" Well, thats a bit much to imagine. I am speaking about 100 - 150
x's..at
200-300 Mars should appear large..

Hi Mick,

Perhaps with more specifics the situation can be clarified. I was
observing Mars at 280x when the moon was a few degrees away in the
sky. I was using a refractor without a star diagonal (an important
point, as this made it very easy to glance back and forth between Mars
in the telescope and the moon with the naked eye). The diameter of
Mars in the telescope appeared to be *several* times the diameter of
the naked eye moon. Getting even more specific, the naked eye moon
appeared to be less than one third the diameter of the telescopic
Mars.

A little bit of math would show that if Mars (at 280x) appeared to be
over 3 times the size of the naked eye moon, then Mars at 100x would
appear to be somewhat larger than the naked eye moon.

The two most likely reasons why you felt that Mars at 100x appeared to
be much smaller than the naked eye moon are (in order of probability):
1) You were unable to directly compare the telescopic view of Mars to
a naked eye view of the moon. 2) Your telescope/eyepiece combination
was yielding a magnification much less than 100x.

Your math was accurate in your original posting. A telescope at 100x
will show a Martian disk that is larger in apparent size than a naked
eye moon. If you make a direct comparison next month as I (more or
less accidentally) did this month you'll discover that the *tiny* disk
of Mars in a telescope at 100x is indeed larger than the apparent
naked eye diameter of the moon.

It's a *big* mistake to compare the real-time telescopic size of Mars
to the memory's naked eye size of the moon. It's far better to make
the comparison when both are in nearly the same line of sight, thus
allowing one to rapidly glance back and forth from one to the other.



Thanks Bill...it makes more sense now...but seriously, we look at the full
moon unaided and see significant
light and dark areas ie: "the man"...(I've always thought of it as a woeful
female myself) and presume that dark and light features on Mars will be
equally apparent...so far this is not the case under good seeing. What I
get is a faint speck of a south polar region and a "hint" of syrtis major at
20.5". My scope is exactly 100 X's with a 9mm OR.

..I find it hard to believe that my memory, or impression, of the unaided
full moon disc (within reason) is that affected by "illusion". I will have
to compare the two next month as you describe.