P3D Re: Moon Size...Stereogram

[Larry Berlin <lberlin@xxxxxxxxx>]

> Date: Fri, 14 Jan 2000 
> From: Tom Hubin <thubin@xxxxxxxxx>
> ........
> A friend sent me some info on the moon because I do some software on
> tides and tidal currents. One of the references includes an animated
> stereogram. Check it out.
> 
> http://www.research.ibm.com/news/detail/newmoon.html
> 
> Tom Hubin
> thubin@xxxxxxxxx
> 


Hi Folks,

First I want to congratulate Bob on getting the P3D system back up and
running!

I checked out the link (above) provided by Tom, and it is interesting,
but I can prove without any doubt that their stereogram illustration
DOES NOT PROVE THEIR POINT IN THE SLIGHTEST.

That does not say their information is wrong, though I strongly disagree
with their findings. I would have to look at their -real- information
first. 

I do agree that apparent distance does have an effect on our
perceptions, and they have done some interesting measurements (though
I'm extremely skeptical about how they made them). However it doesn't
appear that they have addressed the issue of the moon illusion, merely
provided an interesting set of side observations. 

'IF' there is any truth to their conclusions, the illustration provided
does -not- communicate that information. There are two reasons. One, is
that the stereogram appears to provide a smaller moon when the moon gets
closer, which is directly opposite their claims!!! (Duh...) Second, the
illusion present in the animated stereogram derives it's size change
from a completely different source. The distance from the observer to
the computer screen and the observing geometry of that local space. ALL
of the distances involved in watching a real moon rise above the horizon
are far more distant than a computer monitor. They have confused many
factors and totally ignored others to make their point.

Besides, there is a very real size difference between a horizon moon and
the elevated moon. The so called illusion may exist too, but it's not
the only factor by a long ways. Over many years of watching the full
moon rise above the horizon, I have watched the apparent size of the
moon change while there is still reference landscape easily within view. 

Not only that, if the moon rises above mountains relative to the viewer
in a valley (removing the low angle atmospherical effect), it does NOT
appear the same size as it does rising above a flat horizon despite
having landscape in the view for reference! This observation would
completely contradict their assumptions. The apparent size is affected
by refraction in the atmoshpere near the horizon (as well as by any
psychological effects). As the moon lifts above critical angles, it
reduces in apparent size due to significantly less refraction. Perhaps
their illusion only applies -after- the moon has lifted by that small
amount, compared to being fully in the sky? 

I applaud their attempt at documenting their theories, but they missed
it by a mile. Another thing they are wrong about, the horizon moon
appears significantly closer not more distant, if only because of it's
apparently larger size. What moon have they been watching anyway? Do
they understand anything at all about optical properties? Have they ever
watched a sunset? Have they ever observed a Green Flash at sunset? I
have. If you haven't heard about the green flash or what causes it, it's
described and illustrated somewhere in Scientific American within the
past 10 years. Maybe several articles. Refraction of the atmosphere
really does exist.

Later,
-- 
Larry Berlin

3D Webscapes
lberlin@xxxxxxxxx
http://3dzine.simplenet.com
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