NavList:

Everyone,

I have followed the recent posting regarding the subject of determining position from two intersecting circles.  As strange as it may seem this is what I always thought celestial navigators did.  Shoot three objects and get a position on the map and know where they were and then figure out where to go from there.  Little did I know what I was getting myself into.

But I digress.

I live in western Maryland and have absolutely no bodies of water around me that are of any size to use as an artificial horizon.  The nearest lake is about 45 minutes away in a park and they close at sunset no exceptions (I know I used to work there).

I have started to take sights using the sidewalk in my apartment complex parking lot as the horizon line.  It is about 4 inches high and I stand about 20 feet back.  I have been practicing taking sights with a Davis Mark 3 sextant and am starting to attempt to plot the position of the object and determine intersecting circles.  I have also practiced a noon sight to determine my latitude.  I was quite a ways off, so I need more practice.

My question is this, using the sidewalk for a horizon line (and yes it is pretty level), do I need any other special corrections to my sight besides dip, index error, refraction, semi-diameter (in other words the usual things we correct for)? 

Your help is appreciated.

Andrew