Re: Private Universe and the Seasons

[Chuck Britton <britton@NCSSM.EDU>]

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'.


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