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As we discussed it in this question, the Death Star can deliver a mind-boggling amount of energy. If it is capable of blowing up an Earth-sized planet, this means the equivalent of the annihilation energy of over 1,200,000,000,000 tonnes of antimatter. In comparison, nukes measure on this scale in the gram range (the one used at Hiroshima being under one gram). This means, even if the shot gets a million times weaker due to distance, it is probably still enough to kill all multi-cellular life on a planet.

Regarding this, how much is the maximum effective range of the Death Star? By effective I mean that even if it does not blow up a planet Alderaan-style, it delivers enough damage on a planetary scale to effectively cripple a planet.

Is there any related information in the expanded universe?

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Lasers cannot blow up planets. The weapon they are using is not a laser. Lasers cannot create antimatter from matter. It would need to be a particle weapon that is made from antimatter, directed at a planet, annihilating the planet upon contact and creating new antimatter so the entire planet is destroyed. Otherwise the rubble from the explosion would destroy the Death Star as well... –  Thaddeus Jul 8 '12 at 23:52
@Thaddeus: I didn't say it was a laser, Kevin edited it in. –  vsz Jul 9 '12 at 3:10
This is a physics question, assuming that it is a plain laser. I know a flashlight behaves according to square inverse, but I'm not so sure how lasers behave... even with square inverse, it's going to have to be more than a few AUs before I'd want to be in the crosshairs. –  John O Jul 9 '12 at 16:28
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2 Answers

For my understanding, the effective range should essentially be several AU. Considering the main weapon is a laser, its effectiveness won't degrade with distance other than losing its concentration (like a laser pointer or flashlight: the further away the target spot is, the bigger the area being lighted). We don't know how focused it is (i.e. how much power is lost over a given distance).

According to this discussion, the Technical Journal of the Imperial Forces states the effective range of the superlaser is said to be about 157 lightseconds, which is something like 47 million kilometers (29 million miles) or 0.3 AU (a third of Earth's orbit). Although I don't know how this effectiveness is defined (just destroy everything living on the surface vs. destroy the surface vs. blow up the whole planet). If the station is able to destroy a planet at that distance, the whole setting from the movie sounds a bit absurd, considering they risked getting hit by debris, while they could have stayed away a lot further.

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If it is actually just a laser, keep in mind that a laser is only effectively "focused" for a brief distance. The practical distance of the Death Star is likely optimized for some distance limited by the geometry of the focal array. –  Gorchestopher H Jul 9 '12 at 2:38
@Gorchestopher H: Still, a billion times less energy is enough to cripple a planet. This means the range could have theoretically be increased by several orders of magnitude, and still be dangerous on a planetary scale. Energy required to blow up a planet > 1000000000 * energy required to kill everyone on its surface. –  vsz Jul 9 '12 at 3:12
@vsz The limitation would still be the focus if it was a laser. Divergence continues on. –  Gorchestopher H Jul 9 '12 at 11:32
@Chad: Do you have a source about the antimatter stream? –  vsz Jul 9 '12 at 14:07
@Thaddeus: Ok, but this still not proves, and not even suggests that antimatter is involved in any form in the Death Star's weapon. –  vsz Jul 9 '12 at 14:28
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From Wookiepedia:

The power of the first Death Star's superlaser was estimated to have been more than 2.4×1032 watts, with an optimum range of 2,000,000 kilometers and a working range of 420,000,000 kilometers. Powerful enough to destroy a terrestrial planet, it was the most powerful energy weapon ever built at the time

And while the original source is not linked on wookiepedia I believe this is from The Essential Guide to Weapons and Technology

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Strange, that's less than 3 AU. Well, it's still much more than the range it was used in the movies (less than 0.01 AU). –  vsz Jul 9 '12 at 18:57
@vsz because it is not a lazer despite what it is called. It is a exotic matter beam... I am not sure how that compares to antimatter but based on its output I am guessing favorably on the side of destructive power. –  Chad Jul 9 '12 at 19:00
Even if it's a particle beam, there is no friction in space (at least not at such a small distance). As even a billionth of that energy is devastating, this should not limit the range that much. Or, maybe it starts "leaking" into Hyperspace, that's the cause of such a short range? –  vsz Jul 9 '12 at 19:17
@vzz - Contrary to popular belief space is not empty just sparse. There is lots of dust, debris, and hydrogen it is just so diffuse as to seem empty. But over long distances those little particles would siphon off significant power. –  Chad Jul 9 '12 at 19:23
Also consider it getting harder to hit targets further away, as you'll have to include their trajectory as well as your own. At some distance your aiming might simply be not good enough anymore to ensure a hit at all (it might take some time to do the calculations, but you have to aim properly as well). –  Mario Jul 9 '12 at 21:08
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