NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Coordinates on Cook's maps
From: Alexandre Eremenko
Date: 2007 Apr 15, 10:40 -0700
From: Alexandre Eremenko
Date: 2007 Apr 15, 10:40 -0700
I used photocopies of the original maps of Cook's expedition published by Hakluyt Soc. by Cambridge University Press in 1955 (Available at Purdue library). There are 68 maps and shore views, and the collection is claimed to be complete. Only the following maps have the right scale and coordinates on the sides, with longitude from Greenwitch, to determine positions of certain points with 1' accuracy. I choose a conspicious point on a map, usually a cape, take its coordinates from the map, and then try to identify the same point on Terraserver photos. The results are rounded to 1 minute. First error is in latitude, second in longitude. First voyage (no chronometers were available): Chart 9. Cook's coords: 16d40'S 151d29'W Terraserver: 16d41'S 151d32'W Er:-1', -3' Chart 13. East Cape: 37d43'S 179d0'E, Terraserver: 37d41' 178d33' Er:+2', +27' Table Cape: 39d07' 178d25' Terraserver: 39d12' 178d00' Er:-5', +25' Chart 18. Cape Teerawitte: 42d21'S 175d35'E Terraserver: 41d18' 174d42' Er:+3', +53' Cape Campbel: 41d41' 175d13' Terraserver: 41d47' 174d20' Er:-6', +53' Chart 24. Cape York: 10d42'S 141d42'E Terraserver: 10d43' 142d36' Er:-1', -54' Second and third voyages (both chronometers and Lunars used): Chart 35. Friendly Islands: 21d16'S 174d44'E Terraserver: 21d17' 174d55' Er:-1', -11' Chart 55. N point Hawaii isl: 20d17'N 156d00'W Terraserver: 20d16' 155d52' Er:+1', +8' Karakakooa bay: 19d28'N 156d00' Terraserver: 19d28'N 155d56' Er:-0', +4' Chart 57. Aivatcvhka bay: 52d54'N 157d33'E Terraserver: 52d56' 158d28' Er:-2', -45' Another point there:52d51' 157d48' Second and third voyages (both chronometers and Lunars used): Chart 35. Friendly Islands: 21d16'S 174d44'E Terraserver: 21d17' 174d55' Er:-1', -11' Chart 55. N point Hawaii isl: 20d17'N 156d00'W Terraserver: 20d16' 155d52' Er:+1', +8' Karakakooa bay: 19d28'N 156d00' Terraserver: 19d28'N 155d56' Er:-0', +4' Chart 57. Aivatcvhka bay: 52d54'N 157d33'E Terraserver: 52d56' 158d28' Er:-2', -45' Another point there:52d51' 157d48' Terraserver: 52d53' 158d42' Er:-2', -54' The average absolute error in latitude is 2.3'. The average absolute error in longitude is 33' (36' in the first voyage). This corresponds to a Lunar distance measurement accuracy of about 1', approximately. I may conclude that the measurement accuracy was about 1', and extra 1' in latitudes comes from the horizon (or perhaps they used wood quadrants instead of metal sextants for altitudes, as Norrie advises:-) The log of astronomical observations shows that enormous number of measurements was made for each Lunar, with 3 or 4 sextants and different observers. It seems that to determine longitudes of important points on the shore they made around 100 measurements altogether for each such point. It is interesting to find out how much of these errors is due to the almanac errors. Alex. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---