NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars: Jupiter's BIG.
From: Frank Reed CT
Date: 2003 Dec 23, 17:40 EST
From: Frank Reed CT
Date: 2003 Dec 23, 17:40 EST
Fred you wrote:
"I believe that to _rate_ a chronometer one needs at least three lunars spread over at least three days. "
Just one lunar will do. When you leave port, you know your chronometer's error (assuming it's a port with a well-established longitude). Let's suppose it's sixty seconds slow as you depart. After five months at sea, you get some measure of your longitude. This could be from speaking another ship, from visiting a port, OR from shooting a lunar. Suppose your chronometer now appears to be 4 minutes fast. That means it's gaining 1 minute per month. That's the rate.
On the other hand, there is some benefit in doing lunars for a few days in a row. Primarily, this would assure you that you didn't get an accidental close match from your first trial. You could also get the same result by having several navigators shoot lunars each working up an independent longitude. This was certainly the case on at least some American ships at mid-century.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"I believe that to _rate_ a chronometer one needs at least three lunars spread over at least three days. "
Just one lunar will do. When you leave port, you know your chronometer's error (assuming it's a port with a well-established longitude). Let's suppose it's sixty seconds slow as you depart. After five months at sea, you get some measure of your longitude. This could be from speaking another ship, from visiting a port, OR from shooting a lunar. Suppose your chronometer now appears to be 4 minutes fast. That means it's gaining 1 minute per month. That's the rate.
On the other hand, there is some benefit in doing lunars for a few days in a row. Primarily, this would assure you that you didn't get an accidental close match from your first trial. You could also get the same result by having several navigators shoot lunars each working up an independent longitude. This was certainly the case on at least some American ships at mid-century.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
