Lunar Limb Profile & Partial Solar Eclipse

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  • #613275
    Peter Meadows
    Participant

    During today’s partial lunar eclipse, one of the most noticeable features was the unevenness of the lunar limb. Does anyone know how to generate a limb profile for around mid-eclipse at say 10hrs UT on 2022 October 25? It doesn’t need to be at a very high resolution to enable a comparison with images taken by many BAA members.

    #613276
    Alex Pratt
    Participant

    Hi Peter,

    The comprehensive occultations software suite Occult

    https://occultations.org/observing/software/occult/

    can generate a lunar limb profile for Baily’s Beads analysis (see attached)

    I’ll have a look tomorrow to see if I can extract a limb profile matching our observers’ images.

    Alex.

    #613281
    Alex Pratt
    Participant

    Hi Peter,

    Here’s an inverted plot of the lunar limb generated by Occult from LRO/LOLA data. It’s for the location of Cirencester at 09:50 UT on 2022 October 25 to compare with James Weightman’s ‘Lunar Mountains Silhouette’ image.

    https://britastro.org/observations/observation.php?id=20221025_124443_d85bceb02058323a

    Note that the Occult plot has a linear baseline, whereas the lunar limb is curved.

    I might not have used the correct limb angle in Occult, and as you view the limb in fine detail any discrepancy in the site location and altitude, or error in selecting the cusp angle, can cause a significant difference in the resulting limb profile.

    Alex.

    #613283
    Peter Meadows
    Participant

    Hi Alex,

    Many thanks for generating the limb profile. I’ll see if I can match this to the eclipse images.

    Best wishes,

    Peter

    #613285
    Alex Pratt
    Participant

    Hi Peter,

    If this is unsuccessful, please let me know a site location and time, and PA of the Moon’s limb and we can try that.

    Alex.

    #613320
    Alex Pratt
    Participant

    Limb profiles often require some mental gymnastics. Transposing the plot L-R, so that the PA (Watts Angle) increases from L-R, gives the attached image. Does it match James’ Silhouette?

    It’s tricky to identify the required PA when we need to work from the N point of lunar images presented at various orientations, such as from my alt-az mounted Mak.

    Alex.

    #613384
    Peter Meadows
    Participant

    Hi Alex, I think I have been able to fit your limb profile to one of the eclipse images sent to the Solar Section. The attached image by Nic Spencer is taken in CaK light and nicely show detail on the limb – I’ve match feature in the profile and the limb image as indicated. Is it possible to extend your profile plot to include more of the limb shown in Nic’s image (also Nic lives in York)? If so I think it will confirm the features in the profile and image.

    #613398
    Alex Pratt
    Participant

    Hi Peter,

    Here’s an extended profile for York at 09:53 UT. If we look at too wide a limb segment, we’ll get bamboozled with all the peaks and troughs.

    Cheers,

    Alex.

    #613418
    Alex Pratt
    Participant

    Hi Peter,

    If you look at the region (from about 155 deg. to 170 deg.) in my earlier limb profile, I think it also matches the images from other observers’ high-resolution stills and GIFs.

    Alex.

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