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Re: (meteorobs) Constellation Distortions/Meteor Plotting

In a message dated 12/11/01 8:45:09 PM Eastern Standard Time, 
unclefireballmtf@yahoo.com writes:

<< It is quite apparent with what I have seen while
 meteor hunting that the two bright stars in Gemini:
 Pollux and Caster, appear to be spread farther apart
 than the listed 5 degrees, when low above the horizon.
 At that height they appear more like 7 or 8-deg apart.
 Once the constellation has risen a good distance from
 the horizon and towards the zenith, however, the stars
 become more or less what a rough 5 degrees should look
 like.  With that said, about how large of distortion
 occurs with the constellations low in the sky and/or
 is there supposed to be any? 
  >>
From the classic book:  "The Stars/A New Way to See Them" by Hans A. Rey, 
page 70 (softcover version):

A FEW THINGS TO BE AWARE OF:  Sun and Moon look much larger near the 
horizon than when they are high up (the so-called Moon Illusion), and the 
same is true of the constellations.  They seem to shrink as they rise.  Just 
watch, say, Cassiopeia at nightfall in August, low in the sky:  it looks 
quite large; at midnight, about halfway up in the sky, it will look smaller, 
and even smaller before dawn when it is almost overhead.  By the same token, 
stars in the lower part of the sky seem higher up than the actually turn out 
to be if we measure their height or altitude.  The Pole Star, e.g., wich at 
latitude 40 degrees is about 40 degrees to the horizon (which means 10 
degrees closer to the horizon than the zenith), seems to be at least halfway 
up in the sky.

Rey adds a footnote concerning the Moon Illusion:  It actually is an 
illusion.  When measured or photographed the moon has exactly the same size, 
whether high or low in the sky.  We have more experience in judging the size 
of objects (an acquired ability) when looking ahead than looking straight up, 
and things seen high overhead (not only the moon) look smaller to us than 
when seen at the same distance horizontally.

-- joe rao
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