It is not like the Moon is ten days old only. This so-called “age” of the Moon is the time passed from the New Moon phase. And in that age 8-9 days there are numerous and unforgettable features on the Moon visible near the terminator line.

Ptolemaeus, Alphonsus, Arzachel, and small but exciting Aleptragius is a well-known configuration of craters. They are surrounded by other interesting features, and also contain some rilles and craterlets inside them, like for example Ammonius – the largest (8km) inside the Ptolemaeus. The Rupes Recta (Straight Wall is also nearby).

Ptolemaeus, Arzachel, Alphonsus
Ptolemaeus, Arzachel, Alphonsus

Rupes Recta is one of the most amazing features on the lunar surface. 120km long and 1000-1500 meters wide was described in older books as a cliff, but recent high-resolution photographies made with Sun at different altitudes confirm, that Straight Wall is actually a 30-45 degrees slope.

95km large impact crater Archimedes is the largest one in the image below. Its flat floor is filled with dark lava with a few tiny craterlets on the western side. South-east of Archimedes starts the largest mountain range on the near side, the Apennines. This is a 950km long and 100km wide collection of peaks, and the highest of them is Mount Huyghens at 5500m. The area between Archimedes and the Apennines is occupied by Palus Putredinis – a flat, square region containing traces of ejecta from Archimedes.

Archimedes and Montes Apenninus

About 100 million years ago a 10-km meteorite struck the Moon at high speed and gave birth to the crater Tycho. This crater is the center of the largest ray system on the lunar near side that are particularly conspicuous at Full Moon and are made of material thrown up by the impact and falling back to the Moon’s surface. Tycho is surrounded by many other craters, and the most prominent of them are Clavius, Longomontanus, and Blancacus. Clavius bears the marks of its great age and is one of the largest and most complex of lunar craters.

North-west of Clavius, there is a Longomontaus – an old, 145km wide crater with a flat floor filled with dark lava. And on the southwest slopes of Clavius lies Blancanus, a crater that is 105km wide and has a fantastic terraced wall 4km high. In the bottom right part of the image below lies Moretus – a magnificent, but a not well-known crater. Its outer slopes rise 2000 meters above the surrounding ground, and then fall 5000 meters down to the flat crater floor.

Tycho and Clavius
Tycho and Clavius

Palus Epidemiarum (Marsh of Epidemic) is an easily recognizable region filled with lava surrounded by many craters. One of them is Capuanus, an old, ruined crater about 60km wide with an asymmetric wall. Its shape resembles the bear paw with three claws. But the real observing treasures in this area are the rilles. Campanus Rille, Hesiodus Rille and of course Hippalus Rilles. The last one is three parallel concentric wrinkles about 250km long. Their shape suggests they are associated with the formation of the Mare Humorum when the lava went through a cooling phase. Above them, in the image, you may notice a Promontorium Kelvin – a lone mountains cape close to the 150km wide Rupes Kelvin.

Palus Epidemiarum
Palus Epidemiarum
Image technical data:

Date: 1-2 March, 2023
Location: Nieborowice, Poland
Telescope: Celestron SCT 8" with 2x Barlow
Camera: PlayerOne Saturn-C and ASI290MM
Mount: Celestron AVX
Exposure: each image is stack of 200 frames selected from 2000
Conditions: seeing medium