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    Re: Unexpected USNO height correction precepts
    From: Andrés Ruiz
    Date: 2018 Sep 27, 13:23 +0200

    Dear Antoine,

    thanks for your comments. Interesting, as always.


    “Opinions about publishing Planets GCL's instead of Planets GCM's in the Nautical Almanacs ?”

    I prefer GCM è

    For Venus 1977/03/18

    ·         phase angle φ = 139°

    ·         illumination = 12.09 %

    ·         SD = 0.42 moa

    The attached simulation on how Venus appears is taken from Stellarium.

    So I would have been tempted to use the lower limb and correct for SD.

    Easier than a phase correction.


    When the illumination of the Moon is near “Full Moon”, at night the line of the horizon could be false due to the reflections. Great error.

    As this case of Venus, I try to avoid these kind of weird sights.


    If you eye is sharp enough and ones can see the spot of light, or the limb it is not necessary, isn't it?

    I mean:

    If you eye is sharp enough and one can see the spot of light, or the limb; the phase correction is not necessary, isn't it?

    Yesterday I was cheking:

    Date UT1 Body GHA Dec SD HP RA Illumination Zn Hc
    26/09/2018 18:16:17 Venus 64º 46.9' -20º 39.5' 0.36 0.38 14:19:09 21.01 237 03º 58.67'
    26/09/2018 18:16:17 Mars 331º 48.5' -23º 10.6' 0.14 0.26 20:31:03 89.08 151 17º 56.74'
    26/09/2018 18:16:17 Jupiter 50º 29.4' -17º 20.1' 0.27 0.02 15:16:19 99.52 228 14º 49.57'
    26/09/2018 18:16:17 Saturn  6º 27.0' -22º 45.0' 0.14 0.01 18:12:29 99.75 184 23º 48.41'



    My applications calculate the SD for planets and the user could choose limb = UL/C/LL. User decision…

    But to be honest, when I shoot planets, I always treat them as a spot, as my eye, till now, is able to discern and interpolate the center, and no correction for SD is taken into account.

    Fair winds!
    Andrés Ruiz
    Navigational Algorithms


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