Moon Size Activities
I teach 6th grade science. What is a clear way to explain
to students why the moon appears to be different sizes when viewed
from Earth? Is there a fun way to model this for kids as well?
Check out the web site
for a very nice discussion of the moon size illusion.
It is not clear whether this refers to the "phases" of the moon, or to the
apparent size difference of the moon close to the horizon compared to its
apparent size when overhead. There are many demonstrations illustrating the
phases of the moon on various websites. Search the term: "phases of the moon
demonstrations" and take your pick. The apparent size difference of the moon
at various locations in the sky is trickier, but more interesting because
the result is counter intuitive. First, the effect is greater when the moon
is full, or almost full. Its apparently larger size when it is near the
horizon is an optical illusion. This can be demonstrated by taking a
photograph of the moon near the horizon using a modest telephoto lens on the
camera -- a 10X zoom on a digital camera should work well. Then repeat the
experiment at the same settings when the moon is high in the sky. Processing
the images -- say using computer digital imaging software -- will reveal
that the size of the disk is the same in both positions. This effect is
discussed in detail on any number of websites on lunar effects.
Although the Moon does vary in size from perigee to apogee (closest and
farthest points to Earth in the Moon;'s orbit) I am not sure of how to
illustrate this to children. While it is very hard to see the change in
the size of the Moon as it moves round Earth, the change is obvious during
solar eclipses. In an annular eclipse the Moon, at apogee, is smaller
than the apparent diameter of the Sun and we see an annular or "ring"
eclipse. Near perigee, the Moon is bigger and we see a total eclipse.
I looked up "Moon sizes demonstration" on Google and got some interesting
results. Best of luck!
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Update: June 2012