Maybe some of you will remember a rather complete booklet by Gianni Ferrari
on how to determine wall azimuths by many methods... like the one of the
corner shadow.
Well, this method is very simple but not so much accurate as one could
imagine.
There are two main sources of error or inaccuracy:
* The most important one is that one can't determine precisely when the Sun
crosses the wall's plane: shadows are fuzzy because of the Sun's finite
angular
size.
* Second you have to consider errors on the wall: certainly walls have
bumps, the wall's
edge to the ground is unreliable, walls are not completely vertical, and
so on.
However, you can get a better precision with the same method using a
tripod, a small
spyglass (or something like this) and a brilliant circumpolar star (or
better yet
a couple of them like the Big Dipper's pointers). If you know its Right
Ascension,
and the sidereal time when it crosses your wall's plane you can
calculate its
declination in the same way.
Best regards,
Anselmo
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