NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
An interesting question
From: Lu Abel
Date: 2013 Oct 10, 11:19 -0700
From: Lu Abel
Date: 2013 Oct 10, 11:19 -0700
from a student in my celestial navigation class:
If one were on the Great Plains (of the US, for our non-US members)
could one take a sextant shot and get a LOP with reasonable accuracy?
The Great Plains are a vast area of what appears to be totally flat land.
My first instinct was (and still is) to say "no." I don't believe the
human eye could distinguish a one degree slope in the ground, and so the
Great Plains easily could undulate.
But I also wondered if I were lost in my covered wagon with nothing but
a sextant and a Nautical Almanac, could I get a reasonable LOP?
I've driven from St Louis to Denver. You cross vast areas of what
appears to be totally flat ground ("on a clear day you would be able to
see Pike's Peak except for the curvature of the earth" was a saying when
I was a student at the University of Illinois).
Let's assume it's truly flat ground. Back of the envelope, the
distance is 1000 miles and the elevation gain is one mile. That's a
right triangle with a hypotenuse of 1000 and an opposite side of 1.
Sine of a small angle is approximately equal to the angle itself
expressed in radians. So the angle is 1/1000 radians or 3.5 minutes of
arc.
Assuming no undulation in the ground, getting a LOP that's off by 3.5
miles ain't bad.
Thoughts/comments?
