NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: CelNav without sextant
From: Frank Reed CT
Date: 2004 Nov 2, 20:40 EST
From: Frank Reed CT
Date: 2004 Nov 2, 20:40 EST
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
"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
