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Bill, you wrote:
"Before I reinvent the wheel  yet a again, does the laser have to be a point
source, or could one that  projects a line segment work?"

A line segment is fine. But shoot it  through a small telescope, sextant or
otherwise, and see if you can make it  narrower at 15 or 20 feet range. Most
lasers diverge considerably in accordance  with the inverse-square law, even at
this range (your line segment will "blur"),  but you can focus them at any
desired distance.

And:
"Do you point the  laser at the front or back of the sextant scope?"

Pointing into the  eyepiece (on the observer end). This whole thing depends
on the reversibility of  optics light paths. So picture your eye as an emitter
instead of a receiver of  light. Put the laser where your eye belongs when
using the sextant, and the rays  that the laser emits correspond *exactly* to the
rays that your eyes would  receive from a distant source --they're just
travelling in the opposite  direction at every optical surface (or a bit more
physics-y, they're all  time-reversed).

-FER
42.0N 87.7W, or 41.4N  72.1W.
www.HistoricalAtlas.com/lunars

   

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