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Lunar and Earth Curvature of Horizon
Name: Annie
Status: other
Grade: other
Location: NV
Country: N/A
Date: 1/25/2006
Question:
Why is the curvature of the horizon on the moon so
obvious? I do not understand how since you cannot really make out
much with your eyes or a sophisticated camera past 2 city blocks.
Replies:
Annie,
There are several possible reasons why the curvature of the Earth is
not as easily observable as opposed to pictures you have seen taken
by astronauts on the Moon. (1) Since the average diameter of the
moon is 3,500km as opposed to the Earth's which is 6,400km (nearly
double) - then the curvature is not so pronounced. (2) Depending on
where you are there are many intervening structures, fog, dust,
trees, buildings (etc) that break up your view of the Earth's
horizon - if you were to stand on a boat in the middle of the ocean,
or on a particularly flat and featureless land (like where I live in
South-East Texas), you can readily see the Earth's curvature.
Greg (Roberto Gregorius)
Annie,
To keep the answer as simple as possible, the curature of the moon's
horizon is so noticable because its diameter is quite small. To
make an analogy to a two-dimentional object, think of a pizza. As
you cut slices it is easy to see that the crust is round. But
imagine that you made a pizza larger than the Earth. Now when you
cut the pizza, the crust would be so large, that it would be very
difficult for you to tell if the crust was round or not.
To put the answer in terms of math, think of the pizza as a
geometric shape--an isocelese triangle, with the base curved instead
of straight. Now, the tip of the pizza (the tip being the point
that was in the center of the pizza) makes an angle with the two
long sides of the pizza. If that angle is held constant and the
diameter of the pizza is increased (let us say from a 10" pizza to
an 18" pizza), the length of the crust is increased. As the crust
gets longer and longer it also has to become less curved in order to
keep the angle at the tip the same! So back to the moon and the
Earth, since the moon is so much smaller than the Earth, it is much
easier to see its curvature since it IS more curved than the Earth!
Matthew Voss
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Update: June 2012
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