# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Lunar Distances with Alex's SNO-T
From: Bill B
Date: 2006 Nov 02, 03:57 -0500

```Alex wrote

> I wonder where Frank does it in Chicago:-)
> I am thinking more of outdoor places,
> like Celery Bog, etc.
> 500 feet we need because the angles involved are
> very small.
> Indeed, suppose your IC is 0.1' and you want to detect it.
> the distance between the sextant mirrors is
> about 2 inches. The two rays inclined at 0.1'
> issued at a distance 2 inches will be still 2 inches
> apart if you walk moderate distance from the sextant.
> So you see nothing.
> You have to walk far away for the rays to diverge by
> 2.1 inches, so that you can see the difference.
> Simple computation shows that for this you have to
> walk 260 feet away. But the difference between 2 inches
> and 2.1 inches is quite small... So it is better to walk
> twice that much.

Agreed.  If outdoors will work in a November with December temperatures, how
about the old K-Mart parking lot?

A TV table, low wind, and a narrow piece of poster board mounted to a level
(so we don't screw up the dot-to-dot readings with an off-plumb target)
should do it.  A pair of fine-point dividers to establish center-to-center
or edge-to-edge distance and an engineering rule should get us within 0.1"
to 0.25" of dot-to-dot.

I still have reservations about dot size due to focus at 50 ft vs. 500 ft,
and the if we can use the focus setting we use in real life, but I'm game.

Bill

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