Among other things, sascha wrote:

> I was refering to another effect which makes objects appear blurry in a
> telescope. I'm not sure what causes this effect, but I think it is
> bacause the mirror (a paraboloid) will focus only parallel rays (the
> object to be viewed must be either a point or ininitely far away). A
> planet is neither of both, so not all the light from the planet will be
> focused an the same plane, resulting in a blurry image. It gets better
> if you use a larger mirror (I guess that's the reason why they use 8
> meter mirrors in the VLT :-)

The main reason for using large telescopes (with large mirrors) is they 
receive more light and so allow astronomers to study fainter and more 
distant objects.

-- 
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0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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