L37: Bailly

Bailly is a libration object located close to the southwestern limb of the moon. Traditionally it has been recognized as the largest crater on the nearside of the moon, but today it seems to have been upgraded to a lunar basin (without the defining maria).

The short description in Charles Wood’s Lunar 100 list states that it is a “barely discernible basin”, and that might be so, but as a crater I found it both rewarding and quite straightforward. My observations was done under a 13.7 days old moon, which, in combination with the libration at the time, positioned the terminator on top of Bailly’s far wall, thus creating a nice framing of the view.

At first I was a bit confused by the shadow on the crater floor in front of the far wall — it seemed to be on the wrong side of the wall. My best guess is that this is an effect either of the moon’s curvature and the closeness to the limb, or of a convex shape of the floor as such. The effect is beautifully illustrated in an image captured under similar lighting conditions by Damian Perch (scroll down to B).

Sketch made on 26 September 2015, UT 20:30, using a SkyWatcher 10″ and a TeleVue Nagler 3-6 mm zoom. Seeing 4/5. South is up.

The three parallel strokes above Bailly B (the large floor crater to the left in the sketch) also got me wondering. I have a wage memory of putting them there intentionally, but now a week later they seem odd, to say the least. Again comparing with Peach’s image, I can’t see any structures that might correspond to my strokes. Better just forget about them.

Anyway, I found Bailly a very rewarding object, and I definitely need to return one day.

L44: Mersenius

Mersenius is located west of Mare Humorum not far from the moon’s western limb. It is of average size but still rich in detail. The crater walls are broad and terraced; the floor has been flooded with lava and bulges markedly upwards in the middle.

My observation was done under excellent conditions with steady, transparent skies and favorable illumination. The terraces were prominent, especially on the western side (right i sketch). The convex shape of the floor was indicated by a soft shadow tracing the walls in the northern half of the crater. Two lighter rays were also clearly visible on the floor. (After checking up on the observation it seems that the northern and thinner ray, is a rille rather than a ray.) Several secondary craters were also seen, most notably Mersenius H on the southern part of the rim, and Mersenius L adjacent to the crater on the northern side.

Sketch made on 25 September 2015, UT 21:00, using a SkyWatcher 10″ and a TeleVue Nagler zoom 3-6 mm. Seeing 4-5/5. South is up.

L9: Clavius

Clavius is the third largest crater on the moon’s near side, and it can be found close to the southern limb. The crater is also one of the oldest, which is evident from the many smaller craters that mark the Clavius plain. At local sunrise the two larger of these — Clavius C and D — gives rise to a clair-obscur phenomena, giving the impression of two eyes staring back at you.

My observation of Clavius was done under a 10 days old moon, so I didn’t get to see the Eyes of Clavius (which only shows at 9 days). But the illumination nicely captured the dramatic landscape of the crater. When I started out the seeing was terrible, and I hesitated whether to continue or to call it a night. Eventually I decided to give it a shot, hoping that it might improve after a while. The turbulence settled somewhat as the moon rose, but it wasn’t enough to capture any finer detail.

Clavius C and D are the two largest craters just right of the center. The rim is marked by Porter (top right) and Rutherford (bottom right). The large adjacent crater towards the bottom left is Blacanus.

Sketch made 23 September 2015, UT 17:30, using a Celestron XLT 120 and a TeleVue Nagler zoom 3-6 mm. Seeing 1/5, gradually improving to 3/5. South is up.

Clavius have also made an imprint on popular culture: In Arthur C. Clarke’s 2001: Space Odyssey American activities on the moon are centered around a base build underneath the surface of the crater plain. When Dr Floyd sets out to investigate the monolith excavated in Tycho, he takes the moon shuttle from the Clavius Base.

Clavius Base. Screen capture from 2001: Space Odyssey.

Below is a clip from 2001: A Space Odyssey showing the encounter with the monolith found in Tycho crater. The soundtrack still gives me creeps.

L42: Marius Hills

The largest gathering of volcanic domes on the moon can be found in the middle of Oceanus Procellarum and close to the ring-plain Marius. Squeezed into an area of approximately 200 km in diameter the Marius Hills contains about 300 domes, half of the moon’s known population. The domes are just a few hundred meters high and thus best observed under low sun.

The sketch was made under a waxing gibbous moon, just a few days from full, and the sun angle was perfect for highlighting the many domes. Sketching them was another matter, quite cumbersome at that. Marius is the crater to the middle left in the sketch. Top right is the end of the Reiner Gamma swirl.

Sketch made on 25 September 2015, UT 20:30, using a SkyWatcher 10″ and a TeleVue Nagler 3-6 mm zoom. Seeing 4/5. South is up.

370In 2009 the Japanese Selene mission found what might be a sky light to an underground lava tunnel in the Hills. The Marius Pit is located close to the rightmost dome in the sketch, but since it is just 65 meters in diameter it is well beyond the resolution of my scope. A fly-over movie from JAXA can be found here. Lava tunnels might be an option for a future lunar base, and apparently there is advanced plans for a private moon mission to target the Marius Pit.

L95: Procellarum Basin

The Procellarum Basin draws it’s name from Oceanus Procellarum (Ocean of Storms) and is the unofficial name for a hypothetical impact crater covering a large part of the moon’s nearside. There seems to be at least two alternative explanations to the features associated with the basin, and I will get back to them below.

Working through the Lunar 100 the Procellarum Basin is something of an enigma. What exactly are we supposed to observe? If it is the circular shape that can be traced in the nearside maria, why is it inserted at the difficult end of the Lunar 100 list, and not right after L3: the Mare/Highland dichotomy? So far I haven’t managed to find any information on the web that might shed light on these questions.

Some days ago I had my rarely used 120 mm refractor set up at the kitchen table, doing some maintenance. When done I looked out through an open window and noticed the moon rising over a nearby cliff. Still seated I swung the telescope over and was treated with a really nice view. The indoor/outdoor temperature difference didn’t seem to affect the image, at least not at low power. Comfortable seated I decided to sketch the (almost) full moon, and to try to outline the Procellarum Basin as well as some of the more prominent ejecta ray systems. As the moon would eventually wander out of sight, I had to work quite swiftly, and the sketch was done in about 45 minutes.

Moon observed 28 August 2015, UT 20:30, using a Celestron Omni XLT 120 mm, and a noname Plössl 24 mm (42x). Illumination 98,6 %.

Anyone who have tried to sketch the full face of the moon, know that it is quite challenging. The amount of detail is overwhelming, and it is easy getting stuck somewhere in the highlands, sketching away at the many craters. I decided to go for a rather crude sketch, just outlining the maria and sketching only a few of the craters. I didn’t even bother to trace the terminator — the moon was about a day from full — I just pretended that the moon was a perfect circle.


In the image to the right I have tried to mark what I believe is recognized as the outline of the Procellarum Basin [Edit: see new image at the end]. The maria seems organised in a circular pattern, most notably to the north and southwest, and in accordance with one interpretation it might be traces of an ancient and enormous impact crater. If this is correct the energy of the impact might also have been enough to create the highlands on the far-side of the moon.

IMG_heatingA later and opposing view do away with the impactor, instead claiming that the Procellarum region is the result of internal processes active 3 to 4 billion years ago. Data from the Gravity Recovery and Interior Laboratory (GRAIL) mission show evidence of remnants of lava-filled rifts forming a squarish pattern (red in the image to the right, original image here). It is suggested that as the original lava oceans that covered the young moon solidified, they also contracted. Molten lava then rose at the edges creating the rifts.

If the latter interpretation is true there is no Procellarum basin, which of course again raises the question of what we are suppose to observe. Hopefully I have done enough to tick off L 95 from my list. Come to think of it, and since the sketch also depicts the mare/highland dichotomy, I will tick off L 3 as well.

Edit: After a short exchange with Jef De Wit at Cloudy Nights’ sketching forum, I realized that my depiction of the basin needed to be adjusted. In the paper that suggested the Procellarum Basin (linked in text above), E. A, Whitaker found evidence of three concentric rings associated with the hypothetical impact. “The rings have surface diameters of 1700, 2400 and 3200 km, and are centered at about 23º N, 15º W, near the crater Timocharis.” In the image inserted below I have drawn these circles onto my sketch.

Basin rings

The original Lunar 100 list only mentions the 3200 km ring. And since only a small part of that ring can be clearly seen, and since the impact as such is contested, it might explain why the Procellarum basin ended up on the difficult end of the list.

AR 2403

During the last couple of days a new giant sunspot group has slowly marched across the sun. So far I have managed to make two sketches. The group has increased both in size and complexity over the days, and I have found it quite challenging to sketch.

The sketches below has been rotated to match the images from the Solar and Heliospheric Observatory.

Sketched 22 August 2015, UT 08:00, using a SkyWatcher 10", masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 4/5. (The circle to the right represents the size of the earth.)
Sketched 22 August 2015, UT 08:00, using a SkyWatcher 10″, masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 4/5. (The circle on top approximately represents the size of the earth.)
Sketched 23 August 2015, UT 13:30, using a SkyWatcher 10″, masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 3-4/5.
Image: SOHO/HMI.

AR 2396

The behemoth sunspot AR 2396 is slowly moving across the solar disc, arousing both sketchers and astro-photographers. So far I have managed to sketch it twice, and even if I find it difficult to estimate the size of sunspots, it seems to have grown from one day to the next. Do note that the difference in size between the sketches below does not primarily correspond to any physical developments, but rather to the scale used while sketching.

Edit: I managed to make a third sketch just as AR 2396 approached the limb. Inserted below.

Sketched 8 August 2015, UT 12:00, using a SkyWatcher 10", masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 3/5.
Sketched 8 August 2015, UT 12:00, using a SkyWatcher 10″, masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 3/5.
Image: SDO/HMI.
Image: SDO/HMI.
Sketched 9 August 2015, UT 08:30, using a SkyWatcher 10″, masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 4-5/5.
Image: SDO/HMI.
Sketched 12 August 2015, UT 14:00, using a SkyWatcher 10″, masked down to 100 mm, and a Baader Hyperion 17 mm eyepiece (70x). Seeing 2-3/5.

C/2011 L4 (Pan-STARRS)

Since I started out i amateur astronomy 2008 I have observed 15 comets. Without doubt the most memorable of these was comet C/2011 L4 (Pan-STARRS). It was discovered by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) on Hawaii in June 2011 and reached perihelion i March 2013.

After the passage, as the comet rose from below the western horizon, I made numerous sketches. The comet peaked at magnitude +1, making it an easy catch. It also spawned a beautiful tail.

Beneath are some of my sketches. I used both my dobsonians and a number of different eyepieces for the observations, so please note that the field of view (FOV) varies substantially between the sketches. Also note that during the first and the last observations, the comet hoovered just a few degrees above the horizon making the observations difficult and reducing the comets appearance.

14 mars
Sketched on 14 March, UT 18:30, using a Sky-Watcher 10″ and a Baader Asperic 31 mm (40x, FOV ca 100′).
17 mars
Sketched on 17 March, UT 19:00, using a Sky-Watcher 10″ and a Baader Hyperion 13 mm (92x, FOV ca 40′).


24 mars
Sketched on 24 March, UT 19:15, using a SkyWatcher 10″ and a Baader Hyperion 24 mm (50x, FOV ca 80′).
31 mars
Sketched on 31 March, UT 21:00 using a GSO 16″ and a Baader Aspheric 31 mm (58x, FOV ca 70′).


3 april
Sketched on 3 April, UT 19:50, using GSO 16″ and Baader Apheric 31 mm (58x, FOV a 70′).
5 april
Sketched on 5 April, UT 21:30, using a GSO 16″ and a Baader Hyperion 17 mm (106x, FOV ca 40′).


L41: Bessel Ray

When a lunar crater is formed by an impact, material from the depth of the crust is forced up and catapulted into the surrounding landscape, forming radial ejecta rays. The ejecta material has a higher albedo than the dark maria, making the rays plainly visible. Many lunar craters are associated with ray systems, most notably Copernicus, Kepler, Proclus and Tycho.

The Bessel Ray is a single ejecta ray running almost north-south through the middle of Mare Serenitatis. On it’s way it touches upon the Bessel crater (in the middle of the sketch), giving it it’s name.

Sketched 26 April 2015, using a SkyWatcher 10″, and a TeleVue Nagler zoom 3-6 mm. North is down.

Apparently there is some debate concerning the originator of the Bessel Ray: some suggest that it is associated with the nearby crater Menelaus (at the top of the sketch), others that it is part of the extensive ray system emanating from Tycho, far down south.

In an image from the Galileo spacecraft, the ray systems of Copernicus (left), Kepler (far left), Proclus (right)  and Tycho (bottom) are prominent. Mare Serenitatis, with the Bessel Ray, can be seen near the center. Judging from the image the Bessel Ray seems to connect both with Menelaus (the bright spot on the southern shore of the mare) and with Tycho. I am not sure what to make of it, but if think I put my money on Tycho. 


C/2014 Q2 (Lovejoy)

Discovered by Terry Lovejoy on 17 August 2014, comet C/2014 Q2 (Lovejoy) put on quite some show this spring. I had the opportunity to observe it on several occasions, using my 7×50 binos for the reports to COBS, and my scopes for the sketches.

The first sketch was made on 11 January. At the time the comet was just about visible naked eye and with the binos I estimated the magnitude to 4.5. There was no sign of the tail in the binos, but with the 16″ I saw hints of it. The tail was to elusive to put down in the sketch, so I just indicated my impressions with some dashes. When I later checked the observation at the laptop, it turned out that I had been spot on.

11 jan
Sketched 11 January 2015, UT 19:00 , using GSO 16″, Baader Asperic 31 mm (FOV 74′). North is up.

The second sketch was made two days later on 13 January. The comet now seemed considerably brighter, and with the binos I estimated the magnitude to 3.8. The tail was a difficult catch with the binos (at ZLM 5.5), but I eventually put it down as 1°. Due to it’s position in the local sky, I had to use the more portable 10″ for the sketch. In the eyepiece the coma was bright and very pronounced. Even the tail popped out nicely from the background. I also suspected two secondary streams of the tail, marked by the dashes to the left, but I am not sure that they were genuine. As it turned out this became my best view of the comet.

13 jan
Sketched 13 January 2015, UT 18:30, using SkyWatcher 10″, Baader Hyperion 24 mm (FOV 81′). North is up.

During the second half of January I made a couple of observations with the binos, but I didn’t sketch it again until 9 February. Even if the comet now had dimmed considerably (4.8) it still stood out quite well. At the time the tail didn’t show in the binos, but was not to difficult to catch in the big scope.

9 feb
Sketched 9 February 2015, UT 21:00, using GSO 16″, Baader Aspheric 31 mm (FOV 74′). North is up.

The last sketch was made under substandard skies on 14 February. Now the comet had faded to magnitude 5.5. Due to some haze the tail was very difficult to observe. It seemed to have a more fan-like shape than during previous observations, but that might have been the effect of the poor sky quality (or faint field stars playing a trick on me).

14 feb
Sketched 14 February 2015, UT 20:15, using GSO 16″, Baader Asperic 31 mm (FOV 74′). North is up.

All in all I found C/2014 Q2 an entertaining companion during the few months I observed it. Not as forgiving as for example comet C/2011 L4 (PanSTARRS) of 2012, but still well worth the effort.