Maybe Letronne on the waning moon terminator

This did not work out for me this time, but I will make a point of sketching these areas on the moon anyway and see how it goes.

Deirdre Kelleghan
Irish Astronomical Society
www.irishastrosoc.org

This is Mersenius as sketched by me on November 2nd between 17:35 UT - and 18:15 UT
Bray Co Wicklow Ireland
Humidity 90%Temp 3C
Rite in the Rain paper Staedtler 2B, 6B pencils
Lat: 53:11:44N (53.1955) Lon: 6:06:31W (-6.1086)
Seeing 2
Transparency Average

Sky Watcher 200mm FL 1400mm
Eyepiece 8mm TVP

The hilly region between the western edge of Mare Humorum and the western limb of the Moon. Clefts and furrows run parallel with the edge of Mare Humorum. - Rukl

I will catch this again when it presents a bit better, Letronne was even more bleached out than Mersenius. So another time for both.

Deirdre

Deirdre -

I finally got a chance to make an observation of the early morning crescent Moon with a lighting approximating that of your sketch from last summer. I am not much of a photographer, but I have posted a crude through-the-eyepiece image at:

www.flickr.com/photos/14421319@N00/389372485/

The photo was taken this morning (California time) when the sun angle over Mersenius was almost identical to that at the start of your August 20th sketching session from County Bray (local sun angle = 5.8 degrees). It turns out that Letronne is completely in darkness when the sun is at this angle; so your and Peter's identification of this drawing as one of Mersenius certainly seems correct now.

I was quite surprised to see Mersenius looking, at this hour, like an almost perfect mirror image of Piccolomini with the peaks of the NW wall of Mare Humorum jutting out of it into the darkness very much like Rupes Altai juts out of Piccolomini. I hadn't expected this from the maps and drawings I had seen, but I see now that you described these peaks in your original commentary.

As the photo shows, the east wall of Mersenius is brightly lit even though the drawing shows it as a kind of gray open bay (giving the resemblance to Letronne). As the previously mentioned photo by Jan Simons shows, the east wall remains bright even when the Sun is as low as 2.5 degrees (well after your sketching session had ended); but by then the chain of peaks has completely disappeared.

I hope this helps to solve the mystery.

-- Jim Mosher

WOW !! Jim many thanks for taking the trouble to take a photo of this area in the same lighting conditions. I really appreciate the detail in which you have observed my sketch and the time you have put into this middle of the night mystery.

Looking at your photograph, the very strong black curved shadow plus the line of sunlit peaks of the NW wall of Mare Humorum which you captured in your image. This reminded me how visualy striking that was when I was observing at that time. With everything else taken into consideration yes it looks like Mersenius WINS.

Thanks to eveyone who took an interest in this lunar journey, I am much more careful now to ID my target before I sketch no matter what hour I am standing in the chrysanthemums

Deirdre Kelleghan
Irish Astronomical Society
www.irishastrosoc.org