Re: Private Universe and the Seasons

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

On Friday, Sep 19, 2003, at 09:07 US/Pacific, Jim Green asked:

> In the midst of this discussion could someone please tell me
> what a "Sun ray" is.  Is it rerally helpful to talk about such things?

A sun run is an extremely useful concept in geometrical optics.
It is a direction along which electromagnetic waves are moving
in a particular location. It is the direction of the Poynting vector,
I  suppose. But I do not tell this to students when they start
learning optics. To them it is introduced as a direction along
which light is propagating. What is wrong with this kind of
traditional modeling? Yes, it is like the caloric model of that
thing (am I allowed to name it?). We have to start teaching in
simple ways. Then some students become ready for more
sophisticated descriptions.
Ludwik Kowalski