Subject:
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Re: Evolution of Earth and moon (was: Couldn't resist)
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Newsgroups:
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lugnet.space, lugnet.off-topic.geek
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Date:
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Mon, 16 Jul 2001 14:21:35 GMT
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Viewed:
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9377 times
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In lugnet.space, Ross Crawford writes:
> I think most of this sounds reasonable, but I'd guess that laser still
> follows the inverse square "law".
I thought that the whole point of a laser is that it doesn't - it's a
directed beam of parallel waves of light.
The inverse square law is for a diverging beam. As distance from the source
increases, the area the beam is spread over increases (with the square of
the distance), so that intensity at any one point is less (by an inverse
square). With a laser, the area it covers is constant, hence no loss of
intensity.
If you were to shine a small torch at someone across a football pitch, you
can imagine that they might notice you as the source, but it wouldn't
noticeably illuminate them because the light isn't intense enough. If you
shine a laser pointer though, they could see the spot of light on them,
regardless of the distance.
Now, lasers aren't perfect, and there may be some divergence over the
Earth-Moon distance. I guess this would have to be inverse-square related
then, but with a much narrower angle of divergence. Anyone know for sure?
Jason J Railton
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