South Pole 90°S

The Moon's South Pole lies west of the barely 70-km crater Malapert (84.9°S, 12.9°E) – but slightly farther south. The next crater, lying to the west is Cabeus (84.9°S, 35.5°W), just about 100 km in diameter. The South Pole itself is difficult for even experienced lunar observers to locate, because it lies in an area that is saturated with craters, and the lighting and shadows create a chaotic appearance. Observation of the South Pole therefore requires optimum libration angles.

Moretus 70.6°S, 5.8°W

Gruemberger 66.9°S, 10.0°W

Moretus is a relatively young crater, 110 km in diamater, conspicuously terraced inner crater walls and a large, pyramid-shaped central mountain. It undoubtedly was created in the Eratosthenian period on the lunar timescale. It is a magnificent sight under favourable libration conditions in both large and small telescopes.

In stark contrast to Moretus is the significantly older, neighbouring crater Gruemberger, lying directly to the northwest, and which, with a diameter of 94 km, is of a similar size to Moretus. It is obvious from its heavily eroded crater wall that it is distinctly older. The crater Gruemberger A (20 km) lies on the crater's floor.

Curtius 67.2°S, 4.4°E

A crater, 95 km in diameter, with an eccentrically placed central peak, which lies northeast of Moretus. Smaller, later impacts have been superimposed on the crater wall in the south and the east. The crater's floor appears smooth and level.

Copernicus 9.7°N, 20.1°W

Copernicus is perhaps the most impressive example of a young, large complex crater, and which was formed about 800 million years ago. It lies between the southern side of Mare Imbrium and the northern portion of Mare Insularum, which has no distinct boundaries and merges into Oceanus Procellarum and Mare Nubium.

Copernicus has a diameter of 93 km and distinctly terraced inner crater walls, which tower 3.7 km above the crater's floor. A group of central mountains reaches up to heights of 1.2 km above the floor. The height of the outer ramparts amounts to only about 900 m. The southern portion of the crater's floor is saturated with a vast number of small hills, but the northern portion, by contrast, seems extremely smooth, level and structureless. It has probably been flooded by lava. The ratio of its depth to diameter of 1:25 (known as Schröter's Rule) corresponds more closely to that of a flat plate, rather than to the section of a bowl or funnel. When the Moon's age is about 9 to 10 days, a small lunar dome becomes visible about 90 km west of Copernicus. A large number of smaller secondary craters, crater pits and depressions lie in the terrain to the northeast of Copernicus. They were created by secondary impacts. A bright, extensive and very complex ray system becomes visible around the crater under high solar illumination.

Tycho 43.4°S, 11.1°W

Tycho is, with Clavius, undoubtedly the most prominent crater in the southern highlands. Its outer diameter amounts to 102 km and the inner crater wall measures about 85 km in diameter. It exhibits marked terraces on its interior walls and a complex central peak, which appears, from Earth, angular, steep and furrowed. The crater's walls reach a height of 4.8 km above the floor and the central peak towers 2.3 km above that floor.

Under high illumination, Tycho exhibits the largest and brightest of all ray systems. Tycho is certainly one of the youngest lunar craters, probably created only about 100 million years ago. Portions of the ray system may be traced over a distance of 1800 km. The most conspicuous and brightest rays stretch towards the east (Stöfler), southwest (Longomontanus, Clavius) and northwest (Kies, Bullialdus). The ray system is so bright that it is even visible by earthshine. Shortly after First Quarter, Tycho appears like a black chasm, surrounded by thick walls.

Under grazing illumination it becomes obvious that the crater is surrounded by a ring zone of dark material with a diameter of about 150 km. It consists of lunar crust that was melted by the energy of the impact and has subsequently solified.

Vallis Rheita 42.5°S, 51.5°E

Vallis Rheita is a linear valley, approximately 450 km long (similar to Vallis Snellius). At its widest points it reaches a width of about 30 km. It consists of a string of numerous, partially overlapping craters. It is oriented directly towards the centre of the Nectaris Basin and it is suggested that it may have arisen from secondary events following the Nectaris impact.

The crater chain begins northwest of the crater Rheita, crosses the crater Young (71 km, 41.5°S, 50.9°E), then the crater Mallet (58 km, 45.5°S, 54.2°E) and ends southeast of the crater Reimarus (48 km, 47.7°S, 60.3°E).

Rheita 37.1°S, 47.2°E

Rheita is a prominent crater, 70 km in diameter and with an eccentrically placed central peak, and lies northeast of Metius. Vallis Rheita runs past the crater's southern wall. Slightly farther north lies the crater Rheita E, which, with its measurements of 66 × 30 km, exhibits a very elongated shape. It consists of at least three overlapping individual craters, which probably (like Schiller) gained its current form through a later impact.

If the position of Janssen, Fabricius, Metius, Rheita and Rheita E is examined at a large scale, then it appears that they all lie on a nearly straight line. It is conceivable that their formation, nearly simultaneously, may be traced back to a very large asteroid that broke apart shortly before the impact.

Rima Bradley 23.8°N, 1.2°W

A conspicuous, 3 km wide straight rille running parallel to the Apennines, 130 km long. It undoubtedly marks a fracture zone at the foot of the Apennines.

Rimae Fresnel 28.0°N, 4.0°E

A complex system of linear rilles with a total length of about 90 km, lying northwest of Mons Hadley. The rille system ends near Cape Fresnel (the northern outlier of the Apennines). Visually, it appears to be an extension of Hadley Rille, but geologically they are separate rille systems.

Rima Hadley 25.0°N, 3.0°E

Rima Hadley is a sinuous rille with an overall length of about 80 km. It begins at the crater Bela, which, with a size of 2 × 11 km, under particular illumination, often appears in a telescope more like a sickle-shaped mountain ridge than a crater. The rille follows the foot of the Apennines, until it turns through 90° and ends at the foot of the mountain Mons Hadley Delta. The rille is a typical lava channel with a width of between 1 and 2 km and a depth of about 300 m. On 30 July 1971, Apollo 15 landed near the rille. The rille was thoroughly investigated, photographed and measured. A descent into the rille by the crew of Apollo 15 was forbidden by the flight directors because of the steep gradients involved.

Marco Polo 15.4°N, 2.0°W

The remnants of an elongated crater, measuring 21 × 28 km, lying behind the Apennine Front.

Mare Smythii

2.0°N, 87.0°E

Mare Smythii, ‘Smyth Sea’, named after a prominent, 19-century amateur observer, is a circular mare on the Moon's eastern limb and appears, because of limb foreshortening, to be highly elliptical. It covers an area of just about 105 000 km2, and a significant portion lies on the Moon's farside. Successful observation is only possible under favourable libration angles, but it then presents some interesting features. The outer wall of the basin rises above the lunar horizon, and various lava flows are visible inside it. In the north and south, in particular, there are unusually dark lava surfaces, which, in the south, are associated with the 55 km-diameter, FFC-crater Kiess. Mare Smythii is one of the youngest impact basins and its average depth is about 5 km below the general level of the surrounding surface.

Mare Marginis

12.0°N, 88.0°E

Mare Marginis, ‘Marginal Sea’, is an irregularly shaped lava area, 360 km across (about 62 000 km2). The mare has a north-south orientation and extends onto the Moon's farside.

Mare Marginis lies to the north of Mare Smythii. On the border between the mare lie the two craters Neper and Jansky. Neper (8.8°N, 84.5°E) is a large crater, 137 km in diameter. The floor of the crater is flooded by very dark lava and there is 1 2 a visible central peak. Jansky (8.5°N, 89.5°E) has a diameter of 73 km. Both craters are visible under favourable libration conditions.

Theophilus 11.4°S, 26.4°E

An impressive complex crater with a diameter of 110 km, which was created in the Eratosthenian period on the lunar timescale. The crater wall reaches a height of 4.4 km above the crater's floor and the huge, triple central peaks attain a height of 1.4 km above the floor. The crest of the rim is about 1.2 km above the surrounding terrain. Except for the western rim, the complete inner wall is marked by prominent terraces. At high magnifications they appear as linear, sectional landslips. The northwestern wall is broken by the small crater Theophilus B (8 km). The central peak is strongly split and has low foothills on the southern side. The crater floor appears smooth and flat and is filled with melted impact material, which is also emplaced right round outside the crater rim. In addition, large telescopes show a few crater pits on the floor.

Shortly after First Quarter, Theophilus appears bright and shows the beginnings of a ray system, which becomes more prominent with increasing solar altitude. About 100 km southeast lies Theophilus L, a small, circular crater 5 km in diameter, that has a halo of very dark material. It is a Dark Halo Crater.

Mädler 11.0°S, 29.8°E

Mädler is a very interesting crater, 27 km in diameter, lying east of Theophilus. It is the source of a very broad, fan shaped deposit of ejected material, which implies a grazing impact (as with Proclus). The fan extends in an easterly direction.

Close to the edge of the crater are two small craters: Copernicus H with a diameter of 5 km (to the southeast) and Gay-Lussac N, with a diameter of only 2 km (to the north). Both craters are surrounded by dark haloes and lie as if stamped into the Copernicus ejecta. Multispectral investigations show that the dark haloes consist of pulverized mare basalt, which was excavated from beneath the ejecta from Copernicus. Both craters are, admittedly, small, but they must be deep enough to have brought the basalt to the surface. They are included in the class of Dark Halo Craters. Two craters that arose similarly, and with dark haloes of mare basalt, lie southeast of Theophilus. Craters with dark haloes – like the bright ray systems – are best seen under high solar illumination. Because they are generally very small, it is advisable to use magnifications of 150 to 200× for visual observation.

Two smaller, overlapping craters, Fauth (12 km, 6.3°N, 20.1°W) and Fauth A (10 km) lie directly south of Copernicus. Fauth and Fauth A are most probably secondary craters, originating in the gigantic Imbrium impact. The two craters resemble a keyhole, and when taken together with Copernicus, the three craters serve as an indicator of the north-south direction of the lunar coordinate system.

Mare Tranquillitatis

8.5°N, 31.5°E

Mare Tranquillitatis, the ‘Sea of Tranquillity’, is an area of about 420 000 km2, slightly larger than Mare Serenitatis that lies to its north. Its size is comparable with the Black Sea on Earth. Like all the maria, Tranquillitatis is also the central, lava-flooded region of a considerably larger impact basin, and associated with a gravitational anomaly a mascon).

The enormous lava expanse of Mare Tranquillitatis was the target of some unmanned lunar probes: Ranger 6, Ranger 8 (1965, hard landings) and Surveyor 5 (1967, soft landing). Ranger 6 was a failure, because the cameras could not be activated shortly before impact. In 1969 the first manned lunar landing with Apollo 11 took place in the southern portion of the mare. The landing site of the landing module Eagle lay near to Ranger 8 and Surveyor 5, east of the craters Ritter and Sabine.

Mare Tranquillitatis offers a whole range of extremely interesting lunar formations for both small and large telescopes. The graduated brightness of the lava boundary southwest of the crater Carrel is remarkable, as is the lava boundary between Mare Serenitatis and Mare Tranquillitatis, north of the crater Plinius; the formation Lamont in the southwestern portion of Tranquillitatis is unique on the Moon's nearside; the lunar domes near Arago; the region around Cauchy and Jansen; and the broad rille systems on the western border of Tranquillitatis: Rimae Hypatia, Ritter, Sosigenes, and Maclear.

C. Herschel 34.5°N, 31.2°W

A small crater, only 13 km across, named after Caroline Herschel, the sister of William Herschel, who discovered the planet Uranus in 1781. Caroline Herschel was her brother's lifelong assistant and herself discovered eight comets.

Mons la Hire 27.8°N, 25.5°W

An isolated mountain massif occupying an area of about 11 × 25 km. It is probably the remnant of the former highlands (as was Mons Vinogradov) that was largely submerged by the Imbrium lava. The mountain peaks reach a height of 1.5 km above the lava plains.

Diophantus 27.6°N, 34.3°W

Delisle 29.9°N, 34.6°W

A pair of young craters lying directly north-south of one another, with sharp rims and diameters of 17 and 25 km, respectively. Delisle has an uneven crater floor with a half-destroyed craterlet, lying centrally on the floor.

Mons Delisle is an isolated remnant of the former highlands, lying southwest of Delisle, with a length of about 30 km. The southern portion of the mountain is rounded and higher, towards the north the ridge distinctly flattens out.

Samir (2 km) is a crater pit with a faint ray system under high solar illumination, and directly alongside lies the crater Louise. Diameter measurements for Louise vary between 800 m and 1.5 km. Both craters lie directly in the centre between Diophantus and Delisle.

Rosse 17.9°S, 35.0°E

A young, circular crater, diameter 12 km, lying in the southern area of Mare Nectaris. A bright ray of ejecta from the Tycho impact runs northwards from it (from southwest to northeast). Under high solar illumination, larger instruments show a group (a crater cluster) of very bright tiny secondary craters within the ray. Rosse is the only conspicuous crater on the monotonous lava expanse of the Nectaris Basin and therefore stands out all the more.

Fracastorius 21.5°S, 33.2°E

Fracastorius is a highlight for any aperture of telescope. It is a large complex crater of about 120 km in diameter, that is slightly oval in the north-south direction. Like a bay, the crater wall opens in the north onto the lava surface of Mare Nectaris, in a way that is morphologically similar to the craters Letronne (Mare Humorum) and Le Monnier (Mare Humorum). However, low remnants of the wall are still detectable in the north.

A small, nameless rille crosses the crater floor, almost exactly from west to east, and which splits into a ‘Y’ shape on the eastern side. It crosses the small crater Fracastorius M (4 km). The southern floor of the crater is saturated with a whole host of crater pits, but the northern floor is relatively flat and level. Well to the north is a small crater, surrounded by a bright halo of anorthositic crustal material.

Autolycus 30.7°N, 1.5°E

Aristillus 33.9°N, 1.2°E

A very conspicuous and prominent pair of craters in the Apennine region of Mare Imbrium. Under high solar illumination both craters exhibit ray systems. Autolycus, with a diameter of 39 km, has a very rough crater floor with a heavily eroded central peak. Aristillus has a diameter of 55 km. The inner walls of the crater are terraced and the central peak appears prominent above a level, smooth crater floor. The individual summits of the central mountain reach a height of up to 900 m above the floor. Particularly conspicuous is the broad annular zone of melted ejecta that is piled up outside the crater's wall. Directly north of Aristillus, this ejecta covers a submerged ghost crater, about 40 km in diameter, which may be seen only under grazing illumination.

Sinus Lunicus

32.0°N, 1.0°W

The Sinus Lunicus, ‘Bay of the Moon’, is a lava plain enclosed by two low ridges and lies between the craters Autolycus and Aristillus in the northeast and Archimedes in the southwest. In 1959, the Russian lunar probe Luna 2 made a hard landing on the lunar surface west of Autolycus. The region was officially named Sinus Lunicus by the IAU in 1970. Luna 2 was the first lunar probe to reach the Moon's surface. Its predecessor, Luna 1 missed the Moon by about 6000 km on 4 January 1959.

Secchi 2.4°N, 43.5°E

A smaller crater with a diameter of 22 km, with a wall that is broken in the north and south. The western crater wall adjoins the small and not very pronounced range of mountains, known as Montes Secchi (3.0°N, 43.0°E, length c. 50 km).

Rimae Secchi 1.0°N, 44.0°E

Rima Secchi is a difficult-to-observe rille system, c. 35 km long, lying south of the crater Secchi. At the northeastern end, the rille splits into the form of a ‘Y’. An aperture of at least 20 cm is needed for it to be observed.

Gutenberg 8.6°S, 41.2°E

A lava-flooded crater, 74 km in diameter. The eastern wall is broken by the similarly lava-flooded crater Gutenberg E (28 km). To its south lies Gutenberg C (45 km), which has completely destroyed the southern wall of Gutenberg itself. On the southwestern wall lies Gutenberg A (15 km). Within the crater a series of hills and the southern portion of Rimae Gutenberg are visible.

The rille system has a total length of c. 330 km. To the east lies the Rimae Goclenius rille system, which has an overall length of 240 km. Both systems consist of linear, largely parallel rilles, which are wide enough to be seen even with smaller telescopes. Each of the individual rilles consists of two parallel fault zones, with a sunken floor lying between them. They probably arose when the massive lava surface of Mare Fecunditatis sank under its own weight when it cooled.

Montes Teneriffe

48.0°N, 13.0°W

Montes Teneriffe are a loose group of mountain peaks, which, with a height of about 2.4 km are all about the same height, and so do not differ from the height of Mons Pico. The mountains Montes Teneriffe, Montes Recti, and the individual mountains Mons Piton and Mons Pico are probably the towering remnants of the otherwise submerged inner wall of the Imbrium Basin.

Montes Recti

48.0°N, 20.0°W

A linear range of mountains, running directly east-west for about 90 km, and with a width of about 20 km. The highest peaks reach a height of 1.8 km above the level of the lava of Mare Imbrium. They are part of the inner wall of the Imbrium Basin.

Mons Pico 46.0°N, 9.0°W

Mons Pico is an isolated mountain with an area at its base of 15 × 25 km and a height of 2.4 km. It lies exactly on the edge of ‘Ancient Newton’. The mountain was named by Johann Hieronyus Schröter (1745—1816) after Pico del Teide on Teneriffe, a peak that he compared to the mountain on the Moon.

When Mons Pico is observed under grazing illumination, the mountain casts a spectacular, pitch-black shadow, as much as 90 km long, on the surrounding lava surface, and gives the appearance of an extremely steep, towering peak. Because the Moon has no atmosphere whatsoever, sunlight is not scattered and this intensifies the shadow.

Mare Nubium 20.0°S, 15.0°W

Mare Nubium (‘Sea of Clouds’) is irregular, roughly round in shape, with no distinct boundaries anywhere, such as those found with other maria, typically in the form of sections of wall. It is possibly part of the enormous lava flow to which Mare Cognitum, Mare Insularum and parts of Oceanus Procellarum belong. It has a diameter of roughly 750 km and the lava covers an area of about 250 000 km2. Mare Nubium offers a multitude of interesting surface features for both visual and photographic observation.

Lubiniezky 17.8°S, 23.8°W

An almost completely lava-filled crater, 44 km in diameter, similar to Keis, lying northwest of Bullialdus. The southeastern crater wall is open to the lava surface of Mare Nubium. The maximum difference in height between the crater's wall and the floor amounts to just 770 m. Northwest of Lubiniezky lie the two craters Lubiniezky A and E. The former crater wall of Lubiniezky E (c. 40 km, 16.5°S, 27.2°W) has been practically completely submerged by lava, only a few individual peaks stick up above the surface of the lava.

Bullialdus 20.7°S, 22.2°W

A very conspicuous crater, 60 km in diameter, with terraced inner crater walls and a central mountain with multiple peaks. Melted ejecta material lies radially around the outside of the crater. It appears like a smaller version of the large crater Copernicus, but under high solar illumination shows no sign of a ray system, despite the fact that it must be relatively young.

Rupes Recta 22.1°S, 7.8°W

Rupes Recta – also known as the Straight Wall, Straight Scarp or Wall Beta – is a typical lunar undulation, an embankment. With grazing illumination it is a spectacular surface feature, even for observations with small telescopes. Lengths that are given vary between 110 km and 130 km, and the difference in height between the eastern and western sides amount to between 250 and 300 m, with a width of about 2.5 to 3 km. This gives a gradient of less than 10°, so Rupes Recta is rather a gentle slope and not – as the spectacular shadow might imply – a steep escarpment. The slope was probably created by a subsidence of the western side – the crater Birt side – of Mare Nubium, initiated by shock waves from the Imbrium impact and later altered and deformed by the Mare Nubium lava flows.

During the time around First Quarter, Rupes Recta is illuminated by the Sun at a low angle and casts a shadow that is easily visible even in small telescopes. A few days later, when the day/night border (the terminator) is about 20 to 30° away, the feature disappears and may only be made out in large telescopes. At the time of Last Quarter, Rupes Recta appears as a bright line, and a narrow rille (at right angles to Rupes Recta) becomes visible. North of Rupes Recta lies Promontorium Taenarium (19.0°S, 7.0°W).

Hipparchus 5.1°S, 5.2°E

Hipparchus is a giant, heavily ruined crater, with a diameter of 138 km and a depth of 3 km, which arose in the Pre-Nectarian period. The southeast crater wall is broken split by two deep, broad gaps. The northwestern wall of the crater is likewise largely destroyed, and exhibits wide gorges that are open towards Rima Réaumur (about 30 km long) and to Sinus Medii. Rima Réaumur encounters Rima Oppolzer at almost a right angle. Both are linear fracture zones, probably associated with the lava surface of Sinus Medii.

The floor of Hipparchus exhibits mountain peaks, small hills, crater pits, ghost craters and the 30-km, well-preserved, young crater Horrocks. The southwestern crater wall of Hipparchus is almost completely destroyed, and is covered with a group of both large and small craters.

The crater walls of Hipparchus generally consist of a series of holes, furrows, rilles, hills and ridges. The pattern that these features exhibit is radial to the centre of the Imbrium Basin. They are part of the Imbrium Sculpture and may be followed over a distance of more than 1000 km.

Albategnius 11.7°S, 4.3°E

Albategnius is a prominent, very conspicuous complex crater with a diameter of 114 km, an imposing central peak and a flat, smooth crater floor. The inner walls have been heavily eroded by landslides and intervening valleys, and is saturated with craterlets. The western crater wall is overlapped by the 44-km wide crater Klein. Under grazing illumination at sunrise (waxing Moon), numerous, very shallow, circular depressions are visible. Two of these lie directly to the east of the central peak, and two more to the south. The highest summit on the central peak has a pit that is about 1 km in diameter.

Lacus Mortis 45.0°N, 27.0°E

The ‘Sea of Death’ fills an extensively eroded large complex crater of about 150 km diameter, of which, fundamentally, only the western crater wall remains. The lava covers an area of c. 210 000 km2 and lies to the south of the eastern end of Mare Frigoris.

Mason 42.6°N, 30.5°E

Plana 42.2°N, 28.2°E

Lying south of Bürg is the overlapping pair of craters Mason and Plana (oriented east-west). Both craters are lava-flooded. Mason, with dimensions of 33 × 43 km, is a significantly elliptical crater. Plana has a central peak and a diameter of 44 km. Both craters seem partially ruined, and on both crater floors craterlets are visible in large telescopes.

Bürg 45.0°N, 28.2°E

Bürg is a prominent young crater (diameter 39 km) with a sharp-edged crater wall, that towers above the crater floor by about 2.2 km. The crater lies in the middle of a lava flow that was produced significantly earlier. Bürg has been dated to the Copernican period on the lunar timescale and in certainly one of the youngest of the larger craters on the nearside.

Bürg has a dominant central peak and terraced inner crater walls with many deep cracks and breaks. The ejecta from the impact lies in two masses to the north and – in a broad fan – to the south of the crater (somewhat similar to a mare wrinkle ridge).

Langrenus 8.9°S, 61.1°E

Langrenus is a very large and striking complex crater in the southwestern quadrant of the Moon. It has a diameter of 127 km, with 2.7 km-high, terraced inner crater walls, central peaks and a hilly crater floor. Under low solar illumination, the floor of the crater appears to have yellowish-brownish tints, in comparison with the neutral grey of the crater's surroundings. Langrenus has two conspicuous central peaks, which on old Moon maps were designated Langrenus alpha (the southern) and Langrenus beta. The southern crater wall is shaped rather like a triangular cape, and below it lie the craters Langrenus O and E, and Lohse (42 km, 13.7°S, 60.2°E).

Petavius 25.1°S, 60.4°E

Petavius is a giant complex crater with a diameter of 190 km. The inner crater walls are terraced and tower almost 3.3 km above the crater floor. Fairly central lies a large central, mountainous massif (south of which is the craterlet Petavius A).

On the floor of Petavius, a fracture zone (the main rille of Rimae Petavius) runs through the central massif. An additional segment begins on the western side of the central massif and runs farther west to the inner crater wall, and from there – less distinct – in both north and south directions, thus following the crater wall. These clefts and faults, together with the dark patches on the floor of the crater, indicate post-volcanic activity, long after the actual impact event.