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Re: Private Universe and the Seasons



On Sun, 21 Sep 2003 22:25:31 -0400 Chuck Britton <britton@NCSSM.EDU>
writes:
Hugh - or maybe someone else -- mentioned both umbra and penumbra
cones. One converges and the other diverges. For a finite sized sun
including rays not totally radial or totally parallel - won't BOTH
of these produce a pinhole 'image'.

Perhaps it would be better if you rephrase your question.
Although the penumbra always diverges, the umbra does both.
It converges to a point and then it diverges.
In any case a pinhole image will be formed and
it can be recorded with a pinhole camera.

Herb


---------------------- ----------------- -------------->
At 7:42 PM -0400 9/21/03, Bob LaMontagne wrote:

Hugh Haskell wrote:



Doesn't the size of the spot from a pinhole camera depend on how
far
away from the aperture you place the receiver? I would guess
that the
clearest image would occur somewhere near the point where the
"umbral" rays cross. If you take the image size at that point to
be
the diameter of the penumbra, it will necessarily be larger than
the
aperture in the case where the rays are slightly converging, as
they
are from the sun.


The pinhole spot, as well as the image from any lens used, subtends
1/2
degree, same as the sun itself. As you get further from the
pinhole, or
use a longer focal length lens, the image gets larger, but still
subtends 1/2 degree.

Bob at PC


--
Chuck Britton Education is what is
left when
britton@ncssm.edu you have forgotten
everything
North Carolina School of Science & Math you learned in
school.
(919) 416-2762 Albert Einstein,
1936




Herb Gottlieb from New York City
A nice friendly place to live and visit