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    Re: Sun sights during an eclipse: "bad limb" calculation
    From: Antoine Couëtte
    Date: 2023 Oct 3, 05:51 -0700

    Hello to all,

    Further to my earlier "stand by" reply, and without adequate time yet to work it out entirely; partial reply only hereafter to this initial puzzle in which two questions were asked.

    (1) - Moon UL or Moon LL ? (See top of attachment).

    You cannot escape here using the local horizon and zenith.

    Hence simply consider Sun (height, azimuth) and Moon (height, azimuth) as their (Lat, Long) and draw a GC from Moon Center to Sun center. Moon Departure angle immediately indicates which is the Limb to be used. (See top of attachment).

    (2) - Sun Bad limb or not ? (See bottom of attachment).

    Use a moving local grid centered in S1 onto the Sun bottom Limb (Upper Limb) and from 2 adequately separated times T(1) and T(2), draw the relative Moon center positions.

    Work out everything as linear (i.e. relative Moon altitudes / Azimuths and Moon SD), ignore differential refraction in a first time - and check the times for which S1-Moon Center exactly equals Moon Semi-Diameter. Inside this time-frame, S1 is hidden the Moon, hence Sun LL cannot be used Outside such time frame Sun LL can be used.

    Same approach for Sun UL.

    That's not perfect, but does constitute a good and solid start up point.  (See bottom of attachment)

    Note : If Moon SD greater than Sun SD, there is a possibility that both Sun UL and LL can be "obscured" at one same moment.

    Time permitting, I will work out and publish this detailed example (Oct 14th, 2023 and suppose you're near 28.00° N, 90.00° W at noon time).

    Kermit

    File:
    231003-Sun-sights-during-eclipse-(Bad-limbs-calculation)-.pdf
       
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