NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2017 Jan 20, 19:11 -0800
I have made a first attempt at reducing Blackburne's sights. The latitude is within 0.4' of the GPS position but the longitude is over 2° in error. I will append details of my working.
- Is my procedure correct?
- Have I made an arithmetical error?
- Have I applied Eot with the correct sign?
Sight 1
Dec 2° 56' 54" N (2° 56.9')
Ho 44° 14' 04" (44° 14')
MTG 13h 17m 31s
EoT 5m 13.3s
It is pre-1925 so Greenwhich time starts at noon. Therefore GHA = GAT. I tried adding and subtracting EoT - adding gave a more sensible answer i.e. GAT = MTG + EoT.
GAT = 13h 22m 44.3s
From Norie's Time to Arc tables I get
GHA = 200° 41'
Sight 2
dec 2° 59' 24" N (2° 59.4')
Ho 25° 45' 30" (25° 45.5')
MTG 15h 51m 18s
EoT 5m 11.3s
From which GAT = 15h 56m 29.3s
From Norie GHA = 239° 7.25'
Solution
When I insert these numbers into the Vector Solutions 2CoP app the position is
41° 17.2' S
172° 11.8' E
The GPS position is
41° 17.57' S
174° 47.36'
