NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bligh's noon by chronometer
From: Jeremy C
Date: 2010 Jun 3, 07:46 EDT
From: Jeremy C
Date: 2010 Jun 3, 07:46 EDT
George wrote:
It could be taken up to an hour or more either side of noon,
whenever a glimpse of the Sun appeared
through the clouds. And then, the latitude could be readily calculated
from the altitude at that moment, knowing the time difference from noon,
using the Ex-meridian Tables. That was primarily what those tables were
for.
======================
through the clouds. And then, the latitude could be readily calculated
from the altitude at that moment, knowing the time difference from noon,
using the Ex-meridian Tables. That was primarily what those tables were
for.
======================
Were the tables altogether different than modern tables? The
current Bowditch tables don't calculate beyond a meridian angle of 7
degrees, or around 29 minutes of time.
The formula also falls apart close to noon near the equator
so much so that they are not even presented. I have run into that problem
several times when trying to shoot ex-meridians when Hs is above 80
degrees.
More to the point, I am starting to shoot sun at meridian transit not
based on highest altitude but rather by calculated time to avoid the errors due
to ship's motion. I am getting much more accurate results in Latitude with
this method. I have always used this method when shooting the moon,
planets or stars at transit.
Jeremy