Hi everyone,
It’s been four weeks since my last lunar sketch. Not from lack of trying. On those occasions when I was able to pull a
scope out, seeing conditions were dreadful.
The image through the eyepiece was shimmering and boiling so much it was
visible even at 50X magnification.
It was an unexpected long spell of poor seeing, but there
was a silver lining to it!
Last Saturday night I set up my telescope in order to fine
tune its vibration suppression properties.
It was full Moon, and high cloud meant I wasn’t considering doing a
sketch. The testing of the new vibration
suppression tweak worked, which I’m most pleased about. What I did not expect though was the image I
got from the Moon – yet another lesson that needed learning…
Full Moon I had thought of as a shadowless phase of the
Moon. But things are not always what we
think of at first. The Moon’s orbit
around the sun is not in the one flat plane.
The Moon orbital plane is a broad one.
We can see this over a few nights when we compare its position in the
sky when it is at the same point over some landmark. It will be either closer to or further away
from that landmark.
The consequence of this, when the Moon is at its highest
point in its orbital plane, and it coincides with its full phase, we get a view
of the Moon where we can see a thin strip of a terminator. Somewhat like looking under its skirt!
So this Full Moon phase I caught the Moon at, the thinnest strip
of the terminator was visible. And what
was on view was absolutely staggering!
Mountains! Lots and lots of
mountains seen not from above, but side on, and with shadows: dark ridges from crater rims, shadows cast
back from foreground mountains, & valleys between mountain ranges left in
shadow. And beads of light from crater
rims just reaching up from the shadows along the terminator. So much going on all along the limb! And the foreshortening, WOW!
The Saturday was not a sketch night, but the following
Sunday was crystal clear, and the phase was equivalent from Saturday. And with the thrill of the previous night
still fresh in my mind, I knew exactly what I was to chase down – mountains
along the limb!
I settled on a spot with a few dramatic mountains were
clustered, and a large and highly foreshortened crater lay nearby. The clarity of the night was amazing, and the
detail visible on the mountain sides was spectacular. The mountains were not plane white blocks,
but textures and variations in illumination were visible. Like looking at snow-capped mountains in the
distance. And the foreshortened crater
was visible almost like a cross section, where the rise and fall of the ancient
rim was appreciable over both the internal and external walls. And as the sketch progressed, those finer details
of foreground ridges, mountains and craters emerged, casting their thin shadows
backwards.
I felt very privileged to be able to make this piece.
The surprises didn’t stop here for me. Researching the area I sketched, I came to
find it was the area around the Moon’s South Pole. The large crater turns out to be
Drygalski. Never heard of it? Not surprising really. Most maps won’t show this 150km hole in the
Moon. It is visible only for a few days,
and only when the Moon’s libration is favourable and positions Drygalski into
view.
Libration
The Moon’s orbit around the Earth is not a static tidally
locked one. The Moon has a wobble. And it is this wobble that actually allows us
to see not just 50% of its surface, but 60% of it! Yes, we do get a fleeting glimpse of some of
the far side of the Moon.
This Wiki video of one lunar phase, shows the Moon’s
libration over the period.
Drygalski is a rare fish, as it is not seen very often, and
seeing so much of its floor even more so.
Its floor may be visible only two or three times a year for a few nights
at a time. I have been able to find very
few Earth based photos of Drygalski. A
very rare fish.
I hope you enjoy this piece.
Alex.
Object: Crater
Drygalski and Mountains around South Lunar pole.
Scope: C8, 8” SCT
Gear: 8mm LVW, 250X
Date: 22nd
May, 2016
Location: Sydney,
Australia
Media: Soft pastels
& charcoal on A4 size black paper.
Beautiful sketch, as always, of a rare subject. A few months back I went looking for Peary, Byrd, and a few others at the North Pole during full moon. I was prompted by an article in Sky & Telescope. Unfortunately, my knowledge of Lunar geography is still in its infancy, and I couldn't tell one crater from another!
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