Xref: utzoo sci.space:4250 sci.crypt:752
Path: utzoo!linus!philabs!prls!pyramid!oliveb!ames!umd5!purdue!i.cc.purdue.edu!j.cc.purdue.edu!pur-ee!pur-phy!clt
From: clt@pur-phy (Carrick Talmadge)
Newsgroups: sci.space,sci.crypt
Subject: Re: satellites
Keywords: resolution
Message-ID: <972@pur-phy>
Date: 15 Jan 88 23:39:33 GMT
References: <1988Jan12.180815.685@sq.uucp>
Organization: Purdue Univ. Physics Dept., W. Lafayette, IN
Lines: 32

In article <1988Jan12.180815.685@sq.uucp> msb@sq.UUCP (Mark Brader) writes:
>> A telescope at sea level, in perfect 
>> weather, is typically limited to no better than 1" (that is a unit 
>> of angle: 1 arc-second, not 1 inch).
>
>Probably it would be considerably better, since the atmosphere is at
>the right end of the light path.

Mark is right here.  This is a point which I screwed up on last fall
when this question was last discussed:  You'll do a lot better looking
in from the outside than 1 arc-second.  Numbers that were floating
around at that point were maximum resolutions of about 3-4 cm.

>However, diffraction is still a limit,
>as you say.  They might not be using visible light; how many times the
>frequency of violet light must you go to before viewing becomes impossible?

Depends.  Violet light is usually classified to be around 4200
angstroms.  The transmission coefficient of the atmosphere plummets
somewhere between 2900-3000 angstroms (at 2900 angstroms, it is less
than 1e-6) [Ref: International Critical Tables, Vol. V, page 268].
Over Antartica, with the hole in the ozone layer, you'll probably do
better, though. :-)  Anyway, you'll gain *maybe* a factor of two by
going as far as is practical into the ultraviolet.

Carrick Talmadge			 clt@newton.physics.purdue.edu
--------

    When you have eliminated the impossible, whatever remains,
    no matter how improbable, must be the truth. -- Sherlock Holmes

    Yes, but what happens if nothing's left? -- Watson's reply