Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Moon Illusion



I'll add a note to Joel's on the Moon illusion. The Moon actually
appears smaller when near the horizon than it does when overhead,
all other factors being the same. The apparent size of the Moon
actually varies by quite a lot over the month and year because
the Moon's distance from earth varies a lot (of the order of ten
percent, if my memory is correct).

The effects of altiude that I can think of are two. The Moon is,
on average, about 6,000 km farther away when it is near the
horizon than it is when overhead. This is a small effect, of
course, which should make it look about two percent smaller on
the horizon. Refraction also squashes the vertical dimension of
the apparent Moon when it is near the horizon.

This is all on top of a much stronger effect which is entirely
psychological, as Joel pointed out.

Leigh