Lunar Limb Profile & Partial Solar Eclipse

[Peter Meadows]

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.

[Alex Pratt]

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.

Attachments:

1. 

   Occult-Bailys-Beads.png
   

[Alex Pratt]

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.

Attachments:

1. 

   Cirencester-Occult-lunar-limb-plot-inverted.png
   

[Peter Meadows]

Hi Alex,

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

Best wishes,

Peter

[Alex Pratt]

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.

[Alex Pratt]

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.

Attachments:

1. 

   Cirencester-Occult-lunar-limb-plot-inverted-transposed.png
   

[Peter Meadows]

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.

Attachments:

1. 

   NS_20221025_0953UT_limb_profile.jpg
   

[Alex Pratt]

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.

Attachments:

1. 

   York-20221025_0953-Occult-Lunar-limb-plot-inverted.png
   

[Alex Pratt]

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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