NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robert H. van Gent
Date: 2019 Oct 11, 07:58 +0000
Hi,
Regarding your first question you may find these recent papers by Siebren van der Werf useful
https://journals.sagepub.com/doi/full/10.1177/0021828617705244
https://journals.sagepub.com/doi/full/10.1177/0021828619864472
Regarding your second question you could also add the mariner’s astrolabe as a possible observing instrument.
Rob van Gent
From: NavList@fer3.com <NavList@fer3.com>
On Behalf Of Doug MacPherson
Sent: Thu 10 October 2019 20:32
To: Gent, R.H. van (Rob) <R.H.vanGent@uu.nl>
Subject: [NavList] In the Wake of Magellan
Recently sailing in my armchair I was pondering the navigational challenges Magellan and other European sailors of his time must have experienced. (Early 16th century).
I assume that the sun was the primary source of information for determinig latitude and that they had some table showing them the declination of the sun over the course of the year.
Three questions came to mind:
1. Where did the sun's declination table come from? Did the Spanish, Portuguese or other governments supply it? How did they get it?
2. What tool were they using to determine the altitude of the sun at noon? A cross staff? kamal? backstaff? John Davis Did not invent his "Davis" quadrant (a backstaff) till 1594.
3. If, in an unfortunate accident, the declination table blew overboard, and our intrepid captain remembered that the sun's declination was about 23.45° South and North on December 21 and June 21 respectively, and 0° on March
21 and September 21, would a linear approximation of the sun's declination from that rememebered data be accurate enough to navigate with? What would be the max error from the sun's actual declination and when would that occur?
Finally, would the max error matter given the tools they were using?
Cheers,
Doug
38° 34.3' N
121° 28.5' W
