On Tue, 22 Jul 2003 18:39:21 GMT, "Mick" wrote:

Am I missing something? Is my arithmetic off? Presently Mars is some 20 arc
seconds wide. This implies that at 100 X's magnification, it should be 2000
arc seconds across...or just over 1/2 a degree, which is the diameter of a
full moon!! (1/2 degree = 1800"). Last night, the image at 100 x's is no
where near the size of a full moon. What am I missing here??

You were missing a full moon near the same line of sight ;-)

During one of my recent Mars observations (using a refractor without a
star diagonal) I couldn't help but notice how *small* (and bright!)
the moon was compared to my telescopic view of Mars. The scope's
magnification was between 200 and 300x.

Without the moon near the same line of sight it's *very* difficult to
accurately judge which would appear to be larger -- assuming you don't
"cheat" and use a little math!

An absent full moon isn't as large as most of our memories of it ;-)

Bill Greer