Our nearest celestial neighbour, the Moon, is full of interesting features and is easy to observe with even a small telescope. Here is the latest report from Moon observer extrordinaire Harry Roberts of the Sydney City Skywatchers:
Lunar mountains are strange creatures. On Earth mountain building is often the result of collisions between continental plates, the Himalayas being the best example. Indeed, if India hadn’t broken free of Antarctica and “hurtled” northwards to impact the super-continent Eurasia, there would be no Himalayas, no south polar cap, and the southern hemisphere would be uninhabitably hot. Amazing!
Lunar mountain building is rather different; it is largely the result of gigantic cratering impacts. What are the tallest mountains on the Moon? The Leibnitz Mountains that rim the lunar south pole were created by the largest impact we know of (anywhere), the South Pole-Aitken event, that left an enormous divot in the lunar far-side close to the south pole. The tallest peaks of this range have not been named (but have been numbered), and they exceed 5 km in height.
Of the more familiar Apennines, that partly ring the Mare Imbrium impact basin, Mons Bradley seems to be highest at 4.2 km. The seldom seen Mare Orientale basin on the Moon’s SW limb probably holds the record, with the Montes Rook at 6km high, though there seem not to be any named peaks amongst them; so the Rooks are the highest lunar mountains.
More easily located than the Rook’s or Leibnitz’ is Mons Penck that can be found just west of giant crater Theophilus Penck seems to be an isolated bit of the crater rim formed by the Mare Nectaris impact. Not much of this ancient impact rim remains; what does is called the Rupes Altai (the Altai Scarp) and it shows up dramatically on a five day old Moon. Mons Penck is 4 km high.
At 7:50 am (local) on Feb. 8 I had a nice view of this lunar mountain under “evening” lighting, with the terminator only 3 or 4 degrees east of the mountain. Although dotted in the figure, both giant craters Theophilus and Cyrillus were filled with shadow, and only their western rims were lit.
Mons Penck did not look like it usually does: the low angle lighting showed four short ridges that must form the top of the mountain, though it usually seems flat-topped. The 4km high peak threw a long shadow eastwards for about 60 km, in good agreement with the 4º angle of illumination.
Several low parallel ridges, probably impact debris from both Cyrillus and Theophilus, lay across the site. The linear crests of Penck almost attached to the high scarps that ran northwards from crater Kant; probably also part of the Altai Scarp. Kant was entirely shadow-filled, but crater Ibn Rushd showed a little inner wall and floor detail; presumably it has lower walls than fresher Kant. The dark area between Penck and Kant is actually a remnant crater called Kant E, an impact that probably helped to almost sever Mons Penck from the Altai Scarp.
A thin ray of light in the shadows east of Penck is probably sunlight flowing through the gap in the eastern-most ridge on the top of Mons Penck.
From the shadows cast by the ridges north of Kant we can see that they are about 3 km high. And a short double ridge about 50 km north of Kant casts a shadow almost as long as Penck itself: this too is presumably an isolated bit of the tilted scarp left by the Nectaris impact.
Penck: Albrecht, 1858 – 1945, German geographer. The name author is unknown. Mountain massif, height 4000 m, diameter 30 km.
Kant: Immanuel, 1724 – 1804, German philosopher, author of nebular hypothesis of the formation of the solar system. Crater 32 km dia. 3 km deep.
Ibn Rushd, Averroes, 1126 – 1198, Arabian philosopher, physician and lawyer at Spanish Muslin court. Crater, 33 km dia.
Search for isolated Penck, it’s one of the highest of the easily seen peaks on “our” side of the Moon.