# How visible are nuclear explosions? - spoilers for BSG Season 2 **URL:** \ **Category:** Factual Questions\ **Created:** [October 22, 2006, 11:52am UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436 "2006-10-22T11:52:41Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 22, 2006, 11:52am UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/1 "2006-10-22T11:52:41Z")
Spoiler space ahoy! . . All of this has been spoiled before, all of this will be spoiled again - when it gets broadcast over here. . . . At the end of Season 2 of BSG, the colonial fleet is in orbit around New Caprica. The spaceship Cloud 9 is destroyed in a nuclear explosion. A year later, the Cylons turn up, having detected the explosion from a light-year away. How does this compare with modern astronomy? The distance / time is right, but how about the sensitivity? Could we detect a (say) one megaton explosion a light-year away? ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 26, 2006, 7:39pm UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/2 "2006-10-26T19:39:07Z")
My one allowed punt ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [October 26, 2006, 8:12pm UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/3 "2006-10-26T20:12:26Z")
[QUOTE=Quartz] My one allowed punt [/QUOTE] If we had an appropriate instrument already pointed in the right direction from as close as one light year, yeah. Visible to normal skygazing other than that, I don’t think so, but have no math to back that up. Tris ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [October 26, 2006, 8:48pm UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/4 "2006-10-26T20:48:59Z")
We’d probably have to be looking at just the right time- I don’t know if nuclear explosions are luminous enough for long enough to be visible from a light year away, except for the initial flash. I’d think that something like a neutrino burst(are neutrinos given off by nuclear weapons?) would be a more plausible way to describe how the blast was detected. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 26, 2006, 8:53pm UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/5 "2006-10-26T20:53:23Z")
1 megaton TNT is 4x10[sup]15[/sup] Joule. I’m not sure how fast this energy is released, or in what form. But if we assume it takes 10 seconds, and the spectrum is similar to the sun (i.e. ~6000 degrees), then it would be 10[sup]-12[/sup] times the brightness of the sun. At 1 light-year, the sun’s apparent magnitude is about -2.5. Factor of 10[sup]12[/sup] is 30 magnitudes, so the apparent magnitude of the explosin would be about 27.5. Telescopes today can detect stars that faint, but I think it takes a long exposure to do so; I’d guess detecting a 10-second flash of that brightness would be very difficult, if not impossible. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 26, 2006, 9:20pm UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/6 "2006-10-26T21:20:22Z")
Surely the temperature would be millions of degrees? The sun’s core is constrained by its mantle; there’s no such restriction on a bomb. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 26, 2006, 9:51pm UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/7 "2006-10-26T21:51:28Z")
I guess the actual core of the explosion may be millions of degrees. But my WAG/assumption was that most of the energy will go into heating the surrounding material into a \<10,00K plasma, which would then radiate the energy as photons. Besides, assuming 6000K made the calculation _much_ easier… ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [October 27, 2006, 12:11am UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/8 "2006-10-27T00:11:06Z")
Most of the energy released by a nuclear device detonated in a vacuum is emitted as soft x-rays. This is from black-body radiation. Most of the effects seen when a nuclear device is detonated on the Earth are due to complex interactions with the atmosphere. The atmosphere absorbs and reemits the energy from the device, over and over again, creating the fireball. The atmosphere is relatively opaque to soft x-rays. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 27, 2006, 4:04am UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/9 "2006-10-27T04:04:02Z")
> [@](#): > > I’d think that something like a neutrino burst(are neutrinos given off by nuclear weapons?) would be a more plausible way to describe how the blast was detected. I don’t know anything about Cylon telescope technology, so I can’t answer the main question. But I can say that neutrinos are never going to be the easiest way to detect something. It’s very hard to detect neutrinos, but it’s very hard to fail to detect photons. And there will be neutrinos produced in most fusion bomb designs, but not in a pure fission bomb. In either case, there will probably be neutrinos produced as the fallout decays, but that’ll be a slow, protracted process. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 27, 2006, 4:44am UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/10 "2006-10-27T04:44:30Z")
[QUOTE=mks57] Most of the energy released by a nuclear device detonated in a vacuum is emitted as soft x-rays. This is from black-body radiation.. [/QUOTE] What temperature would you say this radiation would be? I suppose an X-ray burst might be easier to detect. But if this explosion happens near a star, it would be extremely difficult to distinguish from a flare. I don’t think you can do it by looking at the spectrum - you’d need to resolve the explosion spatially from the star. We don’t have any X-ray telescopes that comes even close. I guess you’d have the same problem with visible light too, come to think of it. You’d need something specifically designed to detect dim objects close to bright stars, like the proposed Terrestrial Planet Finder mission. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [October 27, 2006, 6:00am UTC](https://boards.straightdope.com/t/how-visible-are-nuclear-explosions-spoilers-for-bsg-season-2/377436/11 "2006-10-27T06:00:49Z")
[QUOTE=scr4] What temperature would you say this radiation would be? [/QUOTE] [Elements of Thermonuclear Weapon Design](http://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html) > [@](#): > > By applying the blackbody radiation laws (see Section 3.1.6 Properties of Blackbody Radiation) we can determine the corresponding radiation intensities and temperatures: 9.8 x 10^6 K and 5.3 x 10^16 W/cm^2 for Mike; and 2 x 10^7 K and 1.0 x 10^18 W/cm^2 for the W-80. The radiation pressures are 73 and 1400 megabars respectively. So about 20,000,000°K, although the article does say some devices will reach high as 100 million °K. There’s an interesting discussion of blasts in the high atmosphere here: [Descriptions of Nuclear Explosions](http://www.cddc.vt.edu/host/atomic/nukeffct/enw77b1.html): > [@](#): > > The TEAK explosion was accompanied by a sharp and bright flash of light which was visible above the horizon from Hawaii, over 700 miles away. Because of the long range of the X rays in the low-density atmosphere in the immediate vicinity of the burst, the fireball grew very rapidly in size. In 0.3 second, its diameter was already 11 miles and it increased to 18 miles in 3.5 seconds. Teak was at ~48 miles. Fireball growth is dominated by Earth’s magnetic field in tests at 200+ miles altitudes, which seems to be about as high as anyone’s gone. To really be sure of what a nuke would look like in _space_, we’d have to set one off outside the magnetosphere.