The Earth Is Not Flat
OCT 25, 2010
A few summers ago I took the picture shown at right of a sunset over
Lake Michigan. Unlike the oceans, Lake Michigan has no surf and when
there is no wind, the surface can be very smooth as it was on the day I
took this photo. Later when I looked at the photo I noticed that the
upside-down reflected image of the Sun on the water looked slightly compressed
relative to the Sun itself. At first this made no sense to me. Then,
in an "Aha!" moment, I realized it is compressed because the Earth is
not flat and therefore the surface of Lake Michigan is not flat.
Thinking of the surface as slightly curved nicely explains the
compression of the reflected image. I sat down and worked out the
trigonometry and amazingly I was able to compute the diameter of the
Earth just from measurements taken off from this picture and an estimate
of how high I was standing above lake level when I took this photo.