NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars: Three simultaneous observations
From: Frank Reed CT
Date: 2004 Sep 23, 20:03 EDT
From: Frank Reed CT
Date: 2004 Sep 23, 20:03 EDT
Regarding Cook's lunars, Fred H asked:
"Please supply some numbers and details! Less than 1' of arc? Less
than 20"? Were these shore-based lunars? Did they use a sextant
stand?"
In samples I've checked the lunars are good to something on the order of 20" (it's hard to be more accurate because they were usually given with eyeball estimates of distance and direction to identifiable points of land). Cook on the Endeavour had the good fortune of having aboard an actual astronomer, Charles Green. This was ostensibly an astronomical voyage to observe the transit of Venus from Tahiti. Green used a hand-held sextant, aboard ship, to shoot most of the lunars. I don't know how many were shot on shore but the sextant was valuable and it may be that they never took it ashore. Cook also shot lunars, and it seems that Green taught some of the other officers to do them, though they apparently found his insistence on getting longitude in mid-ocean (when it was clearly un-necessary, from their point of view) rather annoying.
If you would like to explore this further, the post-voyage edited version of Cook's log has been e-published as part of Project Gutenberg. I don't have the URL handy, but you can search for it easily enough. When you get to the Gutenberg site, search on "James Cook" as author. After downloading the file, search for "moon" and you will be taken to sections on lunars.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"Please supply some numbers and details! Less than 1' of arc? Less
than 20"? Were these shore-based lunars? Did they use a sextant
stand?"
In samples I've checked the lunars are good to something on the order of 20" (it's hard to be more accurate because they were usually given with eyeball estimates of distance and direction to identifiable points of land). Cook on the Endeavour had the good fortune of having aboard an actual astronomer, Charles Green. This was ostensibly an astronomical voyage to observe the transit of Venus from Tahiti. Green used a hand-held sextant, aboard ship, to shoot most of the lunars. I don't know how many were shot on shore but the sextant was valuable and it may be that they never took it ashore. Cook also shot lunars, and it seems that Green taught some of the other officers to do them, though they apparently found his insistence on getting longitude in mid-ocean (when it was clearly un-necessary, from their point of view) rather annoying.
If you would like to explore this further, the post-voyage edited version of Cook's log has been e-published as part of Project Gutenberg. I don't have the URL handy, but you can search for it easily enough. When you get to the Gutenberg site, search on "James Cook" as author. After downloading the file, search for "moon" and you will be taken to sections on lunars.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
