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Astronomers using one of the world's largest telescopes captured the brilliant explosion as the Kaguya spacecraft slammed into the Moon. Jeremy Bailey and colleague Steve Lee used the 3.9-metre (153-inch) Anglo-Australian Telescope in New South Wales to record a bright flash marking the impact of the Japan space agency JAXA's robotic probe. The crash, at around 4.25am local time today in New South Wales, happened on the unlit, dark side of the Moon , close to the edge of the side illuminated by sunlight, called the terminator.
NASA is due to launch a new unmanned probe next Wednesday that will fire a missile into a crater near the Moon's south pole in October.
On Earth, the interaction with the surrounding matter, be it air, water, or whatever, means that the initial energy is very quickly, in a few milliseconds, spread out over a fairly large amount of matter, no matter what the nature of the explosive. This material, typically air, forms a luminous fireball that expands at the speed of sound in the air that has been heated by the explosion, which is faster than the speed of sound in ordinary cool air. The result is a shock wave at the surface of the fireball. As the fireball expands it compresses and heats the surrounding air, while losing energy by radiation and also because of the work it is doing on the outside air, all of which causes it to cool. Eventually it cools to the point where it is no longer luminous, the shock wave moves out ahead and makes the BANG! that we hear and that may knock down buildings, and a cloud of swirling debris, smoke, and maybe brownish nitrogen oxides are left behind.
In space, the first few milliseconds proceed as they would in air (say), but then the transfer of energy to the surrounding air never takes place. As a result the initial small, intensely hot fireball simply keeps expanding at very high speed, and the expanding gases and any fragments fly off in straight lines. The fireball cools by radiation at first, but as its density drops it becomes so transparent that radiation is suppressed. For a chemical high explosive, the expansion speed would be a few thousand feet per second. So for a moderate size explosive -- say 1 meter across -- the products will expand to 100 meters in probably less than 0.1 sec, meaning the density will have decreased by a factor of a million, and the visible explosion will effectively be over. Visually the effect would be of a very brief, brilliant flash in a region only a little bigger than the actual extent of the explosive material. Of course there would be no billowing swirling smoke, and any fragments would almost certainly be moving too fast to be visible. The effect would probably be something like that of a big flashbulb.
For a nuclear explosion, the fireball would radiate mainly in the x-ray and ultraviolet, which are not visible to the eye, although the visible part of the radiation would produce a blue-white flash. The expansion speed would be many hundreds or thousands of times faster than for a chemical explosion, so that the time scale would be less than a millisecond. All the material near the source would be vaporized, so there would be no fragments. If the explosion was truly in space, and not in a tenuous atmosphere, then viewed from a survivable distance the effect would probably be similar to, but even less spectacular than, a chemical explosion.
There is one account of a nuclear explosion in the public literature that I know, that of the 1 Megaton "Starfish" explosion in 1962 over Johnston Is. in the South Pacific. Because it was not really in space, but in the upper atmosphere a few hundred km high, it created a ghostly fireball hundreds of km in extent, much less brilliant than in air, but still "a fearsome sight" (according to Bernard J. O'Keefe, "Nuclear Hostages", 1983).
Originally posted by watchZEITGEISTnow
Why crash it? Maybe this is a strike at the inhabitants of the moon?
Originally posted by watchZEITGEISTnow
Worlds most powerful telescope captures images that look like something off a mobile phone would see, should be the headline.
...why build a craft that cannot be returned to our planet? Why crash it?
why not just set it for a infinite course into infinite space?