Hi all, I think there is a post on this somewhere that is accessible via google but somehow too hard to find on this site. Anyway, if a nuclear explosion went off in deep space, I think the following would happen: There would be a large burst of energy. All photons from Gamma to Radio would be emitted. The light from a nuclear blast is intrinsic to the energy of the nuclear explosion itself, so one should also see a bright fireball in the optical range. It should also persist for several seconds or more. A nuclear blast in the atmosphere of the Earth certainly persists for dozens of seconds, so I would expect a nuclear explosion in space to exist on a comparable timescale. It would be like a mini-sun for up to a minute, maybe 30 secs, I'm not sure, but it would be on this timescale. There would also be Alpha and Beta rays, and neutrons, so there would be large numbers of these particles released. They wouldn't be seen with the naked eye, but they would cook anything nearby much more quickly and strongly than a microwave. Finally, there might be some heavier nuclei ejected from the nuclear erxplosion. All expulsion of matter or photons would be spherical. There would be no mushroom cloud, shockwave, sound, etc. as such effects would need an atmosphere, and that is completely lacking in deep space. There would be heat, but it would NOT be due to the temperature of any gas; it would be the heat of the infrared photons produced by the energy of the explosion. How am I doing with imagining what a nuclear blast would look like in space? Other posts on the internet mentioned a dim flash that is over quickly due to a lack of atmosphere, but I think this is incorrect. I think the trememndous energy in a nuclear explosion would have plenty of energy for plenty of optical photons.