NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Understanding a 1902 Sumner
From: John D. Howard
Date: 2017 Jan 20, 10:26 -0800
From: John D. Howard
Date: 2017 Jan 20, 10:26 -0800
David,
To extract GHA from old data simply apply the EOT to the Greenwitch time and multiply by 15. Up untill 1922 the mean time for use in the almanacs started at noon, so 0100 would be GHA 15 degrees. Now days you need to subtract 12 hours from Zulu then apply EOT and multiply by 15. Remember that apparent time is GHA sun.
The Dec is the same as nowdays, ie the number from the almanac corrected for the time of the sight. On the data sheet it is listed as Cor. Dl ( corrected declination )
Navigators of old only needed a list of daily EOT and declination to do cel-nav using the sun. Star sights were rare. The full Nautical Almanac was needed for lunars and star sights but they were not done much after cronometers became common.
John H.
