[net.misc] the moon

tmh@ihldt.UUCP (10/21/83)

It seems to me that back when I was getting my B.A. that it was
explained to me as an optical illusion similar to the one with
the two lines with arrows pointing in opposite directions.  The 
size determiner seems to be the average size house (i.e. thing
that interupts your horizon) in your neighborhood.  The story in
class went; some Anthropoplgists first noticed this when they were
with some Afican desert dwellers and were remarking on how big the
moon was.  The natives remarked that they were crazy since the
moon never changed size.  The natives lived in small huts and
there were virtually no interuptions on the horizon.

				It just go to show that to 
				people who live in grass huts
				the moon is a harsh mistress?!?,
					Tom Harris

rob@lzmi.UUCP (10/21/83)

I believe the reason the moon appears larger when it is closer
to the horizon is that at that angle, there is more atmosphere
between you and the moon, which acts as a sort of magnifying glass.
(similar to the way a pencil in a glass of water appears distorted...)

...........rob

walsh@ihuxi.UUCP (10/24/83)

Sorry Rob, no way. If you look at photos of the moon in time lapse from
horizon to zenith, it is exactly the same size in each photo. The reason is,
as I and a few other people have explained, the reference to the horizon
creates an optical illusion (i.e., the moon next to a tree looks much larger
than it looks when overhead). The difference between the atmosphere at the
horizon and the atmosphere overhead is not sufficient enough to bend light
to that degree.

mmt@dciem.UUCP (Martin Taylor) (10/24/83)

The Moon Illusion has a venerable history, with theories going back to Plato.
Some of what has been written to the net is now accepted as giving part
of the illusion, but the atmospheric idea isn't one of them. The effect
of the atmosphere is to squash the shape top to bottom into an ellipse,
not to magnify it in any dimension. For a partial discussion, see Scientific
American about 10 years ago (look in an index volume in the library). The
illusion has many parts, and I can't remember most of them.

Martin Taylor

eric@apollo.UUCP (Eric Peters) (10/25/83)

As to why the moon looks bigger when it's near the horizon; it can't be simple
atmospheric distortion:

   1) When I take a picture of the moon near the horizon, it doesn't look bigger
      than normal in the resulting picture (I measured it); and
   2) When I see the risen moon just over a hill (i.e. at an angle above the
      horizon where it usually doesn't look bigger) then it DOES look bigger.

Could it be a subjective effect, similar to the sky appearing to be a flattened
dome?  (Ask someone to point at a place in the sky halfway between zenith and
horizon, and they will usually point up at about a thirty degree angle!)

                                                                  Eric