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In support (I think) of Marc's point, it might help to appreciate that
1) rays starting at DIFFERENT PLACES on the Sun and ending at a
SINGLE POINT on Earth are parallel to within ~30 minutes of arc.
2) rays starting at a SINGLE POINT on the Sun and ending at DIFFERENT
PLACES on Earth are parallel to within ~0.3 minutes of arc.
The difference is entirely explained by the fact that the Sun is ~100
times as large as Earth.
Marc Kossover wrote:
Howdy-
So, I am confused. Are most people arguing that the rays (whatever
they
are) from the sun that hit the earth parallel (to a good
approximation) or
not? I don't know where most people lie, but I'll give my answer.
I vote for not.
First, essentially parallel rays that go through a convex lens are
focused
to a very small point. This does not occur with any lenses that I
posses.
All of my lenses focus sunlight to an image that is a disk whose size
varies appropriately with the power of the lens.
Second, essentially parallel rays that go through a pinhole (large
enough
to ignore diffraction) creates spots approximately the same size as
the
hole. My pinholes cameras make patterns of light of the sun that vary
in
size, and in fact do a pretty good job measuring the size of the sun
if
you know the distance or vice versa.
Although the sun is very far away, it is also very large.
Marc "Zeke" Kossover
The Hockaday School
--
John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm