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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Altitude correction using Artificial Horizon?
From: Dan Allen
Date: 2000 Sep 05, 10:27 PM
From: Dan Allen
Date: 2000 Sep 05, 10:27 PM
There are several corrections for a sextant reading. Dip, refraction, parallax, and semi-diameter are the main correction variables. (Index error, or the innate sextant error, is more of an individual constant that varies sextant to sextant.) Dip and semi-diameter are not needed when measuring an angle with an artifical horizon. Why? Dip is a function of height above the horizon, but since the horizon is not being used (an artificial one is instead), dip does not apply. Semi-diameter is often not used when measuring the sun and moon when using an artificial horizon, as you can center the body and dispense with this correction, but if you measure to the upper or lower limb, then you still need it. Parallax and refraction still need to be applied. Both of these depend upon the angle observed, while refraction is also a function of temperature and barometric pressure. These are combined in most sight reduction schemes are are often referred to together as an "altitute correction". Dan Allen -----Original Message----- >> Is it necessary to apply any correction for altitude when reducing a sun >> sight taken with an artificial horizon? Kirk Benson 34d 10.8' N 84d 12.7' W
