NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Latitude by Spica
From: Frank Reed CT
Date: 2004 Jan 12, 04:00 EST
From: Frank Reed CT
Date: 2004 Jan 12, 04:00 EST
K. Kelly wrote:
"Hate to disagree but the use of Meridian Passage of stars to determine
latitude was very common in land based exploration."
Don't worry --you're not disagreeing. Land-based surveying had its own needs and preferences. I am under the impression that "Navigation-L" is mostly about navigation at sea. Not that land surverying is irrelevant (it isn't) but it's a different animal. At sea, observing altitudes of stars was apparently a rare practice.
You described some of A.Gregory's reasons for prefering star sights:
"1) It was more accurate
2) It removed the need for a lengthy noon time halt
3) It reduced the need to unpack equipment during the day then re-pack it.
4) It reduced the possibility of native attack during the noon halt."
Regarding point 1, there is no reason why star sights for latitude should be more accurate than sun sights (except that you have more star transits available in principle and you could average them, but that doesn't work at sea). Points 2-4 (especially 4!) don't matter at sea, but they're interesting issues for land surveying.
And you wrote:
"I think the technique was also more commonly accepted in those days than
you think. My copies of Raper (1849) and Norie (1852) both contain clear
exposition of "Lat by Mer Passage of a star" and appear to give it equal
weight to latitude by meridian passage of the sun.
That's actually why I posted this logbook evidence. MANY readers in the year 2004 make the huge mistake of believing that Norie, Bowditch, etc. describe the *practice* of navigation. They do not. Although Bowditch and Norie and others recommended shooting stars, navigators at sea rarely did so. Equal time in a navigation manual does NOT imply equal time at sea!
Now of course, I am describing the evidence from the logbook collections that I personally have seen. These are logbooks from American commercial vessels. Do you have evidence from other vessels? Not just suppositions based on recommendations in Norie... but real evidence. That would be fascinating.
KK concluded:
"I don't think we should fall into the trap of believing that sailors were the only ones to hoist a sextant in the Nineteenth century."
I don't think anyone's doing that. But 19th century land-based astronomy is a very different subject, I would say.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"Hate to disagree but the use of Meridian Passage of stars to determine
latitude was very common in land based exploration."
Don't worry --you're not disagreeing. Land-based surveying had its own needs and preferences. I am under the impression that "Navigation-L" is mostly about navigation at sea. Not that land surverying is irrelevant (it isn't) but it's a different animal. At sea, observing altitudes of stars was apparently a rare practice.
You described some of A.Gregory's reasons for prefering star sights:
"1) It was more accurate
2) It removed the need for a lengthy noon time halt
3) It reduced the need to unpack equipment during the day then re-pack it.
4) It reduced the possibility of native attack during the noon halt."
Regarding point 1, there is no reason why star sights for latitude should be more accurate than sun sights (except that you have more star transits available in principle and you could average them, but that doesn't work at sea). Points 2-4 (especially 4!) don't matter at sea, but they're interesting issues for land surveying.
And you wrote:
"I think the technique was also more commonly accepted in those days than
you think. My copies of Raper (1849) and Norie (1852) both contain clear
exposition of "Lat by Mer Passage of a star" and appear to give it equal
weight to latitude by meridian passage of the sun.
That's actually why I posted this logbook evidence. MANY readers in the year 2004 make the huge mistake of believing that Norie, Bowditch, etc. describe the *practice* of navigation. They do not. Although Bowditch and Norie and others recommended shooting stars, navigators at sea rarely did so. Equal time in a navigation manual does NOT imply equal time at sea!
Now of course, I am describing the evidence from the logbook collections that I personally have seen. These are logbooks from American commercial vessels. Do you have evidence from other vessels? Not just suppositions based on recommendations in Norie... but real evidence. That would be fascinating.
KK concluded:
"I don't think we should fall into the trap of believing that sailors were the only ones to hoist a sextant in the Nineteenth century."
I don't think anyone's doing that. But 19th century land-based astronomy is a very different subject, I would say.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
