Dear Tom,
Why do the sun and moon look larger as they rise and set and are close to the
ground?
Barry Baxter, Ottawa, Ill.
Dear Barry,
Both the sun and moon seem to be larger when they are positioned near the horizon,
but it is entirely an illusion.
It's such a compelling illusion, though, that it has a name: the "moon illusion."
No single explanation sufficiently accounts for the illusion, but it probably results
from the varying ways our minds relate the size and distance of the sun and moon
when they are viewed by themselves (high in the sky) or against a backdrop of other
objects (near the horizon). The sky at the horizon seems more distant than the sky
overhead. When viewed against the "more distant" horizon sky, the sun and moon
appear larger than when seen against the "closer" overhead sky.
