NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2019 Dec 5, 08:30 -0800
Frank,
On December 4th you wrote that the phrase 'longitude by chronometer' is "not really" another name for a 'time sight'. However, on September 26th you wrote that "...the expression "longitude by chronometer" was British "slang" for what we call a time sight today. So that's the same thing really." The Wikipedia article I mentioned does indeed describe several different methods for finding longitude. I must admit that I am unfamiliar with the one which "... calculates the 'True Hour Angle' which is compared to the assumed longitude providing a correction to the assumed longitude." But it seems to me to differ only slightly from the method described as a 'time sight' later in the same article. Also, a noon sight for longitude can, of course, be called a kind of longitude by chronometer. But it has been my impression that the former was/is considered an entirely separate sort of method. Am I way off base here?
You also wrote that "The presence of the chronometer is irrelevant ...". Of course I understand what you mean about finding the hour angle and what you wrote later about not needing to bother with the conversion to time. I even mentioned that in my original message. But I'm not sure I understand why a chronometer would be irrelevant - given that one still needs to find the GHA of the Sun at the instant the sight was taken. Unless you only meant to highlight the fact that the process as a whole isn't really about time.
Regards,
Sean C.
