NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars: Jupiter's BIG.
From: Frank Reed CT
Date: 2003 Dec 24, 17:44 EST
From: Frank Reed CT
Date: 2003 Dec 24, 17:44 EST
Huxtable wrote:
"The point I am trying to make is that in order to RATE a chronometer,
rather than simply establish its error, one needs to find the rate AT OR
NEAR THAT MOMENT, not what it has been averaging over a previous passage."
That's the sort of point that a shorebound mathematician might well have made in the 19th century. But in practice, there's no significant practical advantage of knowing the instantaneous rate instead of the average rate over several months. Indeed, if the instantaneous rate is observed while the ship is at anchor and the chronometer is motionless, its rate may be very different from the rate at sea. The average rate determined by one observation of longitude (more likely from sighting land or speaking another ship than from a lunar) would provide solid practical information on the chronometer's rate.
And:
"The trouble with using a lunar to determine rate is that because each
measurement is so inaccurate (to a minute or two of time) then any
determination of rate over a short interval is hopelessly imprecise."
True, you could not get an instantaneous rate from lunars, but as noted above, that's of no consequence in practice. ONE lunar (combined with the known error a few months earlier when leaving port) can rate a chronometer in a fashion that has practical value for a navigator at sea.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"The point I am trying to make is that in order to RATE a chronometer,
rather than simply establish its error, one needs to find the rate AT OR
NEAR THAT MOMENT, not what it has been averaging over a previous passage."
That's the sort of point that a shorebound mathematician might well have made in the 19th century. But in practice, there's no significant practical advantage of knowing the instantaneous rate instead of the average rate over several months. Indeed, if the instantaneous rate is observed while the ship is at anchor and the chronometer is motionless, its rate may be very different from the rate at sea. The average rate determined by one observation of longitude (more likely from sighting land or speaking another ship than from a lunar) would provide solid practical information on the chronometer's rate.
And:
"The trouble with using a lunar to determine rate is that because each
measurement is so inaccurate (to a minute or two of time) then any
determination of rate over a short interval is hopelessly imprecise."
True, you could not get an instantaneous rate from lunars, but as noted above, that's of no consequence in practice. ONE lunar (combined with the known error a few months earlier when leaving port) can rate a chronometer in a fashion that has practical value for a navigator at sea.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
