NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2026 May 1, 10:37 -0700
Lars, you wrote:
"passing 3 miles west of the southern point of Brava Island in the Cape Verdes"
Yes, that's the "Brava" mentioned in the upper right corner of this page!
You wrote:
"The altitude is corrected by 10', indicating a fairly large height of eye or possibly some index error is included."
The "normal" quick correction rule was +12 for a Lower Limb sight (Sun or Moon) and -20 for Upper Limb (Moon, with rare exceptions), regardless of actual height of eye or actual refraction. Given that all ocean-going vessels were about the same size (!), -3' or -4' minutes for height of eye was a fair standard. And for refraction 0-1' was acceptable or better yet -2' at this altitude. Then +16' for Sun LL yields something in the range of 10'-13'. This one may be an attempt to be more careful about height of eye or specific refraction values, but my sense is that navigators had personal preferences, and this was not carefully calculated: 10' or 12' seemed to be common. So I drop it in the "navigation culture" file. :)
Frank Reed
