POSITION by MERIDIAN PASSAGE

We spotted Pelican Pete rowing ashore with all his empty water jugs
 in the midst of a water run.  Most cruising sailors rarely tie up to a dock,
 preferring the economy of being at anchor, so they ferry all their water 
and supplies by dinghy.  This can be a rigorous task, where Pete may not be in 
a cheery mood at the end of it, so we decided to ask him a pending question now.

“Pelican Pete, were you going to mention some alternates to the Intercept method?”

“Yes”, Pete replied.

Meridian Passage is the next method that comes to mind.  
This includes the traditional Noon Sight where the daily run for the last
 24 hours is determined.

I call it “calculator-less navigation” because all it requires is simple addition 
and subtraction with a pencil and paper. 
With the simplicity comes limitations:

1. There is only one Meridian Passage per body, per day.
2. You need a continuously clear sky and horizon for 5 or 10
    minutes before and after the passage. 

Using the techniques outlined in any celestial navigation text book, find the
GMT time of the passage and the sextant angle (Hs) of the body at its highest point.
For the sun, this is Local Apparent Noon (LAN).  

The Hs is corrected for Atmospheric refraction and Dip using the tables in the 
Nautical Almanac.  For the Sun and Moon, combine the Semi-Diameter (SD). 
For the Moon, you will also need to combine the Horizontal Parallax(HP). 
The SD and HP are found in the Almanac.
The Hs combined with the corrections equals the Ho (Height observed).

Then go to the Daily Pages and the Increments and Corrections table in the almanac
to get the Greenwich Hour Angle (GHA) and Declination (Dec) of the body at the 
time of the Meridian Passage.  The Ho can be combined directly with the Dec of the 
body to get your latitude, and the GHA of the body can be converted to your longitude, 
all with a little simple math!

To be continued...