The solar activity is waning, but the sun still manage to produce some nice spots. Like these ones.
Lunar domes Mons Gruithuisen Delta and Gamma can be found in the moon’s northwestern quadrant, between prominent crater Mairan, and not so prominent Gruithuisen (neither of which are captured in this sketch). The two domes are the features in the center of the sketch, with Gruithuisen Delta to the left and Gruithuisen Gamma, which has been said to resemble an upturned bathtub, to the right.
During the observation my eye was drawn to a small feature just north of Gamma. It actually consists of two small adjacent craters, but with the sun angle at the time of the observation, they looked like one crater with a very thin and shiny white ‘bridge’ traversing the darkness of the crater’s interior. The view was truly mesmerizing, especially as the feature after some time seemed to detach itself from the crater wall. There is of course the infamous O’Neill’s bridge on the western shore of Mare Crisium, and it struck me how easy it is to be fooled by the moon’s ever changing lightning conditions.
I haven’t been able to use my telescopes for a couple of months, but the Mercury transit couldn’t be missed. Back home after work I set up and began observations at 15:00 UT. I was treated with a clear blue sky and acceptable seeing. For the observation I used my trusted 10″ SkyWatcher dobsonian, masked down to 4″, and a 17 mm Baader Hyperion eyepiece (for 70x). I followed the transit for about an hour and a half. By that time the sun had dropped towards the horizon and the seeing deteriorated.
Not as impressive as the Venus transit a couple of years ago, I still found the slow progress of Mercury over the face of the sun fascinating to observe. The planet was small, very distinct (of course), and nicely framed by to sunspot groups: AR2542 the larger group at the bottom and AR2543 close to the center of the solar disc. The direction of Mercury’s movement was difficult to pinpoint, and might be a bit off.
I also tried to capture the event with my (handheld) cell phone. Below is the best of several tries.
Rising 1100 meters above the mare in the northwestern part of Oceanus Procellarum are a concentration of lunar domes collectively known as Mons Rümker. The mountain is 70 km in diameter and astronomers have counted 30 domes on it’s slopes.
Observed at low sun, but with mediocre seeing, I was able to readily discern one of the domes — the central peak in the sketch. Comparing my sketch to the image from Lunar Orbiter 4, inserted below, I seem to have caught traces of at least three additional domes.
At first glance nr 36 on the Lunar 100 list — the Grimaldi Basin — seems to be an easy catch. Its quite big and easy to spot in the lunar landscape. It is even just about visible naked eye. But the basin as such is not enough to tick off L 36 — you need to trace both its “outer and inner rings”, and that is a more demanding task.
Preparing for my observation I consulted a number of maps and images to make sure that I had a pretty good idea of where to look for traces of the rings. Still, and at the telescope, the outer ring was far from obvious. Some parts stood out alright, especially on the eastern side, others were more difficult.
Covering such a large area it took me almost an hour to complete the sketch. Even so some parts were sketched rather haphazardly, and especially the southern parts could have used more attention.
One evening last week, while inspecting the terminator, I came across the Encke crater. The illumination was favorable and I decided to give it at go at the sketching pad. Starting out my eyes were soon drawn to a spiky pattern closer to the terminator. I have recently bought a copy of Harold Hill’s wonderful A Portfolio of Lunar Drawings, and I immediately recognized the spikes from one of his drawings (p. 70-71). I decide to extend the range of the sketch and to try to render both Encke and the shadows cast by the remnants of Maestlin R.
Maestlin R draws it’s name from Maestlin, a small and rather unassuming crater just to the north of it (bottom right in sketch). The spikes are created by a series of peaks in the degraded crater wall and cast on the smooth mare. At the time of the sketch the western wall of Maestlin R shone brilliant white, creating a striking contrast.
Encke is a rather large, polygonal and floor-fractured crater. Several ridges were seen on the floor, most notably a ridge traversing the floor from north to south.
Mike Wirth have imaged the area under similar illumination. The image can be found on LPOD.
On 10 February 2014 I made a sketch of lunar crater Gassendi. At the time I was just starting out in lunar observing and this was my first sketch of a major lunar crater. It goes without saying that I found the task quite challenging. Yesterday, and almost two years down the road, I had the opportunity to make a new sketch of Gassendi.
At both occasions Gassendi was sketched under similar (but not identical) lighting conditions and with good seeing (4/5). This means that the differences between the two sketches are due not to atmospheric conditions or the sun angle, but rather to my experience as a lunar observer.
After many years of deep sky observing I know from experience that the hours spent at the telescope slowly increases your ability to see faint details and to observe low contrast object. But when I started out doing lunar observations I would never have guessed, that the hours spent gazing at comparably bright and contrasty lunar features, would have a similar effect. Obviously they did. My sketching techniques has improved somewhat (still a long way to go), the precision in the depiction is better, but most notably I am happy to see that my attention to detail have increased.
I will try to return to Gassendi in the years to come. Hopefully the next sketch will show some further improvements.