# NavList:

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

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Re: Corrections for use of artificial horizon at 1,000' MSL?
From: Gary LaPook
Date: 2012 Mar 13, 17:57 -0700
Here is another refraction table for use in flight which, obviously, is above sea level. Both of these tables are for use in flight navigation so are only tabulated to the whole minute so you would be better off just using the Nautical Almanac sea level tables for your altitude of 1,000 feet.

gl

--- On Tue, 3/13/12, Gary LaPook <garylapook---.net> wrote:

From: Gary LaPook <garylapook---.net>
Subject: [NavList] Re: Corrections for use of artificial horizon at 1,000' MSL?
To: NavList@fer3.com
Date: Tuesday, March 13, 2012, 2:44 AM

 I have attached a table showing corrections for altitudes above sea level. Comparing the temperature corrections for sea level and for 1,000 feet you can see the 1,000 foot values are 96% of the sea level values, only a 4% difference which can be safely ignored, so just use the standard table in the Nautical Almanac.Remember to touch the bottom of the image of the sun in the sextant index mirror to the top of the sun reflected from the artificial horizon which produces a lower limb observation. Apply the index correction then divide by two. Then apply refraction and semi-diameter (or the combined correction found in the Nautical Almanac) but DO NOT apply dip.glgl--- On Mon, 3/12/12, Scott Statz wrote:From: Scott Statz Subject: [NavList] Corrections for use of artificial horizon at 1,000' MSL?To: NavList@fer3.comDate: Monday, March 12, 2012, 11:33 PMI live in Madison, WI, at about 960' mean sea level. I am teaching myself with the help of CELESTIAL NAVIGATION BY H.O.249 by John E. Milligan and am still working my way through the book. When using an artificial horizon, do I need to be concerned with a special correction for refraction (anything else at this altitude or in my circumstance)? I understand its not necessary at sea level and there are concerns when taking a sight at low angles.ThanksScott----------------------------------------------------------------NavList message boards and member settings: www.fer3.com/NavListMembers may optionally receive posts by email.To cancel email delivery, send a message to NoMail[at]fer3.com----------------------------------------------------------------

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