If someone detonates a one megaton nuclear bomb in space, how far will it be visible to the naked eye? Of course, I am aware that there is no medium in space that can glow, so all the light would come from the bomb itself. In any case, a significant part of the energy is emitted at frequencies that are invisible to the eye. If I stand in a good vantage point and look in the right direction, can I see, say, a bomb exploding in the distance of Jupiter? In astronomical terms, I use 6 magnitudes as a limit for visibility.
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3 Answers
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Start with this figure:
Assume the entire mass of the devices is heated with the energy from the yield in 10-100 nanoseconds.
Estimate a temperature and assume it's a blackbody. The size is that of the initial device.
Use Planck Law to compute the radiances (Watts per square meter per steradian per hertz), convert that to the wayward SI base unit: The Candela (luminous intensity).
Use Stephan Boltzmann's law to compute the temperature derivative with respect to time, and average the result over a human eye integration time.
Post your answer.
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Consider that most large explosions have an intensity proportional to 1/(distance-squared), very much like the distribution of sound. As for visibility itself, this can depend on how much of the energy goes to visible light, as opposed to invisible light, to particles, and to full atoms. If you have the original light power and required intensity, distance for a spherical distribution should be similar to any other spherical wave distribution.
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As far as I know, assuming that there is no disruptions that fully or partially block out the light from the blast (for example, cosmic dust), the brightness from the explosion should be about the same as one of such on earth, which is comparable in brightness to the sun, depending on what you mean by 'a good vantage point', as well as the tonnage of the nuclear warhead, you should be able to see it on jupiter while standing on earth, but an interesting thing to note is that you would not be able to see the light emitted immediately, rather, it would take about 43 minutes for the light to reach earth from jupiter, assuming that the dense and thick atmosphere of jupiter does not block out the light from the blast. Additionally, that is assuming that the warhead is large enough such that the emitted light could be observed; it is incredibly hard to actually see the blast with a naked eye, as a 1 megaton would only generate a visible blast radius of 1km, whereas the largest bomb ever made could only generate a 8km lit radius, so it would be a stretch to actually see it from earth with the naked eye, but with a decent telescope, you should at least be able to see a really bright spot on jupiter
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2$\begingroup$ Much of the initial "light" from a nuclear warhead explosion is in the form of x-rays. On Earth, those x-rays are absorbed by air, and they heat a vast volume of it to incandescence, creating a "nuclear fireball." But, out in the vacuum of interplanetary space, all that energy stays in the form of invisible x-rays as it heads off to infinity. Nowhere near as much blast, and nowhere near as much visible light as when the device is exloded in atmosphere. $\endgroup$ Commented Mar 6, 2023 at 1:15
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$\begingroup$ I didn't mean that the explosion would happen on Jupiter, I meant that the explosion would happen at a distance of, say, 50 light minutes in empty space. By good vantage point I meant a night in the countryside and the explosion happening in zenith. I can imagine that the plasma created by the explosion expands at high speed and, over time, also cools down. The question is actually how big the plasma ball is when the radiation it emits is in the visible light range. $\endgroup$– TimppaCommented May 17 at 16:13