Re: Jet lag without leaving home

Aaron Denney <wnoise@[EMAIL PROTECTED]
> wrote:
> I hadn't realize eccentricity and inclination made such a difference.
> (15 minutes difference between mean solar time and apparent solar
> time).  It's still only half that required to get an offset of an
> hour, as Jette described.  I'd expect mountains to make a more
> practical difference in many places.

Sunrise and sunset are defined in terms of when the direction to the
sun is horizontal, not in terms of when the sun is visible.  Otherwise
in a deep narrow canyon, sunrise might be at 1150 and sunset at 1210.
So mountains have a negligible effect on sunrise and sunset times.

If you chart where on Earth the sun is directly overhead each day at a
particular hour, you'll get a vast, slightly asymmetrical figure-eight
shaped figure called an analemma.

It would be a fun project for someone to spend a year walking the
analemma, i.e. arranging to always be in the place where the sun is
directly overheard at noon.  You'd have to walk pretty fast in March
and September, but I think it's doable.  This would have to be done
in Africa, since anywhere else large parts of the analemma would be
at sea.  I suspect it's not yet politically possible, as it would
require crossing too many borders controlled by tinpot dictators.
-- 
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html
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