Re: Private Universe and the Seasons

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

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