 25 years? All you need to do is get yourself a small telescope or a pair of binoculars (some DSLRs would do just fine as well). Astronomers think that they may have found the supernova within hours of its initial explosion on August 24. Generally, supernovas are around 1 billion light years away but this one is only 21 million light years away. The supernova is in the Pinwheel Galaxy and you can see it within the Big Dipper."

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Discovered within hours of its explosion? by freaktheclown · 2011-09-05 05:07 · Score: 4, Informative

I'm pretty sure it exploded about 21 million years ago.

If a supernova were close enough to be seen within hours of its explosion, we probably wouldn't be here.
1. Re:Discovered within hours of its explosion? by Anonymous Coward · 2011-09-05 05:13 · Score: 1, Insightful
  
  From our reference frame, this happened hours ago. The summary is correct. You are not.
2. Re:Discovered within hours of its explosion? by freaktheclown · 2011-09-05 05:22 · Score: 4, Informative
  
  No the summary is not correct. It did not happen "hours ago" from any reference frame. Other articles written about this got it right; this one did not.
3. Re:Discovered within hours of its explosion? by freaktheclown · 2011-09-05 05:38 · Score: 1
  
  I never made a big deal out of it, but then you insisted I was wrong.
4. Re:Discovered within hours of its explosion? by Iskender · 2011-09-05 05:41 · Score: 2
  
  I suspect that a lot of the time the people pointing it out do so because they have nothing else to contribute to the discussion.
  I'm guessing it's a form of disinterest really - someone sees news about an exceptional supernova and would rather discuss a sentence in a Slashdot summary.
  Some other poster already posted a very constructive post though, I suggest we read that instead: http://science.slashdot.org/comments.pl?sid=2413680&cid=37309370 .
5. Re:Discovered within hours of its explosion? by pyrosine · 2011-09-05 05:45 · Score: 1
  
  You seem to be troubled here: The light from some number of hours after the star going supernova has finally reached us after 21 million years
6. Re:Discovered within hours of its explosion? by exploder · 2011-09-05 05:49 · Score: 2
  
  There's not some cosmic clock that marks a simultaneous "now" for every point in the universe, such that the light from that supernova actually traveled for 21 million years to reach us. Simultaneity doesn't exist, independent of reference frame. In our reference frame, the supernova exploding and the light reaching us are simultaneous events. If you don't believe it, pick up a physics book--even a very watered-down pop physics book from Barnes & Noble will set you straight on this issue.
  
  --
  Yo dawg, I heard you like the Ackermann function, so OH GOD OH GOD OH GOD
7. Re:Discovered within hours of its explosion? by hawkinspeter · 2011-09-05 05:59 · Score: 1
  
  No - it just exploded, but it took 21 million years for it's 'now' to arrive here.
  
  --
  You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
8. Re:Discovered within hours of its explosion? by gmueckl · 2011-09-05 06:11 · Score: 5, Informative
  
  Yet, no time has passed for the traveling light. Or more precisely: if an observer had followed the light emitted from the supernova at almost the speed of light, very little time would have passed in his frame of reference. So what we take as 21 million years would have been nearly instantaneous for our traveling observer. Simultaneity is a weird thing when time is relative.
  
  --
  http://www.moonlight3d.eu/
9. Re:Discovered within hours of its explosion? by interkin3tic · 2011-09-05 06:12 · Score: 4, Funny
  
  Important lesson here: there is no "+1 pedantic" mod. On slashdot or in real life, which is why no one was too interested in making out with you new year's eve 1999 when you were telling everyone that the millennium wouldn't start until the next year.
10. Re:Discovered within hours of its explosion? by Missing.Matter · 2011-09-05 06:17 · Score: 3, Insightful
  
  Because that's what nerds do (and consequently why everyone hates them). They're infuriatingly pedantic, and love to correct people even on the smallest details because it makes them seem smarter (and therefore better).
11. Re:Discovered within hours of its explosion? by fyngyrz · 2011-09-05 06:33 · Score: 4, Insightful
  
  Because that's what nerds do (and consequently why everyone hates them). They're infuriatingly pedantic, and love to correct people even on the smallest details because it makes them seem smarter (and therefore better).
  More accurately presented / corrected is better, and the reason the people you call "nerds" infuriate others is because the lazy and low-functioning hate being reminded the things they believe are imprecise because they don't take the time (or have the ability) to think things out to a more precise conclusion.
  It is not anyone's job to dumb things down (or leave them down, when presented that way) so you'll be comfortable. If the status quo is to be moved, up is clearly the ethical and moral way to move it. If it is not to be moved, you'll need a better reason than "I'm uncomfortable with statements that are more accurate than mine."
  "Getting things right" is a much more laudable human goal than "keeping things approximate."
  Further, in this particular venue, the audience is generally a good deal smarter than, say, on Gawker. If you present in a clumsy or inaccurate manner here, it's really kind of silly to expect it to go unremarked.
  
  --
  I've fallen off your lawn, and I can't get up.
12. Re:Discovered within hours of its explosion? by rubycodez · 2011-09-05 06:36 · Score: 2
  
  Except you pseudo-relativity experts don't understand we can establish our reference frame as a standard, and that the exploding star is essentially in our reference frame, as it is not in relativistic motion in relation to us, nor is it or we in huge potential well in relation to each other. It's just a real-time signal propagation lag we experience, no different than sound of firecracker two city blocks away taking a second to reach you.
13. Re:Discovered within hours of its explosion? by fyngyrz · 2011-09-05 06:39 · Score: 1
  
  Those same physics books have a few things to say about the amount of time that passes at lightspeed, too; as does the light that results from that supernova. Simultaneity is a little difficult to pin down in such cases.
  
  Thought experiment for you: if we pointed a mirror back at the star so they could see their own explosion, according to your logic the light leaving the mirror and reaching the star would be simultaneous events too. So putting A and B together, the light leaving the star, and its mirror reflection returning to the star would be simultaneous events. This would imply instant interstellar communication.
  If you were riding a particle of light in your experiment, that's pretty much what you'd see, yes.
  Unless you're quite specific about your frame of reference here, it is easy to describe the event inaccurately, mismatching the frame with the description.
  
  --
  I've fallen off your lawn, and I can't get up.
14. Re:Discovered within hours of its explosion? by Anonymous Coward · 2011-09-05 07:00 · Score: 1
  
  Last time I checked, history books and news articles report time according to Earth's reference frame. Why do people have to bring in stuff like "If you were riding a particle of light"? If you make that assumption then of course dates are screwed up. Even the US independence is no longer 1776. Please stick to Earth's reference frame, people are already confused enough.
15. Re:Discovered within hours of its explosion? by Missing.Matter · 2011-09-05 07:00 · Score: 2, Interesting
  
  Right, exactly what I was talking about. Sanctimonious, enlarged ego, inflated sense of self importance. This post is a good example why the people I call "nerds" infuriate me and most others. You really believe you're better and smarter than most people don't you?
  
  Further, in this particular venue, the audience is generally a good deal smarter than, say, on Gawker.
  In this particular venue it's especially annoying because we all know about relativity and it's entirely tangent to the discussion.
16. Re:Discovered within hours of its explosion? by SaidinUnleashed · 2011-09-05 07:16 · Score: 1
  
  ^^^This. If only I had mod points...
  
  --
  Shiny. Let's be bad guys.
17. Re:Discovered within hours of its explosion? by Ex-MislTech · 2011-09-05 07:35 · Score: 1
  
  This is one of the major issues of society today.
  The stupid strongly believe they are right.
  The intelligent get modded troll...
  
  --
  google "32 trillion offshore needs IRS attention"
18. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 08:02 · Score: 1
  
  Speaking "it happened millions years ago" is not correct since there's no absolute reference frame.
  In our reference frame it happened days ago.
19. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 08:13 · Score: 1
  
  Yup. And in Earth's frame of reference the explosion happened some days ago.
20. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 08:18 · Score: 3, Informative
  
  It IS different. With a firecracker we have a flash which reaches us 'instantaneously' and then a sound which takes a few moments to reach us. Moreover, different observers with clocks synchronized to a same source would see the flash at the same time (we're ignoring relativity) so they can agree on a universal frame of reference (Earth + UTC time).
  With light it's different. We have NO other faster channel. Imagine that you have no way of knowing that firecracker has exploded except by listening to a sonic boom. And you have no faster way to communicate except by shouting.
21. Re:Discovered within hours of its explosion? by MokuMokuRyoushi · 2011-09-05 08:22 · Score: 1
  
  You're mixing time and point of view(or more accurately, time and light's travel time).
  
  you could travel to Procyon (11.4LY away) and watch Shrub take the oath of office on the White House lawn. For us, it happened 11 years ago. For Procyon, it's about to happen.
  11 years ago, it happened. Period. It happened here and it happened in Procyon. The fact that Procyon doesn't see it happen til 11 years later doesn't mean it didn't happen 11 years ago, it simply means that Procyon is 11 light years away and can't know it happened until the point that they see it. You see?
  
  --
  Humans are terrible replicators of Godly things.
22. Re:Discovered within hours of its explosion? by dmartin · 2011-09-05 08:35 · Score: 1
  
  Except we don't.
  Many of the discussions are saying that an object 21 million years ago had to have blown up that long ago. There are even discussions of "there is no reference frame for time", suggesting that they are just using Galiean relativity. There are many other discussions pointing out incorrectly that in Earth's frame it was discovered within hours. The reason this is incorrect is that (to a good approximation) the star and Earth are not in relative motion, they are just separated by a considerable distance.
  There have just been a couple of people pointing out the correct statement in terms of reference frames, namely that someone traveling at nearly the speed of light and following the beam would have experienced relatively little time. There are others that point out the statement actually means we detected the supernova within hours of the first rays of light reaching us.
  I think the real reason people get infuriated with "nerds" is that they spend so much time insisting that they are right, being pedantic about the details while still harboring many misconceptions -- then getting defensive when these misconceptions are bought to their attention.
23. Re:Discovered within hours of its explosion? by superdave80 · 2011-09-05 09:15 · Score: 2
  
  Let's do a simple example to show you why you are completely wrong.
  Let's say your grandma dies right in front of me at 12:00 noon. I call you, and leave a message saying what happened. You don't check that message until 6:00 p.m. Are you really going to try and convince people that grandma died at 6:00 p.m.? Of course not.
24. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 09:21 · Score: 1
  
  "You can prove that easily enough by taking a single inertial frame of reference, extending it out arbitrarily long, and watching the light speed delay"
  Except you can't do this. There's such a thing called 'light cone' and events outside of our light cone are NOT well-defined from physical point of view. And if you try to define it naively by extrapolating observer's future path - you're going to be in a world of hurt because galaxies move relative to each other and the space itself expands.
  For example, imagine an observer on Earth ten weeks ago watching the star that is going to become supernova. It is going to become a supernova a few weeks later, but there's no way to know this.
  Another example, when I speak "I was born in 30 years ago" that means I can get my diary from ten years old which say that I was 20 years old at that time. Not so with the supernova - it has not HAPPENED few weeks ago here.
25. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 09:26 · Score: 1
  
  Nope, you've failed your community college.
  Read about light cone. Assume that the point of the light cone is 1 week ago (at the time when explosion has been registered). What is the time difference between explosion and the apex of that light cone? Answer: zero, since light travels at time-like paths.
  That's the _natural_ way of defining time distances in relativity.
26. Re:Discovered within hours of its explosion? by Raenex · 2011-09-05 10:34 · Score: 3, Informative
  
  It did not happen "hours ago" from any reference frame.
  Is that really true? Somebody mentioned elsewhere in this thread that:
  "Yet, no time has passed for the traveling light. Or more precisely: if an observer had followed the light emitted from the supernova at almost the speed of light, very little time would have passed in his frame of reference. So what we take as 21 million years would have been nearly instantaneous for our traveling observer."
  It seems that you can define a reference frame arbitrarily close to the speed of light at an arbitrary starting position and get the desired duration.
27. Re:Discovered within hours of its explosion? by dmartin · 2011-09-05 10:39 · Score: 1
  
  And by the way, if you think I'm being pedantic, I'm not. I'm objecting to your implication that anyone who didn't make that specific useless statement obviously doesn't understand relativity.
  That is not the statement that I am making. The statement that I am making is that of the people that make statements about reference frames, the majority are incorrect, particularly those that make the statement that it has only been a couple of hours in the Earth's frame.
  I am ambivalent about people who took the statement at the intended reading "discovered within hours of the first light rays arriving at Earth" as they have not demonstrated a lack of knowledge about relativity.
28. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-05 11:08 · Score: 2
  
  This is correct. From the Earth's reference frame, this supernova just occurred, and it occurred 21M LY away. As I demonstrate with an example below, it is misleading and meaningless to talk about how long ago it occurred, or in which order things occurred using any other frame of reference.
  Suppose a supernova 1000LY away had two stars near enough that the supernova had an effect on them, and one of those stars (star B) was 5 LY from the supernova and one (star C) was 15 yr from the supernova. However, star C is 990 LY from earth, while star B is 1005 LY from earth. The high energy rays from the supernova will have an effect on star C 15 years after the supernova, and we'll observe that effect 990 years afterward for a total 1005 years after the supernova. Star B will be effected 5 yrs after the supernova, and we'll observe it 1005 years after that, or 1010 years after the supernova. So, 1010 years after the supernova, we will have seen all three events reach earth, but not in the order in which they occurred relative to the supernova. We observe the effect on star C 5 years before we observe the effect on star B, even though star B was 10 LY closer to the supernova and "happened first" or "longer ago".
  Now suppose (purely hypothetically, since we don't know that it's even possible) that stars B & C both emit deadly gamma ray bursts directed at earth as a result of the supernova. The burst from star C would reach us 5 years after we observe the supernova, and 5 years before we even observe the effect on star B. We would be dead and never see the effect on star B. It doesn't matter that B also emitted a deadly burst, or that "it happened first". What matters is the order in which they effect the destination, and as this example shows, that doesn't depend upon what order they occurred in from another reference frame (e.g. the frame of the supernova), or "how long ago" they happened. The effect on star B clearly happened "10 years before" star C, but what had an effect on earth first was star C, therefore making the effect on star B irrelevant to earth's frame of reference. While it's accurate that from earth's reference 10 yrs after we observe the supernova that the effects on star B happened 1005 years ago while star C was 995 yrs ago, it's also misleading and meaningless because the "more recent" event is the one that first caused a problem on earth. Causality is only relevant at the destination frame of reference, and everything occurs when it is observed, not "xx years ago".
  The physical universe is called space-time for a reason, you can not refer to space and time independently except from a single reference frame. Causality in relativistic frames (and all frames in space-time are relativistic, even if you're not moving at relativistic speeds), requires that all events be sequenced by the frame of the observer, otherwise you will encounter paradoxes of causality where some observers in different reference frames (different places in space-time) will observe two effects a and b in the opposite order. Each is correct from the frame of reference, yet it's inconsistent to say that a occurred before b, or that b occurred before a, and it's misleading to say that a occurred x years ago and b occurred y years ago because the effects on the observer are based upon their arrival at the observer's frame of reference, not the order in which they occurred in any other reference frame.
  
  --
  make imaginary.friends COUNT=100 VISIBLE=false
29. Re:Discovered within hours of its explosion? by Kagura · 2011-09-05 11:48 · Score: 5, Interesting
  
  TO READERS OF THIS STORY'S COMMENTS: If you want to read the real comments for this story, scroll 3/4 of the way down the page to skip that ridiculous "when is now in relativity" arguing that shows up in EVERY cosmology story on Slashdot. Seriously guys, shut up already.
30. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 12:51 · Score: 1
  
  "Yes, and you don't understand what a light cone means, obviously. Events outside of our light cone are not yet causally linked"
  That's why the expression "it happened 21 millions years ago" is not well-defined. Because it has NOT happened 21 million years ago here.
31. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 12:55 · Score: 1
  
  You cannot establish 'true' simultaneity, you can just agree to make one observer 'privileged' and use their order of events.
32. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 12:59 · Score: 1
  
  Additional problem is, that this event has actually not happened 21 million years ago even if we gloss over ill-defined nature of objects outside of our light cone.
  Earth is not stationary with respect to the Pinwheel Galaxy, so the interval will contain space-like component. And then there's the matter of General Relativity and space inflation. Both are not insignificant at these scales.
33. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-05 13:31 · Score: 1
  
  No, it exploded when the light reached us, and we're watching it expand now. Lightning strikes when we see the flash, the shockwave we call thunder lags behind the light, your analogy is flawed. See my post above for a detailed example of why it's inappropriate to say it happened 21M yrs ago.
  
  --
  make imaginary.friends COUNT=100 VISIBLE=false
34. Re:Discovered within hours of its explosion? by lennier · 2011-09-05 14:06 · Score: 1
  
  Yet, no time has passed for the traveling light.
  
  So how come something happens to the photon rather than nothing? How come the emission of that photon from the supernova comes "before" its absorption in the CCD detector in our telescope? There's no time for anything to happen to it, it's travelling infinitely fast in a zero-dimensional world according to the Lorentz contraction, so why should it even interact with the rest of the universe at all?
  
  --
  You are not a brain: http://books.google.com/books?id=2oV61CeDx-YC
35. Re:Discovered within hours of its explosion? by lennier · 2011-09-05 14:16 · Score: 2
  
  With light it's different. We have NO other faster channel.
  Are we so sure we don't? Or did we just decide that since we hadn't measured any such channel in 1905, then there isn't?
  It seems to me that Einstein arbitrarily decided to assume that there exists no faster channel than light in order to redefine the Lorentz contraction as a spacetime effect. Which was a clever hack and made the maths simple, but isn't much of an explanation because it then leaves us with not only no answer to "so what is the physical mechanism which causes space and time between events to appear to dilate as relative motion approaches C", but also makes it impossible to find an answer because it disallows asking the question - it shoves "why" under the carpet of kinematics, not dynamics. And assuming C is the maximum speed of signal propagation causes no end of trouble when you attempt to reconcile relativity with quantum mechanics.
  
  --
  You are not a brain: http://books.google.com/books?id=2oV61CeDx-YC
36. Re:Discovered within hours of its explosion? by lennier · 2011-09-05 14:24 · Score: 1
  
  events outside of our light cone are NOT well-defined from physical point of view.
  That's a correct description of our current physical models, yes. But I'm not sure that non-well-definedness in our physical models is a thing we should be celebrating as a great achievement. In mathematics, that usually means we've done something wrong. And the universe seems to exist just fine whether or not we model it, so perhaps our models aren't 100% complete?
  
  --
  You are not a brain: http://books.google.com/books?id=2oV61CeDx-YC
37. Re:Discovered within hours of its explosion? by quenda · 2011-09-05 15:02 · Score: 1
  
  In our reference frame it happened days ago.
  Only if your reference frame includes infinite light speed. I'd like to see your maths for that one.
38. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-05 16:52 · Score: 2
  
  You think wrong, I didn't lose or disprove my argument. Go back and re-read my entire post.
  For Earth, it happened a week ago. Only from the space-time of the supernova did it actually happen 21M years ago, and we're not in that space-time. From ANY other reference, it DIDN'T happen 21M years ago, it happened less than that, or (for distances greater than 21M LY) it hasn't even happened yet. That's why it's misleading and meaningless to say it happened 21M years ago. It happened last week, and it is/was 21M LY distant in space-time.
  We can calculate that in it's frame of reference it happened 21M years ago, but that frame of reference is meaningless to anyone/thing who wasn't in that space-time. Saying it happened 21M years ago for us requires a concept of a universal simultaneity (universal "now"), which would require that information be transmitted across space-time instantly, vastly exceeding the speed of light, which as far as we can tell, isn't possible.
  
  --
  make imaginary.friends COUNT=100 VISIBLE=false
39. Re:Discovered within hours of its explosion? by wdef · 2011-09-05 17:03 · Score: 1
  
  I'd hazard a guess and say:
  From the photon's "point of view", nothing does happen to it en route. Actually there is no "en route". It's the universe that's abruptly crazy at the boundary conditions at each end.
  Also, special relativity per se doesn't know what a photon is: SR is closely related to Maxwell's equations and so thinks in waves rather than quanta, if you will. The process of a photon being emitted or absorbed is a quantum mechanical event. SR and QM have never been fully integrated into one theory and so a unified description would be required to model what you are describing?
  Also, I'm not sure that "from the photon's POV" can have any physical meaning outside a thought experiment but it does sound doubtful.
40. Re:Discovered within hours of its explosion? by wdef · 2011-09-05 17:13 · Score: 1
  
  With light it's different. We have NO other faster channel.
  Are we so sure we don't? Or did we just decide that since we hadn't measured any such channel in 1905, then there isn't?
  It seems to me that Einstein arbitrarily decided to assume that there exists no faster channel than light in order to redefine the Lorentz contraction as a spacetime effect. Which was a clever hack and made the maths simple, but isn't much of an explanation because it then leaves us with not only no answer to "so what is the physical mechanism which causes space and time between events to appear to dilate as relative motion approaches C", but also makes it impossible to find an answer because it disallows asking the question - it shoves "why" under the carpet of kinematics, not dynamics. And assuming C is the maximum speed of signal propagation causes no end of trouble when you attempt to reconcile relativity with quantum mechanics.
  But we have no evidence that there is any faster channel. And the Lorentz contraction and time dilation aren't merely an illusion; these have been proven to be real.
41. Re:Discovered within hours of its explosion? by dominious · 2011-09-05 20:33 · Score: 1
  
  I just hope someone thought to post the obligatory spaceballs quote somewhere in the thread ...
  Just look at the comments in this dupe story that got in the front page not long ago:
  http://science.slashdot.org/story/11/08/26/1236202/Instant-Cosmic-Classic-Supernova-Discovered
  
  Also, you must be new here.
42. Re:Discovered within hours of its explosion? by sFurbo · 2011-09-05 20:51 · Score: 1
  
  Are we so sure we don't? Or did we just decide that since we hadn't measured any such channel in 1905, then there isn't?
  Basically, from the set {faster than light communication, relativity, causality}, you can pick two. Relativity has done remarkably well in predicting what we would observe, and continues to do so. Causality seems to hold up, so the natural assumption is that no communication faster than light is possible. But it could be wrong, we could live in a non-causal universe, or the true theory behind relativity could be compatible with both.
  
  isn't much of an explanation because it then leaves us with not only no answer to "so what is the physical mechanism which causes space and time between events to appear to dilate as relative motion approaches C", but also makes it impossible to find an answer because it disallows asking the question - it shoves "why" under the carpet of kinematics, not dynamics.
  Isn't that what any physical hypothesis does? Explain some observation to a certain degree? You can always ask "but how?", even if a further hypothesis was made.
  
  And assuming C is the maximum speed of signal propagation causes no end of trouble when you attempt to reconcile relativity with quantum mechanics.
  It does? How? I always thought the problem was elsewhere, in quantification of space and time, which, when combined with the uncertainty principle, gives nonsensical result for any model made so far.
43. Re:Discovered within hours of its explosion? by Rakshasa-sensei · 2011-09-05 21:40 · Score: 1
  
  How can you be so sure? Nothing travels faster than the speed of light and time stands still for the photons so no time has passed between the moment they were emitted and when they were observed by us.
44. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 22:33 · Score: 1
  
  Just admit that you have no clue, ok?
  I'm not claiming that events happen when light cones intersect. I'm claiming that coordinates for events outside of our light cone are ill-defined. Because it requires to extrapolate position of observer into future to define them correctly.
45. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-05 22:50 · Score: 1
  
  Sure, that's what I mean by making one observer privileged. You pick his frame of reference and extrapolate what happens in it from another reference frames.
  But note this: you can not KNOW what happens in another reference frame until the signal reaches you. For instance, suppose that there are two observers and a firecracker in the middle between them. When the firecracker explodes, observer A can predict that according to his previous information observer B should see the firecracker in 1 second and observer B's reaction to the explosion should arrive to observer A in 3 seconds.
  However, observer A has no way to _know_ what is going to happen (unless they have the full knowledge of the universe and can accurately predict everything). There's no way to be sure that observer B has not been wiped out by a passing black hole just before the firecracker exploded.
46. Re:Discovered within hours of its explosion? by miffo.swe · 2011-09-05 23:45 · Score: 1
  
  Its only weird for people with a very bad grasp of reality. We KNOW the speed of light but you want us to ignore that fact and pretend we dont know it. At the same time we are supposed to take other things into account that are not yet proven, but mere indicators of a possibiltiy that time advances slower at light speed for the truth?
  
  --
  HTTP/1.1 400
47. Re:Discovered within hours of its explosion? by thasmudyan · 2011-09-05 23:51 · Score: 1
  
  Our reference frame does not magically cause a photon to travel 21 million LY in zero time, so this did not happen hours ago for anybody. Just because information travels at the speed of light doesn't mean events don't happen before we see them. By your line of reasoning, the Big Bang just happened because photons from around that time are still hitting our detectors today.
  It's amazing how many people get this stuff wrong. I blame physicists who make it a habit to formulate anything related to relativistic effects (or quantum physics for that matter) as misleadingly as humanly possible.
48. Re:Discovered within hours of its explosion? by Lumpy · 2011-09-06 00:34 · Score: 1
  
  Both are correct.
  
  --
  Do not look at laser with remaining good eye.
49. Re:Discovered within hours of its explosion? by delt0r · 2011-09-06 00:57 · Score: 1
  
  Time travels slower in a fast moving reference frame relative to a slower moving reference frame. This has been proven many many times. In fact every time you use GPS. The GPS satellites are traveling quite fast relative to us. Without a proper time dilation correction, GPS fixes would drift km per month. There are many more examples, including having 2 atomic clocks, one on earth one on the spaceshuttle. Decay of particles (muons would not make it to sea level without time dilation), so on and so forth.
  
  GR and SP have been pretty thoroughly tested.
  
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50. Re:Discovered within hours of its explosion? by delt0r · 2011-09-06 01:02 · Score: 1
  
  Do some GR and then tell me the math is simple. The speed of light thing being a constant was something from Maxwell equations and *experimental* evidence. Add the postulate that the laws of physics are the same in every inertial frame of reference you get SR. Add acceleration, you more or less get GR (kinda).
  
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51. Re:Discovered within hours of its explosion? by SlippyToad · 2011-09-06 01:11 · Score: 1
  
  Are we so sure we don't? Or did we just decide that since we hadn't measured any such channel in 1905, then there isn't?
  Yes, because in the 106 years since Einstein's breakthrough, nobody has done any more physics. Jesus.
  
  It seems to me that Einstein arbitrarily decided to assume that there exists no faster channel than light in order to redefine the Lorentz contraction as a spacetime effect
  You seem very smart. Why don't you write us a book on physics and set all our sorry asses straight?
  
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52. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-06 01:24 · Score: 1
  
  Cite some problem with my post. Posting as AC giving a blanket assertion that "there are so many problems with your post" without citing any examples or any referencing any information to back up your assertions indicates that you have no idea what you're talking about.
  
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53. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-06 02:10 · Score: 1
  
  Saying something is/was/occurred 21M LY away does not require "absolute time". 21M LY is a measure of space-time. Space and time aren't separate, that's fundamental to understanding relativity, and that's why we now use the term space-time. A LY is a measure of distance in space-time, not a measure of time.
  Because the speed of light is a limit for how fast information or matter can travel, the very concept of simultaneity at two different points in space-time is a flawed concept. Simultaneity or "universal time" would require that information can be transmitted instantaneously across space-time, which violates all we know about physics. Both information transfer, and causal effects are limited by the speed of light, therefore, something occurs in space-time, "when the first light" from that event reaches (or could reach) a given point in space-time, and not before.
  Here's an extreme example. Suppose that a cataclysmic event occurred 1B LY away from Earth, and that event destroys the universe, however, since it can't move faster than the speed of light it will take 1B LY to reach Earth. Now let's suppose that the event will reach earth 600M years from now. Given that it's 1B LY away, we can calculate that "it happened" 1B-600M = 400M years ago (in the space-time where the event happened). However, as a resident of Earth, you wouldn't say the universe ended 400M years ago, that would be misleading and meaningless, as clearly the Earth is still here, and (in this example) would be for another 600M years. There is another problem with even making that calculation, and that is that unless information can be transmitted faster than the speed of light, we couldn't know about it until it reached Earth 600M years from now, at which point Earth wouldn't exist so it would be meaningless to say that a cataclysmic event that destroyed the the universe happened 1B years ago, it happens when it reaches Earth. Either way, it's meaningless and misleading to say it happened XX years in the past.
  
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54. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-06 02:51 · Score: 1
  
  If it occurred 21M years ago for Earth, then you should be able to study it's history and impact on earth for the last 21M years. You can't, it didn't happen for Earth until a week ago. Saying it happened 21M years ago is a calculation based upon its estimated distance from Earth and the fact that we observed it last week. For Earth, it happened a week ago, and it's 21M LY distant in space-time. Any other interpretation is purely artificial and based upon it's calculated distance from us.
  Let's take an extreme example. Assume (hypothetically) that the explosion destroyed all animal life on Earth. When would animal life on earth die? Not 21M years ago, it would have happened last week. It would be meaningless and misleading to say that it happened 21M years ago, as we were all here 2 weeks ago.
  Talking about when events in space-time occurred from any reference point other than the one you're in is meaningless and misleading. Space and time aren't two separate things, they exist together as space-time. Events happen at an observer's reference only when there has been sufficient time for light to travel between the origin and observation points in space-time. At least, that's what our best theories of physics indicate.
  
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55. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-06 03:17 · Score: 1
  
  Not causally linked means that in the region of space-time that isn't yet causally linked it hasn't yet happened. It didn't happen in our part of space-time until last week. For Earth, the supernova happened a week ago, at an estimated space-time distance of 21M LY. If it happened more than a week ago for us, show me it's any of it's history from some time before we first detected it. Obviously, that's not possible. It didn't happen for us until last week.
  The only frame of reference in which it happened 21M years ago is the frame of the progenitor star. Everywhere else in space-time, it happened less than 21M years ago, and for regions of space-time more than 21M LY from the supernova, it hasn't even happened yet.
  
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56. Re:Discovered within hours of its explosion? by ah.clem · 2011-09-06 04:08 · Score: 1
  
  The stupid strongly believe they are right.
  The intelligent get modded troll...
  About 9% of the population have an IQ above 120. The "stupid" have felt empowered in the last 30 years or so; they used to keep their opinions to themselves but a combination of right wing media (who know exactly how to manipulate the ignorant) and e-mail/Internet (a gathering place for the LCD) as well as other factors has fostered the belief that because there are a lot of "Me too's" out there, it makes them right. Mob mentality at it's finest; burn the witch. I refer you to Cyril M. Kornbluth's "The Marching Morons" published in 1951 for a humorous lampoon of this phenomenon. Obviously, there are other factors, such as easier available credit to the masses, the mistaken belief that the acquisition of material goods equals class equality and/or intelligence, etc. Just my observation and opinion.
  
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57. Re:Discovered within hours of its explosion? by hawkinspeter · 2011-09-06 04:30 · Score: 1
  
  Hear hear!
  
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58. Re:Discovered within hours of its explosion? by Cyberax · 2011-09-06 05:25 · Score: 1
  
  Yes.
  My weather channel can give predictions with certain level of probability. It can not predict the future with 100% probability or see 21 million years into the past.
59. Re:Discovered within hours of its explosion? by gstrickler · 2011-09-06 06:38 · Score: 1
  
  If you bothered to read any of my other posts, or if you actually understood causality and space-time intervals you would know "The paths of particles and light beams in spacetime are represented by time-like and null (light-like) geodesics (respectively)". And null (light-like) intervals are always 0. Therefore, the supernova actually happened on earth when the light-cone reached Earth, or approximately 1 week ago. That it was 21M LY distant in space affects the magnitude of it's impact on Earth, however, it didn't happen 21M years ago in our frame of reference, it happened last week on earth. It was only 21M years ago in the frame of reference at the origin 21M LY away (and wasn't 21M years ago at any other place in the universe)
  Here are some other links you might want to study relativity of simultaneity, absolute simultaneity, space-time, special relativity, and general relativity
  
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60. Re:Discovered within hours of its explosion? by SiChemist · 2011-09-06 06:44 · Score: 1
  
  Ahh, but did the explosion even happen until someone OBSERVED those particles/waves emitted by the explosion?
  (Before the inevitable flames, I AM JOKING, I'm not an idiot. Well, I'm definitely joking anyway.)
  
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61. Re:Discovered within hours of its explosion? by miffo.swe · 2011-09-06 18:02 · Score: 1
  
  This has not been proven, just correlated. The speed of light has been proven but time dilation still waits for proper experiments to prove it. I try not to have faith in things, but thats probably why im not religious either.
  
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62. Re:Discovered within hours of its explosion? by Ofloo · 2011-09-06 18:36 · Score: 1
  
  does it even matter when it happend? time is relative, light moves faster then the radiation just because it moves at the speed of light and is also less old so i think it's going to be hard to determine an age, but anyways, all this is about is that you'll be able to spot a supernova, which is like one in a life time thing.
63. Re:Discovered within hours of its explosion? by delt0r · 2011-09-07 00:08 · Score: 1
  
  And what would constitute proof for you? People on the space shuttle *measured* time dilation. The atomic clocks in the GPS satellites directly measure it every day. It has been directly observed and measured many many times. If that is not proof, nothing will be, and you subscribe faith to things that require none.
  
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64. Re:Discovered within hours of its explosion? by dmartin · 2011-09-07 06:01 · Score: 1
  
  I didn't make the unqualified statement that only that particular frame was the correct one. My qualified statement was that this was the correct statement in terms of reference frames. That is, if you wanted to use relativity to make the statement in the article correct this is how you would do it.
  Since one of the two statements I am making is that the majority of people who are making comments about relativity don't understand it, the "particularly" refers to people thinking that picking a different origin significantly alters the time taken [for these purposes the relatively small GR effect of the Earth's gravitational well makes near no difference]. For the people who say that it has been around 21 million years (implicitly assuming a frame that is comoving with the Earth) are indeed correct, but unless they were mentioning relativity somewhere else in their post they have given no evidence that they do or do not understand how time dilation works.
Supernova fun! by Mr.+Underbridge · 2011-09-05 05:10 · Score: 5, Informative

Just as a warning to those trying star-hunting for the first time: finding this guy can be tricky. Best thing is to get some charts from AAVSO.org. Use 2011fe as the search. Print a 15 degree chart for finding the general area from the big dipper, then 1 degree and 2 degree charts for finding the supernova.
For now, the supernova is getting easier to find by the day - I tried last week and couldn't find it, but now it's pretty bright. However, finding the correct area can be tough because there's no obvious landmarks in the area unless your sky is dark enough to make out the face of the galaxy. And, unless you live in an exurban or rural area, it won't be. Otherwise, you'll need to rely on patterns of stars at the 1 degree scale. Otherwise, you can easily be looking at the supernova but not know which star it is.
There are good threads over at cloudynights.com that provide helpful images and advice. Good luck all! It's really fun to know that you're looking at something that didn't exist last month (correcting for travel time of the light, of course).
1. Re:Supernova fun! by hedwards · 2011-09-05 05:43 · Score: 1
  
  Google has an App for that, oh wait, you want to actually see it, never mind.
2. Re:Supernova fun! by ArsenneLupin · 2011-09-05 07:17 · Score: 1
  
  Search for 2011fe take you to a page in spanish...gee..thanks a lot.
  Indeed, thanks alot. Someone really should explain to those damn spaniards the difference between a supernova and the moon! So, how do I now get that horrible image wiped off my retina?
Re:ha, triangles by Dunbal · 2011-09-05 05:17 · Score: 2

Also chicks dig geometry. I get lots and lots of chicks... I think.
I think that has a lot more to do with you pouring bread-crumbs all over yourself than geometry.

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Huge Optics Needed by Iskender · 2011-09-05 05:32 · Score: 5, Informative

Another warning from another astronomy enthusiast: note that the guy in the video talks about "decent-sized" binoculars and then specifies 20x80 or 20x100.
That 100 at the end means the lenses at the front have a diameter of ten centimetres (four inches) each! So under any normal circumstances those are considered HUGE rather than decent binoculars.
My advice on how to see this supernova: ask someone into astronomy who has a telescope or huge binoculars. Doing the observing "from scratch" is probably a too tall order.
1. Re:Huge Optics Needed by hedwards · 2011-09-05 05:55 · Score: 1
  
  I was wondering about that, because even with my 200mm lens with a 1.6x crop factor trying to take a photo of the moon is really tough to do, as it's far enough away that metering doesn't really work very well.
  This event is happening significantly further away, which makes me wonder what sort of a lens one would need in order to observe it. I'm guessing that you'd need something on the order of a 1000mm lens to get a halfway decent view. At 500mm you're getting a 5 degree view, and I'm guessing that you'd need to get closer than that. And even that's probably underestimating things.
2. Re:Huge Optics Needed by Iskender · 2011-09-05 06:11 · Score: 4, Informative
  
  1.6x crop probably means you have a Canon DSLR. All I can say is that you should really explore the manual modes - with digital you can just try different shutter speeds until you get it right. The moon is illuminated by the sun so the settings that work in sunny daylight should work for photographing the moon too.
  Photographing stars often isn't a matter of magnification, but rather of light gathering. Only few stars are close/large enough to be imaged as disks, and that's with professional equipment - you'll never resolve a star into a disk yourself.
  Rather, stars are point sources. Everything comes from a single point, only the intensity and colour of that point varies. If you want to see fainter stars with a camera, you just need to expose longer. An 18-55 kit lens might very well be able to image this given the right other circumstances. The resolution of 500 mm would be more than enough in any case.
  In fact, the hardest problem would probably be to get low enough magnification - the sky moves all the time and therefore everything is blurred when you make the shutter speeds longer. This means you need large apertures more than you need long focal lengths, and pretty fast you need a tripod/mount that's capable of tracking the sky.
3. Re:Huge Optics Needed by ceoyoyo · 2011-09-05 07:55 · Score: 2
  
  The focal length of the lens and the distance of the object has very little to do with it.
  You can't get a good picture of the moon in an automatic mode because it's very bright. Go to a manual mode, dial in 1/250 s (to start) at f8 and move around until you get a picture you like.
  Focal length isn't going to make a bit of difference when you're looking at something 21 million light years away. It's a point, no matter what. The focal length of your lens will determine whether you JUST get a point of light in the frame, or whether you get some surrounding stars for context.
  No matter what, your light meter is completely useless when taking pictures of stars.
4. Re:Huge Optics Needed by hedwards · 2011-09-05 09:35 · Score: 1
  
  If focal length isn't going to make a difference, then why did the astronomers recommend using binoculars that are giving that much magnification?
  And yes, it's going to be worthless for taking photos of stars, but by the same token, if you need that much magnification to see the super nova, then I'm not sure why a camera would be any different.
5. Re:Huge Optics Needed by ceoyoyo · 2011-09-05 10:41 · Score: 1
  
  They recommend 20x100 binoculars. The 20 is the magnification. The 100 means 100 mm, which is the "aperture," or light gathering capability of the binoculars. I put that in quotes because I mean actual aperture, not the aperture/focal length ratio photographers usually mean when they say "aperture." Think of it (roughly) as the diameter of the main lens. The supernova is dim, so you need a fair amount of light gathering power to brighten it to where you can see it with your eyes. If you're using a camera you can make up for a smaller aperture with a longer exposure.
  Magnification is completely irrelevant when you're looking at a point source like a star or a supernova, except that it determines your field of view, which makes a more or less pretty picture. But a point is still a point no matter how much you magnify it.
6. Re:Huge Optics Needed by GumphMaster · 2011-09-05 10:45 · Score: 2
  
  They recommended 20x80 or 25x100 binoculars. The second number is the diameter in mm of the objective (front) lens. It needs to be this big in order to collect sufficient light to make the object clearly visible to a naked eye. The first number is the magnification (crudely speaking the ratio of objective to eyepiece focal lengths). 20 is simply the common magnification in binoculars, which have fixed eyepieces, with objective lens sizes large enough to be useful.
  You'll also notice that when recommending a telescope there's no mention of focal length or magnification at all, just object lens/mirror size > 75mm. Eyepieces in telescopes can be changed to change magnification and field of view but it is the collecting area that is truly important to making the dim visible.
  Now, if only someone could move M101 about 10 or 15 degrees further south I might have a hope of seeing it.
  
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7. Re:Huge Optics Needed by gstrickler · 2011-09-05 12:55 · Score: 4, Funny
  
  All requests for moving galaxies or altering the axis of the earth must have been made (in triplicate) more than 1B years ago. Request denied.
  
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8. Re:Huge Optics Needed by BlackPignouf · 2011-09-05 20:55 · Score: 1
  
  It's possible to take decent moon pictures with any camera.
  320mm equivalent is more than enough to get some serious details (craters and stuf..).
  your problem is probably some serious over-exposure, where the moon is a completely motion-blurred washed-out white disc.
  Get to Manual mode, choose f/8, 1/400s, ISO 800 and see what you get. The auto focus might have problems, so just focus close to infinity and adjust it with magnified live-view (if available).
  It works best when the moon is half lit, so that the surface's texture is shown by the low directional light.
  Motion blur, over-exposure or under-exposure are all easily manageable by playing with shutter-speed, aperture and sensitivity. If you don't know what they are and what they do, let google help you.
  Have fun!
Re:Gamma rays? by TheRaven64 · 2011-09-05 05:43 · Score: 1

No. 25 million light years is a long way. To put it in perspective, that's 250 times the diameter of our galaxy. The fact that you need a telescope to spot it should give you a clue - it's spewing out vast amounts of radiation (or, it was, 25 million years ago), of which visible light is just part, but it's still barely visible with the naked eye. Even if it was emitting 1,000 times as much gamma radiation as visible light, it would be a negligible amount.

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Money by udachny · 2011-09-05 05:44 · Score: 2

Here is a great idea for improving the economy - stimulate more R&D, research and development, more supernovas need to be found, more telescopes must be built, put the money into this, get some engineering going. Fuck wars, lets build telescopes. Build more telescopes, build more space ships. Need more engineers for this, need more scientists, need more architects, need more of everything. Build more, spend on building, stop wars and get going.

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1. Re:Money by mikech2000 · 2011-09-05 06:03 · Score: 3, Informative
  
  Sorry but discovering interesting things about the universe offers no ROI during the next fiscal quarter.
2. Re:Money by dotancohen · 2011-09-05 06:14 · Score: 2
  
  Here is a great idea for improving the economy - stimulate more R&D, research and development, more supernovas need to be found, more telescopes must be built, put the money into this, get some engineering going. Fuck wars, lets build telescopes. Build more telescopes, build more space ships. Need more engineers for this, need more scientists, need more architects, need more of everything. Build more, spend on building, stop wars and get going.
  Go check how many space exploration lobbyists exist in Washington then check how many petroleum and military-tech lobbyists exist in Washington. Now try to rephrase your suggestion in terms of oil usage and military technology.
  
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Re:Convenient by Noughmad · 2011-09-05 05:46 · Score: 2

Depends, is there a tinfoil commercial too?

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Re:Gamma rays? by Iskender · 2011-09-05 05:50 · Score: 1

You're probably joking, but let's put it like this:
The star Betelgeuse could go supernova tomorrow or a million years from now. It's about 600 light years distant. The consensus is that it won't pose any danger to us.
The supernova we're discussing here, SN 2011fe, is about 20 million light years away from us. So if this supernova was 30 000 times closer to us it would most likely still be safe. =)
It's actually naked eye visible? by NotSoHeavyD3 · 2011-09-05 06:08 · Score: 2

Really? I mean I know the Andromeda galaxy is normally the furthest naked eye visible object and that's 2 million LY away. (This thing is 10X further and is still naked eye visible? That's amazing.)

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Meh by MrL0G1C · 2011-09-05 06:22 · Score: 1

Computer says no :-(
http://www.metoffice.gov.uk/weather/uk/se/london_forecast_wind.html

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it's in our reference frame by rubycodez · 2011-09-05 06:32 · Score: 2

The star that exploded is not moving at relativistic velocities in relation to us, and the non-inertial part of our and its reference frames are tiny too. It exploded 21 million years ago in our reference frame.
I'm @south. by yorugua · 2011-09-05 07:43 · Score: 1

I'm in the southern hemisphere, you insensitive clod! ok, maybe next time.
1. Re:I'm @south. by quenda · 2011-09-05 15:13 · Score: 2
  
  I'm in the southern hemisphere, you insensitive clod!
  That's OK. We had front-row seats for the 1987 supernova, a mere 168,000 light-years away, and visible to the naked eye.
  The previous one brighter was in 1604.
  http://en.wikipedia.org/wiki/SN_1987A
Re:Gamma rays? by Anynomous+Coward · 2011-09-05 07:50 · Score: 1

Hmm. It would be quite dangerous to us - some sorry fellow on the road and me - as I'd surely notice it driving home late in the evening and would be terribly distracted.

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How Long Do They Last? by Doc+Ruby · 2011-09-05 08:08 · Score: 1

I'm always curious about these observed supernova events. How long do they last in a well-defined event? Even if not visible to the unassisted human eye at cloudless night, how long by optical telescope? How long can the more subtle beginnings and endings be seen with radar telescope and our more advanced instruments?
Milliseconds? Minutes? Hours? Days? Months? Lifetimes? Planetary lifetimes? Depends on the supernova?

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1. Re:How Long Do They Last? by mojo-raisin · 2011-09-05 09:23 · Score: 4, Informative
  
  I don't know how long it lasts, but its daily intensity is being plotted here. From what little I've read, it can be expected to increase like this for ~14 days from the initial explosion
2. Re:How Long Do They Last? by thrich81 · 2011-09-05 09:30 · Score: 1
  
  The "event" of spectacular brightness lasts a couple of months or so and depends on the type of supernova. As far as the "endings" are concerned, the remnant debris can be seen for thousands of years at least -- the Crab nebula and its central pulsar is a supernova remnant from a supernova seen on Earth in 1054 AD.
3. Re:How Long Do They Last? by jmichaelg · 2011-09-05 10:34 · Score: 5, Informative
  
  This web page has a graph that shows the different light curves for type 1 and type 2 supernovae.
  A Type 1 supernova reaches it's peak light output around 10-15 days of the initial explosion and then exponentially decays over a period of years. As the curve is exponential, a good chunk of the luminosity is lost within a couple of months and then the loss rate tapers off somewhat.
  A type 2 supernova reaches its peak output in a few days decays, plateaus for a few months and then begins decaying again over a span of years.
  The mechanism behind a type 1 is fairly well understood but the variation in modeled and observed luminosity is greater than 2%. A paper a few years back suggested that the variation might be evidence of dark matter but subsequent modeling has shown that the 2% variation can be accounted for by where the observer happens to be relative to the explosion as the explosions aren't symmetric.
It happened 21M years ago in our frame too by drnb · 2011-09-05 08:56 · Score: 1

From our reference frame, this happened hours ago. The summary is correct. You are not.
It happened 21 million years ago in both the frame of reference of the solar system of the star gone nova and in the frame of reference of our solar system. We may have only just seen the evidence but we know it is 21 million light years away, so we know when it happened. I don't think distance changes one's frame of reference, I think only motion does. Two travelers in our system, one at 0.25c and the other at 0.5c have different frames due to their respective velocities, not distance from the nova.

I will now patiently wait for actual physicists to correct my erroneous and simplistic belief. :-)
Velocity, not distance, brings relativity by drnb · 2011-09-05 09:06 · Score: 1

I'm pretty sure it exploded about 21 million years ago.
In the star's POV, yes. In our POV, it just exploded.
No. Well not unless the speed of light is infinity all of a sudden. Given the speed of light we all know and love, and an object 21 million lightyears away, an event we observe happened 21 million years ago. IIRC its the velocity of the observer, not distance, that brings relativity into play.
1. Re:Velocity, not distance, brings relativity by gstrickler · 2011-09-05 16:26 · Score: 1
  
  No, there is a reason we call it space-time. Causality shows that relativistic time frames (not time dilation) apply at a distance. In fact, they apply at any distance, but for local phenomenon are so close that the different frames can usually be ignored. He's a post that explains it more fully.
  
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Re:Gamma rays? by Anonymous Coward · 2011-09-05 10:16 · Score: 1

Would you and every other fool kindly stop abusing "exponentially"? It means O(e^bx), not O(x^2).
It's quadratically lowered risk the further away you are!
Re:Supernova are generally 1B LY away?? by RockDoctor · 2011-09-05 12:52 · Score: 1

Yeah, it's a really silly thing to say. A billion LY radius sphere contains about 125000 times the number of stars as a 20-odd LY radius sphere. The *average* location of an event occurring randomly within a unit sphere is going to be about 0.79 from the centre of the sphere.
I think they probably mean that the average range of detected supernovae is around a billion light years, which would imply that the range to which a Type 1 "standard candle" supernova can be readily detected is about 1.25 billion light years.
(I am, of course assuming use of a colonial billion, not a standard billion.)

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Re:Supernova are generally 1B LY away?? by gstrickler · 2011-09-05 13:04 · Score: 1

He said (this might not be word for word) "Most of the supernova discovered by the Palomar 48 inch telescope are over 1B LY away". They're also discussing only type Ia supernova, not type II (which SN1987A was).

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Betelgeuse by Anonymous Coward · 2011-09-05 14:47 · Score: 1

I hope I get to see a Betelgeuse Supernova in my lifetime. that would be pretty damn cool, and you wouldn't need binoculars to see that.
Understanding space-time and causality. by gstrickler · 2011-09-05 17:10 · Score: 1

For Earth, it happened a week ago. Space and time aren't separable, stuff doesn't merely move through space, it moves through space-time. We can only refer to time separately when looking from a specific reference frame. Only from the space-time of the supernova did it happen 21M years ago, and we're not in that space-time. From ANY other reference, it DIDN'T happen 21M years ago, it happened less than that, or (for distances greater than 21M LY from the event) it hasn't even happened yet. Thus it's both misleading and meaningless to say it happened 21M years ago. It happened last week, and it is/was 21M LY distant in space-time.
Because we can estimate the distance, we can calculate that in it's frame of reference it happened 21M years ago, but that frame of reference is meaningless to anything outside the space-time of the progenitor star, thus it's meaningless to us on Earth. Saying it happened 21M years ago for us requires a concept of universal simultaneity (a universal "now"), which would require that information be transmitted across space-time instantly. This information transfer would be infinitely faster than than the speed of light, which would violate all the laws of physics we know.
For an example of how the speed of light and causality work in this interconnected fabric we call space-time, see my other post.

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Oblig by AP31R0N · 2011-09-06 00:22 · Score: 1

Do not look at supernova with remaining good eye.

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Why isn't this much brighter? by grumpygrodyguy · 2011-09-06 03:38 · Score: 1

I remember reading about supernovae being so bright they could be observed during the day, brighter than Venus for instance.
From History of supernova observation

The supernova SN 1006 appeared in the southern constellation of Lupus during the year 1006 CE. This was the brightest recorded star ever to appear in the night sky, and its presence was noted in China, Egypt, Iraq, Italy, Japan and Switzerland. It may also have been noted in France, Syria, and North America. Egyptian physician, astronomer and astrologer Ali ibn Ridwan gave the brightness of this star as one-quarter the brightness of the Moon. Modern astronomers have discovered the faint remnant of this explosion and determined that it was only 7,100 light-years from the Earth.[7]
It looks like this one will top out at magnitude 9 at best, making it appear like a dim star at night. How is that this supernova, if it's so close to us, appears so dim?
Can anyone clarify this? I thought type I/II supernova have roughly the same energetic magnitude...so if this one is only 21 million light years away, why isn't it brighter?
Edit: Nevermind, I figured it out. 21 million light-years vs. 7,100 light-years (the example above) is 5 orders of magnitude. It's faint because it's very very far away.

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1. Re:Why isn't this much brighter? by gstrickler · 2011-09-06 07:40 · Score: 1
  
  And since you figured it out, why did you choose to post it rather than cancel it?
  Also, intensity decreases with the square of the distance, so brightness would be roughly 7.1K^2/21M^2 ~ 1.14E-7 the brightness, which is ~17 orders of apparent magnitude (5 orders of visual magnitude is a factor of 100).
  
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Sure it did. by Ungrounded+Lightning · 2011-09-06 04:14 · Score: 1

No the summary is not correct. It did not happen "hours ago" from any reference frame.
Sure it did - in a reference frame moving from it toward us at nearly the speed of light. B-) "any" is a very strong word when you're talking about reference frames and relativity.
However it's obvious that they're talkiing about "hours ago plus the light lag from the distance", i.e. the timescale of the obervability of the event.

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