NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ed Popko
Date: 2016 Aug 30, 15:05 -0700
Tony,
I'm unskilled at explaining math sequences but I'll give it a try. If you search the NavList archives you will find some very good discussions about why prop logs came to be and how tables were created. Jeff Gottfred's "Lunar tables - use of prop logs" is a very good post. See: http://fer3.com/arc/m2.aspx/Lunar-tables-use-prop-logs-Gottfred-jan-1995-w804 for a complete explanation.
So it boils down to this ..
pLogt = pLogd - pLogD
Where ...
D is total change in LD distance from first time (12:00) to last time (15:00) in bracket. Three hours or 60x60x3=10800 seconds.
Using your post data ...
D = 84° 35.2' - 82° 56.8'
= 1° 38.4'
Looking 1° 38.4' up in table ...
pLogD = 2766
and ...
d is total change in LD distance from First time (12:00) to your unknown time of lunar sight
d = 84° 35.2' - 83° 00.0'
= 1 35.2'
Looking 1 35.2' up in table ...
pLogd = 2623
Thus ...
The pLogt is their difference
pLogt = 2766 - 2623
= 143
Looking up 143 in table falls between tabulated 142 and 145, so I guess it is about 02:54:09
Add this offset (time of your lunar from first time bracket)
12:00:00
+ 02:54:09
-----------
Time of lunar 12:54:09
Ed Popko
