# space - Is there a minimum safe distance to watch a supernova?

Consider that humans now have technology to travel around the galaxy at will.

Hyperspace, warp speed you name it.

There is a distance in which they can watch a supernova as a form of entertainment AND not be harmed in the process? As we do with the sunrise (in terms of experience). It can be from a planet in another system or a ship.

Edit: consider a special kind of glass-like material capable of filter some radiation. But not all of it. The risk is the same as we taking a sunbath without sunscreen.

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• @KeizerHarm it just for cozy flash observation, not an extinction event(the flash, but nebula aka spilled matter is more interesting and hard question), 10x for a second with glasses and cloth won't harm that much and it 1/3 the distance, add 10% tint to a glass and get 1/3 closer. Not sure about spectrum. But okay seems current answer is enough for OP so it all irrelevant Sep 2, 2021 at 15:16
• @KeizerHarm and at a distance it will be days long event(observation), so, exact distance is hard to tell, so I probably should have dug deeper, and more reliable data on duration of the process, and how it evolves, as visible light is secondary emission, so it was just upper estimation, practical distances are shorter. Was a bit misleading, and being mislead by. Let me know u read, I'll delete those comments, should have been done a better job googling or a better memory Sep 2, 2021 at 15:24

The actual explosion of a supernova isn't really all that much "entertainment." It's an extremely bright flash. The formation of the nebula might be interesting. But that is a much longer process, starting at months and upwards to 100s of years. And, if you are far enough away as not to be fried by the initial flash, you will need very good telescopes to see the nebula expanding.

So the supernova that produced the crab nebula was observed on Earth in the year 1054. Now, through some very good telescopes, it looks like the following.

https://en.wikipedia.org/wiki/Crab_Nebula

It would be pretty interesting to be able to watch that form. The problem is, it took 1000 years to get to that stage. Your audience would need to be quite extremely patient.

But they have hyperspace you say? OK. There is not a single distance to watch from. What you do is arrange to start at a very long distance from the explosion. In this case, about 1000 light years. Then, on observing the initial explosion, you start moving towards it in hyperspace. The idea is, you stop and observe for a short time. Then move closer, stop and observe, move closer, etc. What you wind up with is a "movie." You start with the initial flash, then the "firework" expands out as you move closer. Because hyperspace is faster than light, you adjust things so that over about 30 seconds ship-time (or 4 hours to allow a nice dinner and drinks), you move that 1000 light years closer. That means the apparent expansion takes 30 seconds, because you are travelling "upstream" of the light.

One interesting feature of such a scheme is, you can watch it many times. And from many angles. The light is "crawling" along at light speed. You can hyperspace over and go through the movie as it expands. Since the nebula takes 1000 years to get that big, you have lots of time to watch it many times from many angles.

• Wow. That's perfect. Sep 2, 2021 at 14:02
• Take care to avoid causality violating paradoxes if there are any other people doing the same thing in their FTL ships!! Sep 2, 2021 at 14:14
• Assuming relativity is correct, then FTL is unavoidably also a time machine. If relativity is not correct, then who knows? Sep 2, 2021 at 17:56
• If you choose a proper starting point and sublight velocity towards the explosion, you can assemble your "movie" entirely in normal space. For example, to make a 10-minute movie of the Crab nebula forming, you'd start about 967 light years away from the nebula, so you can catch the supernova flash, and then speed up to $\frac{\sqrt{2583233483270399}}{50825520}c = 0.999999999999999806444131652011982848833673483577405269404967507c$ in the direction of the nebula.... Sep 2, 2021 at 21:44
• @RossPresser of course by doing so at the end of your 10 minute movie you will have found that everyone roughly stationary to you during that time will have died about 3.5 million years ago, give or take a couple millennia.
– eps
Sep 2, 2021 at 23:52

## Safe distance estimates vary

Now, if you add a glassy shield, it would depend upon how effective this shield is. Blocking 75% of radiation means only 1 part in 4 harmful radiation gets past your shield - this would allow you to be twice as close since the radiation falls off proportional to distance squared.

If you had a 100% effective shield against ionizing EM radiation, you still have limits unless you could shield against neutrinos since they easily pass through planets and stars and presumably your shield - and there are a massive number of neutrinos in a supernova. So much so, that even though interactions between a neutrino and your body is very rare, you can be killed with a few A.U. of a supernova from neutrinos alone.

• See also what-if.xkcd.com/73 which reveals that A supernova, seen from as far away as the Sun is from the Earth is brighter than The detonation of a hydrogen bomb pressed against your eyeball Sep 2, 2021 at 21:47
• Obligatory xkcd,yep Sep 3, 2021 at 9:37
• @RossPresser You omitted the part about said supernova at 1 AU being brighter than said bomb at eyeball-distance by nine orders of magnitude. Sep 3, 2021 at 17:39
• @cmaster-reinstatemonica - A non-lethal dose of neutrinos does not mean a safe dose. Just because you are 10 AU away from a supernova (and well outside the star) does not mean that you are safe from neutrino radiation - so even the 100% effective shield against ionizing radiation I mentioned would not really make you safe. You would also be cooked by the infrared or visible light at that distance. I supposed it was obvious to me that you would also have to shield against most of the non-ionizing radiation too. Sep 3, 2021 at 19:00
• The outer layer of a star ready to supernova is a pretty good vacuum - but probably not the best observation location for the supernova :-) Sep 3, 2021 at 19:42