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    Publishing Heights values
    From: Antoine Couëtte
    Date: 2017 Dec 26, 04:36 -0800

    RE: EdPopko-dec-2017-g41011

    Dear Ed, or Dear Anybody who can reply to this very simple question ...

    To you all, this post is simply to show to our NavList Community how difficult it can be at times when dealing with published heights, especially when one is not - or no longer - familiar with the US/UK subscripts. I have encountered this obstacle quite often in the past years.

    *******

    As an example among very many RE: EdPopko-dec-2017-g41011 : what does "Ho"  exactly cover for the Moon (Re: Ho 37deg 50.1') ?

    Is it corrected or not for :

    - Sextant error ? I would say that Sextant error is zero here since no indication of Sextant Error. Correct ?

    - Horizon depression ? I would say that from Central Florida the Sextant probably refers to some kind of an artificial horizon (bubble or other), hence depression correction should be taken equal to zero. Correct ?

    - So far, so good, but ...

    - Refraction ? Regarding only the Moon published Ho value, and thinking over it, I really cannot specify whether Refraction correction has been performed or not.

    So I am starting to feel that I might be onto a wrong guessing track here.

    Moreover, if I look at Aldebaran with " Aldebaran Ho 36deg 10.7'  Corr  +01.3' " I am becoming quite puzzled. Assuming that Horizon depression is equal to Zero, the only applicable correction in the case of Aldebaran would remain Refraction. Refraction correction is probably very close to 1.3' (numerically very close from cotangent 36°10'7 as a quick and simple check). So 1.3' definitely has to refer to Refraction, but ... refraction it is a negative correction... so at a first glance I cannot guess what " Aldebaran Ho " exactly refers to. More on this a few lines under.

    - Augmented Semi-Diameter Correction ? Here once again I am am totally puzzled for Lady Moon, since no indication whatsoever is given about any upper or lower limb.

    So I am really lost now. Unless ...

    After some further thoughts, and given that Aldebaran Correction has a sign opposite to the initially expected one, I would think that Aldebaran's "Ho" height is its Geocentric one. And by the same token I would be assuming that the quoted Moon "Ho" Value also refers to its center geocentric height, especially since its quoted correction is also negative, i.e. also opposite to its expected sign.

    Hence, after a few minutes of thinking, I am coming to the conclusion that both published "Ho's" should refer to their geocentric values. Am I right ?

    If this were actually the case, why not clearly mentioning that  "Ho " refers to a geocentric height ?

    When reading that a given published height is "Geocentric", any Reader familiar with CelNav sould then immediately understand that all applicable corrections from Sextant value have been performed and that the quoted " Ho" value refers to the Geocentric Body Center (or if specified, to the "center of light" in the case of Planets Phase Correction altogether with the applicable/relevant Ephemeris available).

    *******

    So, why not indicate more clearly in every case : " Sextant value corrected for horizon depression, refraction, and/or other correction whenever applicable ", e.g. in the case of Ho, simply remind the reader that " Ho" refers to a Geocentric height ? This is not a lenghty task, as I have also seen a good number of our Contributors following this easy and very efficient rule.

    In all cases I would generally favor always publishing "Raw data" - or better "Raw data corrected for [only] Instrument error" altogether with the Observer's environment (height of eye, temperature, pressure). From such data the Reader can "reconstruct" everything (e.g. process published instrument heights into Geocentric heights), and also compare his own results with the Author's "processed heights" whenever these are published, as is the case in Ed Popko's EdPopko-dec-2017-g41011 "First Moon-Star Lunar" post.

    By the way, it is worth remembering that keeping records of ancient "Obervations Raw data" and subsequently processing them again through much more accurate contemporary Precession, Nutation, Aberration and so on ... values has been one of the keys for the superior quality of some of the Planetary Numerical Integrations performed at JPL.

    And by the way also, Dear Ed, thank you very much for publishing your own Lunar. You are hereby joining up a list of Contributors very special to me, such as Greg and our regretted Jeremy among others ... :-) . And you also gave me the opportunity to trigger this topic.

    *******

    Back to basics, I am sure that being more specific when publishing heights would also be beneficial to our entire community since a significant number among us is not of English Culture. Such systematic practice would also reinforce everybody's culture since properly mastering the saga of the height corrections - with such regular informal refreshers - is one of the essential parts of our beloved Auld Allyance between Science and Art in Celestial Navigation.

    As usual, feedback from many of you quite expected and welcome here.

    Thanks you to all for your Kind Attention and Understanding,

    Antoine Couëtte

       
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