Next message: Trevor J. Kenchington: "Re: Voyaging the traditional way"
Alex E wrote:
"I am not speaking of eclipses which are rare events. One method was already
discussed: timing the occultations of stars by the dark edge of the moon, a
method slightly less precise than that of lunar distances because the distance
is too small, and only available for somewhat less than 1/2 of each month, when
the moon moves with its dark edge forwardis:-)"
Maybe we should experiment. How many occultations can you observe during the
next couple of months? By the way, if you're excluding sextants, should you
also exclude binoculars, or do we permit them? And you may be able to get away
with using the period when the Moon is moving with dark edge trailing, too. An
attentive observer can time emmersions almost as well as immersions.
And:
"Another method was proposed by Bill in our recent off-the-list conversation:
timing the rise and set of various bodies. Each such timing gives you one
position line. It is interesting, how precise can this method be. (I understand
that the major obstacle here is refraction)."
How much error are you guessing based on variable refraction? You should
probably expect errors of as much as 15 arcminutes on a regular basis (not bad,
not great). It's important to remember, too, that you can't see any celestial
objects at the horizon except the Sun and the Moon. Atmospheric extinction is
typically 11 or 12 magnitudes right at the horizon so you will NEVER see a star
or planet rise or set without optical aid.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
