It has been argued that Alderaan was shielded, and that it resisted the Death Star superlaser for a fraction of a second. Some support for this contention is found in the destruction of Alderaan from the original version of Star Wars, as seen at right. The superlaser seems to be redistributed around a sphere far larger than the planet itself, as if the beam were reaching around the world to crush it. All things being equal, a planetary shield would be just about the only viable explanation.
However, the Special Editions of the films superceded the original versions, and thus arguments which required the original version of events became unsupportable. One of the events replaced was the Alderaan destruction scene, and the original effect was thus excised from the canon. Below, we see the hit as it appeared in the Special Edition:
As you can see, the superlaser struck the planet, produced a bright flash, and then the planet started to go. At no point was a planetary shield observed, or even inferrable. Nonetheless, some continued to argue that it was there based on the original version of the film, or even by claiming that the illuminated clouds were evidence of a shield. With the advent of the DVD releases the claims have become even more absurd. First, let's take a look at some tight views of the first few frames:
There are a few noteworthy differences between the DVD version and the SE version. For one, the DVD version is far crisper than any prior version. Second, the next-to-last frame in the DVD version above shows the planet in a "white-out" state, whereas the SE version offers more detail. And, that little mystery object in the upper left is more readily visible, to the point that even my visually-challenged opposition started to agree that it was present.
Still, however, there is nothing to suggest a shield. Nonetheless, the most frequent claim being made by the opposition at the SD.Net BBS is that there is a shield glow existing visibly outside the Alderaanian atmosphere. This, however, is untrue. First, let's take a tight view of Alderaan, alone in space:
As you can see, we have a sphere partially lit from the left. We know this because the above is not almost perfectly circular, as a planet would appear in a two-dimensional image. The terminator between night and day is visible on the right-hand side, and given the angles we can tell that the sun ought to be located millions of miles to the left of frame, somewhat upward, and some distance behind the camera's viewpoint.
Now, we take the image above and ramp up the brightness and contrast:
At these levels the planet's surface is little more than a white ball. You can also see some interesting bluish haze areas, predominately around the left and right of the white area. We'll come back to those later. For now, however, we can simply create a fixed-diameter circle around the left side of the white ball of the planet:
The above shows us a red mask around the outside of that 126px circle. Just for safety's sake, we can even put another circle around the blue haze area on the left:
We thus have a 136px circle around the planet and the original red masking, with anything outside the circle colored green for clarity. We can even remove the red circle from that position so we have a nice yellow outline of the planet. Just to check ourselves, let's overlay that on top of the original Alderaan image:
The fit is imprecise by a pixel or two at the upper left, but we don't require excessive precision for what we're about to do. Remember, the opposition is claiming that the glow from the superlaser hit is outside the atmosphere of Alderaan on the right-hand side. Or, as it was put by "Vympel" of StarDestroyer.Net fame, "it's quite obvious that the shield is extra-atmospheric in nature, the glow on the right-hand side extends well beyond any possible atmosphere of the planet."
Let's take our yellow circle and overlay it on the frames in question:
In neither case does the glow extend outside the atmosphere on the right . . . neither image shows the glow even touching the yellow circle's interior, much less bypassing the circle altogether. And, the frames which follow show an orange fireball on the right, by which point the claimed shield would not be in existence.
In short, we have another instance of the most popular Warsie myth being based on non-canon silliness and the attempt to see what one wants to see by simply misunderstanding the canon.
Those who wish to argue for a shield's existence must therefore prove it. This, however, is an impossibility. At no point is the thesis of superlaser deflection by shield supported by the canon DVD Edition, or any other canon data.
A reader pointed out the following via site feedback:
"Naboo didn't have shields either, for that matter. Yet in the oppressive Empire, which did everything it could to ensure no-one could resist it's might, Alderaan had the chance to build shields all over it's surface? ... No."
The above makes sense. The only time when we might've expected planetary shields to be employed without danger of Imperial retribution would've been during the Clone War. Unless they appear in Episode III canon materials (which, per all spoilers, does not seem to be likely), then they don't exist in Star Wars.
The Alderaan Shield Fallacy is subscribed to the most by those who wish to define the superlaser in a certain way, and thus the point is constantly disputed. Numerous angles of attack have been employed, many of which are contrary to one another. Some are just variations on prior themes. Others are just odd. Here's the main list from the SE days, along with responses from the same SE sources. DVD-era objections and responses will be added later.
1. It has been argued that the term "defenses" (referring to Alderaan's being as strong as any in the Empire) must imply a shield.
The above "Alderaan 'Defenses' Argument" is based on two things. The first is Leia's claim to Tarkin in ANH that Alderaan is peaceful and has no weapons. Second, there is the Chapter VIII novelization quote from Vader, given in full below:
"The defense systems on Alderaan, despite the Senator's protestations to
the contrary, were as strong as any in the Empire. I should think that
our demonstration was as impressive as it was thorough."
There is an inherent flaw in the argument, however. Those who make such a claim are picking and choosing among the materials in evidence. Leia said they were peaceful and without weapons (or "standing armies", in the novel). Vader then explains that in spite of what she said, their defenses were indeed strong. Therefore, all we know is that, despite Leia's protestations, Alderaan is as well-defended as any world. However, we don't really know what that means. It could be orbital defense outposts, fleets, ground-to-surface weapons, or a naked guy with sharp sticks. Tarkin follows up on Vader's comment with a nod, stating:
"Now that their main source of munitions, Alderaan, has been eliminated,
the rest of those systems with secessionist inclinations will fall in line quickly
enough, you'll see."
The leap made by the objector would be that Leia's "no weapons" statement from the film and the novel's "strong defenses" were both valid, but that the bit wherein Vader overrides Leia's statement, and the bit about Alderaanian munitions, are both to be ignored. Further, they ignore the fact that the Rebel fleet in RoTJ is said, in the novelization, to include "Alderaanian gunships" (Ch. IV). Thus, we know that Leia's claim was false, and that Vader's "defense systems" need not have referred to defensive shields.
However, even if one ignores the above, the leap to planetary shielding is still a far one. The quote does not demand or imply a planetary shield. One wonders what's wrong with the old fashioned way of defending, where defenders shoot down the enemy ships with planetary weapons (surface installations, orbital platforms, etc.), and fight them with their own fighters and starships, and armies on the ground. That is to say, there is zero evidence that planetary shields form a part of a Star Wars planet's defenses. (Small theatre shields, such as the one employed at Hoth, could possibly be used to cover major cities, but that is not what is being argued for by the opposition.)
It's also worth noting that the EU, which the SD.Net folks rely on so much and have tried to shape in favor of their arguments, also rejects the idea of a shield at Alderaan, despite the fact that it claims shields for other planets. The Dark Empire Sourcebook states the following on page 125:
"Alderaan had no shields of any kind, so it was utterly vaporized. A shielded planet that is overcome by a superlaser may "merely" have its entire surface burned off or split into several pieces. Note that planets don't have to be destroyed to be rendered uninhabitable."
Further, the Death Star constitutes a new form of attack, simply because of its far greater reach compared to the normal weapons ranges of Star Wars vessels. The ion cannons, orbital platforms, fighters, starships, and so on that would logically comprise the majority of a major world's defenses in Star Wars are rendered useless by the long-range, one-shot-one-kill superlaser. It lacks the finesse of a well-coordinated fleet assault on an enemy world, but makes up for it by sheer utility.
As analogy, ponder historical examples. Long ago, a castle was thought to be an impenetrable fortress . . . you couldn't hope to destroy it straight-away, since even if you managed to push the defending army back behind the walls, you were stuck with a siege situation. Now imagine that the attackers acquire an F-15. The castle will be destroyed in short order. It defeats the castle defenses by attacking in a totally new way . . . from the air. Similarly, there are the examples of the Luftwaffe during the Battle of Britain, or Germany's V-2 rockets, both of which showed air power nullifying Britain's surface-oriented defensive advantages of separation by water and a powerful navy quite easily by utterly bypassing them. Even ICBMs fall under this sort of category, since instead of there being bombers that one's air defenses can shoot down, you've suddenly got nuclear bombs which effectively drop themselves from orbit.
Little wonder, then, that the remark is made aboard the Death Star that their demonstration was as impressive as it was thorough. The Death Star was a weapon of sheer terror . . . there was no defense against it no matter how well-defended you thought you were, and that was the point.
2. It has been claimed that when
the superlaser hits Alderaan, there is an extra-atmospheric halo effect, which
supposedly proves a shield.
|That simply isn't the case. The image to the left shows the result of drawing a 103 pixel circle over the scene. As you can see, the entire planet is well-contained within the circle, and there is nothing beyond the circle besides the superlaser . . . the glow on the right side doesn't even touch it. Those who've made the claim simply failed to note that the planet's terminator between light and dark sides was not the surface of the planet.|
Further, the bright glow . . . the supposed 'halo' . . . is actually a brightening of the clouds, at least until the target area is so bright we can't see anything anyway. Even then, it is the clouds that glow the most at the farthest points from the target zone:
Note how the glow happens to follow the line of the clouds, just as we would expect from the diffraction of a very bright light source (brighter, even, than the refraction of sunlight), such as one would get from something causing a planet's destruction. For some reason, we're supposed to believe that this is a planetary shield, doing a great job of keeping itself quite invisible, having been designed to re-radiate the energy of the superlaser beam in keeping with the local weather patterns. That makes no sense whatsoever.
What we actually do see is the superlaser impact against the surface of the world, with the blinding flash radiating outward, diffracted by the air and clouds. Anyone can witness such diffraction in action on a cloudy day, as the clouds glow thanks to the diffracted light filtering down from above. The same principle applies.
A shield is thus not the only explanation . . . it is, however, the worst possible one.
Further, there is no other shield type in Star Wars which operates in the "radiate the energy around the shield" way, a la Star Trek shields. That includes the shields of Imperial and Rebel spacecraft, earlier vessels such as Trade Federation ships and Naboo fighters, and even the tiny Gungan theatre shields which Mike Wong has attempted to use as proof of shield overlap capability in Imperial-tech planetary shields. Indeed, for the most part, Imperial-era shields were completely invisible.
(The one possible exception to the perimeter radiation shielding effect would be droideka shields in TPM, but in that case they were defending against their own reflected bolts. Note, though, that those shields were not seen to overlap (and apparently couldn't, given how droidekas always stood a sufficient distance away from one another). Those shields also had the decency to radiate the same spectrum as the offending bolts, as opposed to going from dull green to radiant white.)
For visual reference, below are images of the peculiar Gungan shields when in normal operation, and when hit. These are nothing like any Imperial shields we have ever seen . . . note the airglow and reflection of sunlight in the first image. (The only other time we've seen airglow in other shields were TPM's droidekas, along with when Anakin's fighter demonstrated it for a few seconds during shield reactivation.) Also, in reference to the radiation point above, note how the Gungan shield does not radiate energy along the shield perimeter, like Star Trek shields do.
In short, there is no extra-atmospheric halo, and the atmospheric brightening via diffusion is contrary to the shield hypothesis.
2a. It has been claimed that line-of-sight issues would prevent the atmospheric brightening from extending as far as it is seen to.
The above claim is inherently flawed because the presence of an atmosphere is not considered. Light scattering and diffusion are natural results of light's passage through an atmosphere. If that were not so, then instead of the sky appearing blue, we would simply see the sun in a black sky, as it appears on the moon.
Further, Alderaan would seem to have a particularly dense and/or thick atmosphere, which would be even more conducive to the refractive scattering and diffusion of light. Compare the blue-gray clouds of Alderaan, as seen from a range of about 77,000 kilometers, to a shot made by NASA's Clementine probe:
As you can see, the clouds of Earth are quite bright and visibly white, compared to the darker clouds (and also the hazy blue oceans) of Alderaan. The additional diffusion is readily observable and thus proven when one looks at Alderaan's terminator:
Note the visible atmosphere past the terminator in the brightness- and contrast-enhanced shot to the right, also visible (albeit less so) in the left-hand shot. The same result occurs no matter which frame you look at prior to the superlaser hit . . . we see hundreds of kilometers worth of diffusion. This suggests a natural atmospheric diffraction of light far greater than what one would expect from a planet such as Earth, as one can observe in the Clementine image above, or much more closely in the following shot:
(click for larger version)
The extra diffusion of a denser atmosphere is perfectly consistent with the diffusion effect observed when the superlaser hits the planet, and inconsistent with the shield hypothesis.
2b. It is claimed that the patchiness of the atmospheric brightening indicates a shield is the cause, as opposed to simple atmospheric brightening due to refraction.
That concept also fails to account for normal atmopheric effects. Clear sky, though looking blue from below, looks clear from above. The image above shows this quite nicely. The atmosphere only becomes opaque or even semi-opaque due to light hitting the atmosphere where water vapor concentration is highest . . . i.e. in the clouds. In a non-planetary example for the refraction concept, consider a laser beam, or flashlight beam. Shining it into the sky on a dark, non-humid night will be no fun . . . you can't see the beam well, if at all. If, on the other hand, it is a very cold night (or if you have a smoker handy), you can exhale in the path of the beam and end up being able to see the beam, due to refraction of the light. The clear sky did not refract well, but the clouds will.
|Nevertheless, there was sufficient light (and/or sufficiently dense atmosphere) to brighten even the clearest parts of Alderaan's atmosphere. In the image to the left, you can see how the left-side image, which comes from before the superlaser hit, is dark even in the dark blue, clear area. Meanwhile, the right-side image, from after the hit, shows that darker area as having become brighter, albeit not to the same extent as the clouds.|
Once again, that is perfectly consistent with simple atmospheric brightening and diffusion, but is inconsistent with a shield.
2c. It has been claimed that brightening on the left edge of the planet occurs when the ring is formed. This is claimed to be blue-glowing superheated ejecta from the surface, and thus is said to be evidence of shield failure.
The claim above is based on the image below:
What you're seeing is the frame from just before superlaser impact with the color inverted in some fashion, and superimposed on the fifth impact frame (i.e. the one featuring the first view of the ring, obviously). The claim is that the glow on the left edge of the world (minus the ring) is superheated and glowing material being flung into space. However, if we apply a similar maneuver to the second frame after impact (i.e. the second frame of glowing clouds), we get a similar additional blue sliver, as seen on the left below:
By the reasoning that the blue haze in the right-side pic is blue glowing debris being launched from Alderaan, then the blue haze on the left should be the same thing (not to mention the blue brightness increases that occur when the superlaser first hits!). However, the claimant argues that the second frame shows a shield effect. In other words, the same effect is given different causes, depending on what is thought to be more convenient for the argument. Instead, logic argues that the cause of the glowing slivers ought to be the same, which would allow us to not be inconsistent with our treatment of the evidence. The claimant's alternatives are that the shield was up the entire time (even in the fifth frame, by which point the planet has started to go), or that no frame shows a shield. Logically, it is the latter, which once again shows that the shield concept is inconsistent with the visual evidence.
Given that the left side of the planet remains visibly intact until well after the fifth frame, I submit that what we are seeing is atmospheric in origin, if not related to the overall brightening of the scene.
2d. It has been claimed that the superlaser changes color when over Alderaan, and that this proves a shield is present.
I really wish I could explain how that conclusion came about, but I have no idea. The superlaser beam was simply translucent, a fact not accounted for by the opponent who made the claim.
2e. It has been claimed that clouds do not diffract and diffuse light, but block it utterly. Thus, the cloud-brightening could only have come from above via reflection.
I've decided to go back and make reference to this objection, even though it's so ridiculous that I didn't feel a need to before. However, because this objection continues to be claimed as a devastating proof for a shield a year later, I decided to idiot-proof the page accordingly.
The flaw in the claim is a complete lack of understanding of . . . well, anything, really. This is the peril of some Vs. Debaters, who have evidently never been outside.
Clouds simply do not magically block out sunlight. Clouds are opaque, yes, but a cloudy day is not magically like night-time by virtue of the overcast sky. Instead, light comes through the clouds, because the ice crystals or water droplets that make up the cloud send the rays of light from above in all sorts of different directions. Depending on the cloud type, it could be bright or worryingly dark beneath the clouds. But, never have I seen the sky black during daylight hours, as is required by the objection, and I doubt you have either.
So, if the light from the sun one AU distant is not utterly blocked by clouds, then it strikes me as ludicrous to assume that a radiant point on the surface which likely features an intensity greater than the sun would fail to have light capable of penetrating the clouds. (Even atomic bombs feature greater-than-solar intensity . . . more on this can be found in Objection 7.)
3. It has been claimed that the novelization of RoTJ speaks of planetary shielding over Endor.
That is not the case. As the preface puts it, in clear confirmation of the canon visuals: "the view-screen depicted the battle station itself, the moon Endor, and a web of energy -- the deflector shield -- emanating from the green moon, encompassing the Death Star." The view-screen would've shown something like this:
Now, we are told in RoTJ chapter 4 that the shield "encompassed them both" on the Rebel display, but as you can see above that is not the case, and is contrary to the Imperial screen mentioned in the preface. It is thus a self-contradiction in the novel, and a contradiction with higher canon, which clearly sides with the preface.
4. It's been argued that Alderaan's rings prove a shield . . . i.e. that the rings appear because of shield failure.
That concept doesn't work. First, the ring appears after a point where it is clear that the planet itself is going up. Second, there is a second ring which appears after the secondary blast begins, by which point the planet appears to be in pieces. Third, no rings appear during any other shield failures. Fourth, the DS1 shield was a simple magnetic field, along with a few ray-shielded areas (at best), which is hardly the same sort of shield that is being claimed. And, last but not least, the DS2 produced rings despite being explicitly unshielded at the time of destruction.
Unlike other examples, the rings are not directly contrary to the shield hypothesis . . . but they certainly do not support it.
5. It's been argued that since shields are invisible throughout the original trilogy, lack of visible evidence for a shield does not constitute disproof.
Instead of trying to prove the existence of a shield, the claimant's position is to assume that shields exist (i.e. assume what they seek to prove), assume that one was operating on Alderaan, and then frame the argument in such a way as to make that assumption untestable. This claim is generally used in concert with an argument wherein the Empire could supposedly upscale known shield technology, or link a whole bunch of smaller shields together, or any other of a thousand fanciful sci-fi notions that might allow for a shield to exist. Or, in other words, the argued-for possibility is claimed as support of the untestable assumption.
That objection is wrong-headed, and seeks to put the burden of proof on the person arguing the negative, which is illogical. One is reminded of the classic story of Galileo, whose observations of craters and mountains on the moon contradicted the Church's Aristotelean view that it should be a perfect sphere. Thus, it was claimed that the moon was indeed still a perfect sphere, and that it merely had some invisible substance filling in the irregularities. Galileo, in his wit, replied that the invisible substance actually followed the contours of the visible surface. One could make similar counterarguments regarding the shields that are assumed to exist for no reason. ("The shield was down so all the ships invisible from our observation point could try to evacuate", or "the shield was so big it actually encompassed the Death Star, making it unfortunately useless", or "it was a holographic shield that only made it look like Alderaan was destroyed, but they had trouble and can't bring it down, and are thus trapped inside it", et cetera. Once one begins assuming (and assuming the invisibility of) what one seeks to prove, anything becomes possible.)
Beyond the philosophical matters regarding the type of argument, though, there are practical considerations. The assumed shield was so completely invisible in every way that it didn't have any observable effect on the superlaser whatsoever, which acted precisely as if it wasn't there. If it is invisible and does not interact with its surroundings in any way, it doesn't exist.
6. It has been suggested that the entire globe gets brighter as soon as the superlaser hits (i.e. not just the point of impact), and that this must mean there was a shield.
I originally didn't think the objection above was accurate in regards to the global brightening. The image below, for example, shows the left hemisphere from Alderaan both before the superlaser hits, and when it has just struck. Placed side-by-side, I can see no difference on the planet, though the space around the planet is ever so slightly brighter in the image on the right.
However, a difference does exist when closer scrutiny of RGB values is applied. I chose to test this further, because the .jpg compression scheme can produce significant variations in the red, green, and blue values of a regular image.
For instance, the image to the left was created using filled in areas of the exact same color, as part of the defense against another peculiar claim. Saved as a .jpg, however, there are readable variations. The middle blue area, for example, shows the following:
Position 38,10 (rough center) - 124, 153, 185 Position 28,10 (10px leftward)- 135, 155, 190 Position 48,10 (10px right)- 132, 148, 182 Position 27,19 (lower left corner)- 125, 143, 179
The total spread of each value is R:11, G:12, B:11
. . . and that's from saving an area of one color. For reference, the
darker blue area has a spread from 51,65,110 to 64,71,115, or R:13,G:6,B:5, and
the black line between the two (originally 0,0,0) reads 2,17,56!
Now, to test this in reference to Alderaan, let's aim for roughly the same points on two different screencap versions. The first is the "Ald" series, such as Ald00.jpg as used on this page. There's also Wong's "AlderaanBlast" series, used in the Wong debate. Let's compare similar spots on the images:
|AlderaanBlast-0 and 1, location
127,202: (a point in the area marked)
Ald00 and 01, location 95,154: (approximately the same spot)
Both do indeed show some additional blue, about 15-20 points worth, with a tiny amount of extra green. While that could fall inside the .jpg compression parameters, the fact that it appears on images of such different quality suggests that it is a real effect that occurs on the frames. I'm sure that it would not be related to the general bright white action occurring further to the right.
Now the question becomes one of origin. If I simply brighten AlderaanBlast-0.jpg by 25%, then location 127,202 ends up with RGB of 104,135,248. That is a difference of R:21, G:27, B:50.
Note, if you will, how simply brightening the image doesn't explain the difference. AlderaanBlast-1 only got brighter in the blue part of the spectrum (indeed, the red part of the RGB value gets lower between the two scenes, albeit within the parameters of .jpg variability). The brightened image got brighter in all three, though a bit moreso in blue as a result of what was already there.
This blue-spectrum brightening is consistent with what one would expect from refracted rays coming from deep within the atmosphere (i.e. from the same thing causing the bluish coloration of the clouds, or the blue sky of more earthbound example). It is not consistent with energy radiating from a shield.
7. It's been suggested that since Alderaan's clouds did not burn off as the superlaser hit, then there must've been a shield.
In the case of Alderaan, the superlaser was not the light source as it travelled through the clouds . . . we would expect a simple greenish refraction if that were so, just as a red laser pen will make your breath's cloud red when it is cold. Or, at the energy levels the shield proponents ascribe to the superlaser, we would have to expect that instead of a brightened cloud, we would be seeing the entire atmosphere burning away in that area. What we see instead is a simple brightening of the cloud, and even though the areas beyond that central cloud featuring the largest amount of brightening are simply other clouds, the opposition declares them shield flares.
What is being claimed in the objection above is that the light did not burn off (i.e. vaporize, not literally set aflame) the clouds, which is true. (And, incidentally, I was the first to notice that.) This is taken to require the presence of a shield.
So does that mean there had to have been a shield? Not at all. If you've ever watched videos of nuclear tests (preferably the really big megaton-level bombs during a surface blast), you've seen that they burn off the nearby clouds . . . but not immediately. Even those clouds which are directly overhead will generally survive for several moments. As example I present an image of the 11 megaton Castle Romeo test from March 27, 1954, shortly before dawn . . . this both illustrates the concept of cloud burn-off, and that it is not instantaneous:
(with thanks to Carey Sublette's Nuclear Weapons Archive)
In the above, you can see that the fireball, which has had time to rise to high altitude, has only just begun to burn off the clouds above. Next, I present an image of the Castle Bravo test. This test, the largest US test ever, involved a 15 megaton detonation shortly before dawn:
The above image occurs a few minutes after the initial blast, at which point the fireball has only just cut a small hole into the clouds thousands of feet above the surface.
That said, however, it seems peculiar that even a 15 megaton bomb wouldn't burn off clouds at, say, 30,000 feet (9144m). If we were to simply apply the inverse square law, the energy at that range would be about 59 megajoules per square meter! How is it that the clouds, the visible parts of which are composed of ice crystals and tiny water droplets, weren't completely vaporized?
The answer is manifold. First, only some of a nuke's yield is radiant energy (i.e. visible light, et cetera). Large nuclear weapons in atmosphere only emit about half of their energy in that manner . . . the rest is radiation (such as neutrons) and blast effects. Second, of that fifty percent or so of radiant energy, most is in the upper UV and lower X-ray band, to which the atmosphere is almost entirely opaque. (High energy X-rays can form at first, and these can penetrate a great distance. However, they will be absorbed and re-emitted as lower-energy X-rays.) As a result, much of the radiant energy doesn't get very far, and instead heats the nearby air to intense temperatures. These temperatures, however, are still far less than what exists at the center of the detonation. And last but not least, there is the shockwave itself. Initially moving at some 30km/sec, it also heats the air, ionizing it and rendering it incandescent. Though itself glowing, this incandescent air is opaque in the visible spectrum, and thus temporarily blocks the far brighter outbound visible light from the detonation itself.
Therefore, instead of 59 megajoules per square meter hitting the clouds, we're left with a significant reduction of that value emerging over a greater amount of time, thanks to the nature of nuclear weapons plus the effects of the atmosphere between the clouds and the point of detonation. That is why there is no cloud burnoff at the higher cloud layers until the much cooler top of the mushroom cloud reaches the area.
Of course, a planet-killing beam is going to have a much greater energy than a mere 15 megatons.
The 1e38J energy of Alderaan's destruction, if it were all released at the point of impact, would be equivalent to a 2.39e22 megaton bomb. The inverse square law would suggest 9e28J per square meter at 30,000 feet. One can hardly see how the atmosphere could manage to contain that sort of yield even if it were nuclear in origin and even if the superlaser had left the clouds unaffected as it passed through. Carey Sublette puts it this way:
"The intensity of thermal radiation increases very rapidly - as the fourth power of the temperature. Thus at the 60-100 million degrees C of a nuclear explosion, which is some 10,000 times hotter than the surface of the sun, the brightness (per unit area) is some 10 quadrillion (10^16) times greater!"
That said, it would appear that the shield is necessary provided we assume that the superlaser was a 1e38J beam. Is that a valid assumption? Well, the rest of the Alderaan evidence is consistent with simple cloud illumination and contrary to the shield hypothesis, which means that even if we accepted this concept it would contradict the rest of the evidence.
Understand that the fact that the lack of cloud burn-off merely serves to prove that the superlaser did not impart sufficient energy to burn off the clouds as it passed through the atmosphere (or to simply start burning off the entire atmosphere altogether), and you're on your way toward properly understanding the Death Star superlaser. But, that's a story for another section.
There's been some confusion regarding the issues above, specifically in reference to the atmospheric brightening. Once again employing my utter lack of artistry, I shall try to clear those up a bit. First, let's look at a view of Alderaan from above, just a moment before the superlaser hits:
Yes, I know, it is utterly craptastic "art"work, but it is here to serve as illustration, not a model or close representation. Basically nothing is to scale with anything else, but this allows us to see the gist of what's going on more effectively. You can see the superlaser about to hit, the cloud bank below the beam, and there's a brightening off to the right that represents the sunlight hitting the planet. Two other clouds are visible, one in the sunlight and one in the shadow to the left.
So, let's skip forward to the first frame of impact. Here's what the shield proponents would say is going on:
Now, bear in mind, there are many opposing camps in the shield group. Some would not place the additional glow on the cloud and sky below . . . others would have the shield boundary inside the atmosphere. Since (a) I didn't want to spend the rest of my life making my crappy illustrations, and (b) the majority of the shield group seems to argue for something akin to the above, the above illustration is the one I made. There is supposedly a shield flare (or 'glow' or 'halo') where the superlaser hits the shield, and this brightness radiates outward. The most basic concept of the shield proponents is that the glow on the cloud is coming from above. The next frame would look something like this:
Now maybe the whole atmosphere would be brightened according to some camps, whereas others would have no atmospheric brightening at all. Others might refrain from including the bluish shield glow that others use to explain the blue brightening between the clouds. In any case, the parameter they all agree on is that the brightening is primarily shield-related, and that the brightening is most prevalent (i.e. almost exclusively) over the clouds of Alderaan, which are lit from above.
There are a wide variety of reasons to dispute the above and the variations of that, and these are presented on this page. The alternative to those is presented below:
The above, roughly (pardoning the crappy illustration), is what I think is going on. The superlaser punches through the atmosphere, strikes the surface, and the flash from the impact site illuminates the atmosphere in keeping with the refraction we would expect from such a bright flash in atmosphere. The glow that illuminates the central cloud comes from below. The far edges of the clouds are darker than the parts closer to the superlaser, but brighter overall.
There is no evidence for planetary shield technology in use at Alderaan, and the concept is contrary to what we observe. Further, given that Alderaan did not demonstrate a planetary shield (and that most of the objections actually serve to help disprove the concept of a planetary shield), it would seem, judging by Vader's comment, that there is no full-scale planetary shielding anywhere in the Empire. Theater shields could cover major cities, in theory, but that is as far as Imperial technology can carry us.
The screenshots of the Special Edition version were created from a vidcap provided by Mike Wong. The picture from the Original edition also originates with Wong. Special thanks go out to NASA, for making the lovely and helpful pictures of Earth. Special thanks also to Carey Sublette, author of the Nuclear Weapons Archive.