Lunar Illusion



The illusion of the moon being larger, when close to the horizon, is
well-known and well-documented. Explanations are varied and range from
a page or so of text to entire books. Ptolemy's explanation of the
illusion was that there is a frame of reference near the ground and not
in the sky. This explanation is generally held to be the most likely.

The illusion does NOT occur if you close one eye, and also does NOT
occur when using a conventional modern camera.

This, however, does NOT answer the question of whether the effect
exists when using a stereoscopic camera. These have existed since
Victorian times, so somebody has presumably taken a picture of this
kind. Does anyone know whether the illusion shows up in this case?

If it does not, then Ptolemy is presumably correct, as the illusion
cannot be reproduced mechanically. On the other hand, if it DOES show
up on a stereoscopic photograph, then the illusion must presumably have
a mechanical component and not be purely a product of the brain's
interpretation.

On a side-note, does anyone know of any good stereoscopic Hubble
images, where the same object has been viewed from the furthest extent
of the orbit? It would be interesting to get a better "feel" for
astronomical phenomena, by being able to get a better sense of the real
shape, as opposed to a flat projection.

.



Relevant Pages