NavList:

Polaris would be the observation of choice for determine latitude with the artificial horizon provided the canyon walls do not obstruct. At least a 4 power scope is recommended on the sextant due to the low magnitude brightness of Polaris. The Sun on the prime vertical would be the observation of choice for determining longitude by time sight.

Re: Horizontal Sextant Angles and False Horizons etc.
From: Greg Rudzinski
Date: 2013 Jun 7, 07:57 -0700
Sam,

Good luck on documenting and retracing the Powell Expedition of 1869.

http://en.wikipedia.org/wiki/Powell_Geographic_Expedition_of_1869

A worthy project ! Keep us here on NavList informed on your progress.

Greg Rudzinski

Horizontal Sextant Angles and False Horizons etc.
From: Sam Willis
Date: 2013 Jun 6, 08:44 -0700
Hello everyone. HELP!

I am involved in a project that will involve the use of sextants in the Grand Canyon.

1. We will need to use a false horizon because we are in the middle of the desert. Am I right in thinking that a) using a false horizon makes it very difficult to shoot the stars? and that b) because of our lattitude (36) and the declination in August, I will not be able to do a Mer Pass on a 120 degree sextant because the sun will be too high to use a false horizon [and double the angle]?

2. It would be great to do some exercises with horizontal sextant angles. Can someone advise me on this because I am unfamiliar with it. Do I need a special plotting tool?

many thanks
Sam Willis

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