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: Earth's shadow



Ken Fox is probably right about what Hewitt is trying to say. But I
don't get the point. And besides, it is not literally true. If the
earth were the same size as the sun, then the earth's shadow would not
taper at all. If the earth were the same size as the moon, then the
earth's shadow would be just like the moon's shadow and would taper by
one moon diameter over the earth-moon distance. In reality, the size of
the earth is between the size of the sun and the moon, so the earth's
shadow doesn't have zero taper, but it doesn't taper as fast as the
moon's either. Therefore it does not shrink by as much as a lunar
diameter over the earth-moon distance.

I suppose Hewitt would say that the earth is much closer to the moon's
diameter than to the sun's diameter. But that still makes his argument
just handwaving rather than reality... And I don't see any good reason
for the handwaving. Why not just say that the earth's shadow cast upon
the moon is large enough to cover the whole surface of the moon (and
then some) whereas the moon's shadow cast upon the earth only covers a
small portion of the earth.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.