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Bill,

I found that the key for me was to spend time learning the coordinate
systems carefully, early on in my training.  I still keep going back to the
basic definitions and diagrams to remind myself of the terminology and
relationships.  You might find these images and explanations helpful, maybe:

Bowditch's glossary always keeps me on track:
http://www.i-DEADLINK-com/bowditch/
http://pollux.nss.nima.mil/pubs/pubs_j_apn_sections.html?rid=187
www.marineplanner.com/bowditch/bowditch.cfm

Upper branch. That half of a meridian or celestial meridian from pole to
pole which passes through a place or its zenith.
Lower branch. The half of a meridian or celestial meridian from pole to pole
which passes through the antipode or nadir of a place.
See Bowditch Figure 1524a.
You can see a body crossing the lower branch of your meridian from your
position in certain situations.
(I have a hunch that the terms "upper" and "lower" come from class-conscious
European culutures pre-1900, when everybody on the same side of something
was "upper" crust, and all the rest were "lower"?)

Coordinate Systems in CN:
http://jimthompson.net/boating/CelestialNav/CelestNotes/Coordinates.htm
(in particular the section on the Navigational Triangle near the bottom,
where there are a couple of diagrams for meridian crossings of the upper and
lower branches.)

Meridian Transit sight reduction:
http://jimthompson.net/boating/CelestialNav/CelestNotes/SightReduction.htm#M
eridianTransit

Noon Sun:
http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm

Jim Thompson
jim2@jimthompson.net
www.jimthompson.net
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