NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How Many Chronometers?
From: George Huxtable
Date: 2009 May 7, 10:51 +0100
From: George Huxtable
Date: 2009 May 7, 10:51 +0100
Henry Halboth gave his view, with good sense as usual- "Astronomical observations with a reliable, error free or error corrected, sextant, quintant, or even octant can be remarkably accurate as respects the determination of Chronometer Error, even on a good sea horizon. In my personal experience, I believe the Lunar Distance to be the more difficult observation as it probably requires the greater obsevational ability, but both the Equal Altitudes and Time Sight solutions are well within the capability of the average observer and will produce satisfactory results on a good sea horizon ..." However, he didn't point out, this time, as he had done in a previous message, that though the equal-altitude or time-sight operations can be inherently precise, they can only work if the longitude is well known, such as off a well-identified headland. Lunar distance, however, can be used to determine chronometer error at the time you might need it most badly, before sighting land. The problem is that the observation needs to be made so damn precisely. An error of 1' in the lunar distance itself can give rise to an error of 2 minutes in the chronometer time, or about 30' in the resulting longitude. So it provides a rough-and-ready answer, which may help to avoid disaster but not a precise correction to the chronometer. It's nowhere-near good enough to allow a new rate to be deduced. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---