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    Re: Noonsite using artificial horizon? Did I do it correctly?
    From: Gary LaPook
    Date: 2014 Aug 26, 10:41 -0700
    The altitude correction tables for the sun found in the Nautical Almanac combine refraction, semi-diameter and parallax. The parallax of the sun is, at most, 8.8", (0.15') and that is only for an observation at a zero altitude. To find the parallax at higher altitudes you multiply this "horizontal parallax" by the cosine of the altitude. For the observation that started this thread, about 60 degrees, the parallax included in the sun correction table is only 0.08' and can be ignored in practical navigation as it is lost in the noise of the actual observation.

    The semi-diameter correction is only applicable to observations of the sun's limbs  to allow the calculation of the center of the sun above the horizon. When using a bubble sextant you measure the center of the sun so you do not apply a semi-diameter correction. Nor do you apply this correction when you superimpose the images of the sun in an liquid artificial horizon since you are also measuring the altitude of the sun's center. You do apply it if you touch the limbs of the sun as seen through the index mirror and the reflected image in the liquid surface. So, when measuring the center of the sun, either with a bubble sextant or when superimposing the sun's images in the liquid AH, you just apply the refraction correction which is listed for the correction for stars in the Nautical Almanac.

    Gary


    From: Dale Lichtblau <NoReply_Lichtblau@fer3.com>
    To: garylapook---.net
    Sent: Tuesday, August 26, 2014 5:36 PM
    Subject: [NavList] Re: Noonsite using artificial horizon? Did I do it correctly?

    Forgive the stupid question, but where does the 1' refraction figure come from..the Altitude Correction Tables 10 - 90?




       
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