NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2012 Jul 19, 09:06 -0700
1. Apply dip and index correction to back sight (hs) Moon lower limb.
115* 11.9' (hs)
-2.7' dip
0 I.C.
115* 9.2' (ha) back sight lower limb
2. 180* - 115* 9.2' = 64* 50.8' Moon upper limb (ha)
3. 64* 50.8'
- 0.5' refraction
-15.0' semi diameter upper limb
+23.0' parallax HP 55
64* 58.3' (Ho)
4. 64* 58.3'
-8* 52.0' N. Declination
+ 27.5' ex-meridian correction
56* 33.8'
5. 90* - 56* 33.8' = 33* 26.2' N. Latitude
For ex-meridian correction
(a)=3.9 (t)=20.6
(a)(t^2)/60
(3.9)(20.6)(20.6)/60 = 27.6' added
The ex-meridian Moon back sight reduction is a convoluted affair which explains why most CN practitioners avoid this observation.
Greg Rudzinski
[NavList] Moon Lower Limb Ex-Meridian Back Sight
From: Greg Rudzinski
Date: 14 Jul 2012 15:16
Here is an ex-meridian back sight taken through a light haze to a sharp horizon while on an island mooring. What cove am I moored at ? This observation was extremely difficult even while on a mooring. Finding the Moon required observing the Moon to a short horizon then setting the sextant to 180 - the sextant reading. Even then getting the Moon into the field of view had me twisting about with my back to the Moon.
7/10/2012
UT 13:40:50
Hs 115* 11.9' Lower Limb (back sight)
Height of Eye 8 ft.
Index Corr. 0.0'
(a) =3.9
(a)(t^2)/60 = added XM correction
Semi Diameter 15.0'
HP 55.0'
Declination 8* 52.0' N
GHA 123* 39.6'
LHA 5* 9.7'
Time After Meridian Passage 20.6 minutes
Greg Rudzinski
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