Re: Moon Illusion

[Joel Rauber <Joel_Rauber@SDSTATE.EDU>]

Here is my understanding of the moon illusion.  It is often  noted by folks
who look at the sky at night that the moon appears larger when it is near
the horizon (often oranger as well, but that's the other topic of
discussion) than it does when it is high in the sky.  Often this is
explained as being some sort of a magnifying affect attributed to the
longer
path length in denser atomsphere.  The correct explanation is that the
larger appearance is really an optical illusion and is not a true
magnifying
affect to any significant degree.

The size appearance is strongly affected by the presence of other close by
visual clues.  E.g. near the horizion the moon may be near a tree and the
eye/brain can compare the sizes.  But high in the sky there typically
aren't
such visual clues.  The trick that Leigh mentioned or the one I mentioned
are ways to occlude such visual clues.  If you do these tricks when the
moon
in near the horizon, the visual appearance of the size of the moon will be
remarkably reduced and the moon will appear much closer to having the same
size that it has when high in the sky.

Joel Rauber
Joel_Rauber@sdstate.edu


> -----Original Message-----
> From: phys-l@lists.nau.edu: Forum for Physics Educators
> [mailto:PHYS-L@lists.nau.edu]
> Sent: Thursday, August 31, 2000 5:28 PM
> To: PHYS-L@lists.nau.edu
> Subject: Re: Moon IllusionRE: The color of snow
>
>
>
> OK, so what is this famous moon illusion?
>
> Joel Rauber wrote:
>
> > > It goes away for me if I view it upside down by looking
> > > between my legs, the same technique that makes the Moon illusion
> > > go away.
> >
> > An easier way to make the moon illusion go away, is to take
> your thumb
> and
> > pointing finger and make the OK gesture so that you have a
> circle of two
> > digits and look through it at the moon.  I usually hold the
> tip of the
> > pointing finger about at the thumb joint.
> >
> > Joel Rauber
> > Joel_Rauber@sdstate.edu
>
> --
> Cliff Parker
>
> Never express yourself more clearly than you can think.  --
> Niels Bohr