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Dave,

Attached is a Sumner Line plot for your pseudo example using The Martelli Tables to solve longitude at two different latitudes.

Greg Rudzinski

From: David C
Date: 2016 Jun 27, 20:27 -0700

I am having trouble with  a time sight, which I am using to plot Sumner lines (by his original method). If I use a pseudo PM sight  the Sumner line passes through my location. However if I use a pseudo morning sight the calculated longitudes are completely wrong and the Sumner line  slopes the same way as the PM sight. This suggests that the problem is with W or E meridian angles.

Can someone please check my working which is as follows:

(a) Calculate Hc from pseudo sight.

27/06/2016 0900 NZST (+12)

26/6/2016  2100 GMT

GHA  134° 14.9'

Dec 23° 18.8'

Assumed lat S41°

Assumed long  E174° 44.4'

LHA 309° 19.9'

Hc 11° 1.2'

Zn 46° 12'

(b) Calculate longitude for two latitudes to plot a Sumner line.

27/06/2016 0900 NZST

26/6/2016  2100 GMT

GHA   134° 14.9'    134.25°

Dec 23° 18.8'

Ho  11° 1.3'

Lat 1  S40 t1= 50.66 = 50° 39.6'  long  184° 54.6'

Lat 2 S42  t2 = 48.03 = 48° 1.8'   long 182° 16.8'

The logitudes clearly wrong and the Sumner line (if I plotted it) would slope the same way as the PM sight. Also, shouldn't the long for lat S40 be E174° 44.4'? I have tried just about every combination of t, GHA, 360 and 180.

Any help will be appreciated.

As an aside I am very happy. This morning I visited a local second hand book shop and went to a section that I had picked over recently.  A slim volume attracted my attention. I picked it up and it was a 1938 copy of Ageton in pristine condition. Glancing through the instructions I see that I have some serious study ahead of me. Then when I arrived home there was a note from a courier to say that a parcel could be picked up at his local depot. The relevance? It will be the artificial horizon I ordered from Celestaire last week. Now I need a day when a lack of commitments and a lack of clouds coincide (-;

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