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Ptolemaeus is an ancient lunar impact crater close to the center of the near side. To the south-southeast Ptolemaeus is joined to the rim of Alphonsus crater by a section of rugged, irregular terrain, and these form a prominent chain with Arzachel to the south. To the southeast is Albategnius crater and to the north is the smaller but well-defined Herschel crater.

The features of Ptolemaeus are highlighted when the sun is at low angles during the first and last quarter. During the full moon the sun is directly overhead and the crater contours become more difficult to discern.

The crater has a low, irregular outer rim that is heavily worn and impacted with multiple smaller craters. The rim has a discernable polygonal shape, although overall it remains circular. The largest of the peaks along the rim, designated Ptolemaeus Gamma (γ), has an altitude of 2.9km and is located along the northwest rim. The crater has no central peak, a lava-flooded floor, and lacks a ray system. Impact sites of this form are often classified as a "walled-plain", due to their resemblance to the maria.

The somewhat dark-hued floor of Ptolemaeus is notable for several "ghost" craters, formed when lava flow covers a pre-existing crater. These leave only a slight rise where the rim existed, and are difficult to detect except at low angles of sunlight. There are also multiple smaller craters across the floor surface, most notably Ammonius crater in the northeastern quadrant.

On either of this crater are a linear, irregular gashes in the lunar surface, forming valley-like features. These features are approximately parallel to each other and radiate from the direction of Mare Imbrium to the north-northwest.



The Southern Highlands.

















Edge of Mare Imbrium, Latin for "Sea of Showers" or "Sea of Rains", is a vast lunar mare (mahr'-ay) filling a basin on Earth's Moon. Mare Imbrium was created when lava flooded the giant crater formed when a very large object hit the moon long ago. The moon's maria (mahr'-ee-ah) (plural of mare) have fewer features than other areas of the moon because molten lava pooled in the craters and formed a relatively smooth surface. Mare Imbrium is not as flat as it was originally because later events have altered its surface.

With a diameter of 1123 km it is second only to Oceanus Procellarum in size among the maria, and it is the largest mare associated with an impact basin. Apollo 15 landed in the southwestern region of Mare Imbrium, near the Apennine Mountains.



Posidonius is a lunar impact crater that is located on the western edge of Mare Serenitatis, to the south of Lacus Somniorum. The Chacornac crater is attached to the southeast rim, and to the north is Daniell crater.

The rim of Posidonius is shallow and obscured, especially on the western edge, and the interior has been overlaid by a lava flow in the past. The crater ramparts can still be observed to the south and east of the crater rim, and to a lesser degree to the north.

There is a smaller, semi-circular rim of a concentric, flooded crater within the main rim, offset toward the eastern edge. There is no central peak, but the floor is hilly and laced with a rille system named the Rimae Posidonius. The floor is also slightly bulged due to the past lava uplift, which also likely produced the complex of rilles. The northeast rim is interrupted by the smaller crater 'Posidonius B'. Within the crater rim, offset just to the west of center is another smaller crater 'Posidonius A'.

On the Mare Serenitatis surface near Posidonius crater is a notable system of wrinkle-ridges that parallel the nearby shore. These are designated the Dorsa Smirnov. At the peak of these ridges is a small craterlet with a diameter of 2 km. This craterlet is surrounded by a patch of high-albedo material, and is an example of a lunar bright spot. This peak was formerly designated Posidonius Gamma (γ).

The Posidonius Gamma feature was first observed by the lunar cartographer Julius Schmidt in 1857. He noted the similarity to the bright patch surrounding Linné crater.


Aristarchus is a prominent lunar impact crater that lies in the northwest part of the Moon's near side. It is considered the brightest of the large formations on the lunar surface, with an albedo nearly double that of most lunar features. The feature is bright enough to be visible to the naked eye, and is dazzling in a large telescope. It is also readily identified when most of the lunar surface is illuminated by earthshine. The crater is located at the southeastern edge of the Aristarchus plateau, an elevated area that contains a number of volcanic features, such as sinuous rilles. This area is also noted for the large number of reported transient lunar phenomena, as well as recent emissions of radon gas as measured by the Lunar Prospector spacecraft.

Aristarchus was originally named by the Italian map maker Giovanni Riccioli.





Mons Hadley  is a massif is the northern portion of the Montes Apenninus, a range in the north hemisphere of the Moon. The selenographic coordinates of this peak are 26.5° N, 4.7° E. It has a height of 4.6 km and a maximum diameter of 25 km at the base.
To the south of this mount is a valley that served as the landing site for the Apollo 15 expedition. To the southwest of this same valley is the slightly smaller Mons Hadley Delta (δ) peak with a height of about 3.5 km. The coordinates of this peak are 25.8° N, 3.8° E. To the west of these peaks is the sinuous Rima Hadley rille.



Gassendi is a large lunar crater feature located at the northern edge of Mare Humorum. The formation has been inundated by lava during the formation of the mare, so only the rim and the multiple central peaks remain above the surface. The outer rim is worn and eroded, although it retains a generally circular form. A smaller crater 'Gassendi A' is intruding into the northern rim, and joins a rough uplift at the northwest part of the floor. The crater pair bears a curious resemblance to a diamond ring. In the southern part of the crater floor is a semi-circular ridge-like formation that is concentric with the outer rim. It is in the southern part where the rim dips down to its lowest portion, and a gap appears at the most southern point. The rim varies in height from as little as 200 meters to as high as 2.5 kilometers above the surface. The floor has numerous hummocks and rough spots. There is also a system of rilles that criss-cross the floor, named the Rimae Gassendi.



Langrenus is a prominent impact crater located near the eastern lunar limb. The feature is circular in shape, but appears oblong due to foreshortening. It lies on the eastern shore of the Mare Fecunditatis. To the south is the overlapping crater pair Vendelinus and the smaller Lamé.The inner wall of Langrenus is wide and irregularly terraced, with an average width of about 20 kilometers. The outer ramparts are irregular and hilly, and there is a bright, fragmented ray system spread across the maria to the west. The interior of the crater has a higher albedo than the surroundings, so the crater stands out prominently when the sun is overhead. The crater floor is covered by many boulders, and is slightly irregular in the northwest half. The central peaks rise about a kilometer above the floor, and a peak on the eastern rim ascends to an altitude of 3 km.
During the Apollo 8 mission, Astronaut James Lovell described Langrenus as, "quite a huge crater; it's got a central cone to it. The walls of the crater are terraced, about six or seven terraces on the way down."
In the past this crater has not been noted as a site for observing transient lunar phenomenon. However on December 30, 1992, Audouin Dollfus of the Observatoire de Paris observed a series of glows on the floor of this crater using the one-meter telescope. These glows changed form with time, and Professor Dollfus expressed the belief that this was likely a gaseous emission. The cracked floor of the crater may have been the source of the gas.




Fra Mauro is the worn remnant of a walled lunar plain. It is part of the surrounding Fra Mauro formation, being located to the northeast of Mare Cognitum and southeast of Mare Insularum. Attached to the southern rim are the co-joined Bonpland and Parry craters, which intrude into the formation forming inward-bulging walls. The surviving rim of Fra Mauro is heavily worn, with incisions from past impacts and openings in the north and east walls. The rim is the most prominent in the southeast, where it shares a wall with Parry. The remainder consists of little more than low, irregular ridges. The maximum elevation of the outer rim is 0.7 km. The floor of this formation has been covered by basaltic-lava. This surface is almost divided by clefts running from the north and south rims. There is no central peak, although the tiny 'Fra Mauro E' crater lies at almost the mid-point of the formation. Just to the north of the walled plain is the landing site of the Apollo 14 mission. The crew sampled breccia that had been deposited here by the Imbrium basin-forming impact, and which partly covers the Fra Mauro crater. This rough debris blanket of ejecta is referred to as the "Fra Mauro Formation".



Montes Taurus is a rugged, jumbled mountainous region on the Moon. These peaks are located on a highland region to the east of the Mare Serenitatis, in the northeastern quadrant of the Moon's near side. The selenographic coordinates of this range are 28.4° N, 41.1° E, and they have a diameter of 172 km. Some of the peaks within the range achieve heights of 3.0 km. A number of craters lie embedded within this range. At the southwestern edge of the range is Römer crater, and Newcomb crater is located in the northeastern section. Several satellite craters also lie throughout the Montes Taurus. Apollo 17 landing site.



Hyginus is a small lunar caldera located at the east end of the Sinus Medii. The crater rim is split by a long, linear rille that branches to the northwest and to the east-southeast for a total length of 220 kilometers. The crater is deeper than the rille, and lies at the bend where they intersect. Together the Hyginus crater and Rima Hyginus form a distinctive and prominent feature in an otherwise flat surface. Smaller craterlets can also be discerned along the length of this rille, possibly caused by a collapse of an underlying structure. This is one of the few craters on the Moon that was not created as a result of an impact, and is instead believed to be volcanic in origin. It lacks the raised outer rim that is typical with impact craters.




Copernicus is a prominent lunar impact crater located in eastern Oceanus Procellarum. The crater Copernicus is estimated to be about 800 million years old, and typifies craters that formed during the Copernican period in that it has a prominent ray system. The circular rim has a discernible hexagonal form, with a terraced inner wall and a 30-km wide, sloping rampart that descends nearly a kilometer to the surrounding maria. There are three distinct terraces visible, and arc-shaped landslides due to slumping of the inner wall as the crater debris subsided. Most likely due to its recent formation, the crater floor has not been flooded by lava. The terrain along the bottom is hilly in the southern half while the north is relatively smooth. The central peaks consist of three isolated mountainous rises climbing as high as 1.2 km above the floor. These peaks are separated from each other by valleys, and they form a rough line along an east-west axis. Infrared observations of these peaks during the 1980s determined that they were primarily composed of the mafic form of Olivine.





Clavius is one of the largest crater formations on the Moon, and it is the third largest crater on the visible near side. It is located in the rugged southern highlands of the moon, to the south of the prominent Tycho crater. Due to the location of the crater toward the southern limb, the crater appears oblong due to foreshortening. Because of its great size, Clavius can be detected with the unaided eye. It appears as a prominent notch in the terminator about 1-2 days after the Moon reaches first quarter. The crater is one of the older formations on the lunar surface and was likely formed during the Nectarian period about 4 billion years ago. Despite its age, however, the crater is relatively well-preserved. It has a relatively low outer wall in comparison to their size, and it is heavily worn and pock-marked by craterlets. The rim does not significantly overlook the surrounding terrain, making this a "walled depression". The inner surface of the rim is hilly, notched, and varies in width, with the steepest portion in the south end. Overall the rim has been observed to have a somewhat polygonal outline. The floor of the crater forms a convex plain that is marked by some interesting crater impacts. The most notable of these is a curving chain of craters that begin with Rutherfurd in the south, then arc across the floor in a counterclockwise direction forming a sequence of ever diminishing diameters. From largest to smallest, these craters are designated Clavius D, C, N, J, and JA. This sequence of diminishing craters has proved a useful tool for amateur astronomers that want to test the resolution of their small telescopes.
The crater floor retains a diminished remnant of a central massif, which lies between Clavius C and N. The relative smoothness of the floor and the low size of the central peaks may indicate that the crater surface was formed some time after the original impact.



Messier is a relatively young lunar impact crater located on the Mare Fecunditatis. The crater has a discernable oblong shape that is not caused by foreshortening. The longer dimension is oriented in an east-west direction. Just to the west lies 'Messier A', a similar-sized crater with an oblong, doublet form. The longer dimension of this crater is oriented north-south, at right angles to Messier crater. This crater also has a curved bulge extending to the west. The interior of craters Messier and Messier A have a higher albedo than the surrounding maria. There is also a dark streak in the center of each crater. Two prominent, nearly linear rays extend westward from the rim of 'Messier A', continuing over 100 kilometers toward the east edge of Mare Fecunditatis. The maria about the craters is also lightly marked by rays from other craters.



Rheita is a lunar impact crater located in the southwestern sector of the moon. It lies to the northeast of Metius crater, and northwest of Young crater. The southwestern rim overlays the edge of Vallis Rheita, a long lunar valley strentching for over 200 kilometers on a line running northeast to southwest. At its widest the valley is 25 kilometers wide and a kilometer deep.
The rim of Rheita crater remains well-defined with a sharp lip and a terraced inner wall. The rim overlaps a slightly smaller crater to the east, and has a pair of small impact craters in the northern wall. The crater floor is flat and it has a central peak.



Schiller is an oddly-shaped lunar impact crater located in the southwest sector of the moon. To the east is the Bayer crater and to the southeast is Rost crater.
The rim of Schiller has an elongated shape that is amplified by its proximity to the lunar limb. The long axis lies along a line running northwest-southeast, with the wider girth located in the southeastern half. There is a slight bend in the elongation, with the concave side facing to the northeast. Observers have noted that Schiller appears to be a fusion of two or more craters. It bears a superficial resemblance to the footprint left by a shoe.
The crater rim is well-defined, with a terraced inner wall and a slight outer rampart. At the southeast end, a smaller crater is connected to Schiller by a wide valley. Most of the Schiller crater floor is flat, most likely due to lava flooding. There are some bright patches that are most clearly visible under a high sun angle. A double-ridge lies along the center of the northwest crater floor, forming a nearly linear formation that divides the floor in half.



Tycho is a prominent lunar impact crater located in the southern lunar highlands, named after Tycho Brahe. To the south is Street crater; to the east Pictet, and to the north-northeast is Sasserides crater. The surface around Tycho is replete with craters of various differing radii, many overlapping still older craters. Some of the smaller craters are secondary craters formed from larger chunks of ejecta from Tycho.
Tycho is a relatively young crater, with an estimated age of 108 million years, as estimated from samples of the crater rays recovered during the Apollo 17 mission. The crater is sharply defined and free of the wear that affects older craters. The interior has a high albedo that is prominent when the sun is overhead, and the crater is surrounded by a distinctive ray system forming long spokes that reach as long as 1,500 kilometers. Sections of these rays can be observed even when Tycho is only illuminated by earthlight.



Rupes Recta is a linear fault on the Moon, in the southeastern part of the Mare Nubium. The name is latin for "Straight Fault", although it is more commonly called the Straight Wall. This is the most well-known escarpment feature on the Moon, and is a popular target for amateur astronomers.
When the sun illuminates the feature at an oblique angle at about day 8 of the lunar orbit, the Rupes Recta casts a wide shadow that gives it the appearance of a steep cliff. The fault has a length of 110 km, a typical width of 2-3 km, and a height of 240-300 m. Thus although it appears to be a vertical cliff in the lunar surface, in actuality the grade of the slope is relatively shallow.



Sinus Iridum, the Rainbow Sea, is a plain of basaltic-lava that forms a northwestern extension to the Mare Imbrium. It is surrounded from the northeast to the southwest by the Montes Jura range. The protruding part of the range at the southwest end is named Promontorium Heraclides, while that at the northeast end is called Promontorium Laplace. This bay and the surrounding mountains is considered one of the most beautiful features on the Moon, and is a favorite among lunar observers.
Sinus Iridium does not contain any notable impact craters, but does include the satellite crater 'Heraclides E' in the south, 'Laplace A' along the eastern edge, and 'Bianchini G' in the north. The surface is level, but is marked by a number of wrinkle-ridges.



Vallis Alpes (latin for"Alpine Valley") is a spectacular lunar valley feature that bisects the Montes Alpes range. It extends 166 km from the Mare Imbrium basin, trending east-northeast to the edge of the Mare Frigoris. The valley is narrow at both ends and widens to a maximum width of about 10 km along the middle stretch. The selenographic coordinates of this feature are 48.5° N 3.2° E.
The valley floor is a flat, lava-flooded surface that is bisected by a slender, cleft-like rille. (This cleft is a challenging target for telescope observation from the Earth.) The sides of the valley rise from the floor to the surrounding highland terrain, a blocky, irregular surface. The southern face of the valley is straighter than the northern side, which is slightly bowed and uneven. The more rugged edges of the valley lie at the narrow west-southwest end that cuts through the mountain range. Most likely this valley is a graben that was subsequently flooded with magma.



Plato is the maria-surfaced remains of a lunar impact crater. It is located on the northeastern shore of the Mare Imbrium, at the western extremity of the Montes Alpes mountainous range. In the maria to the south are several rises collectively named the Montes Teneriffe. To the north lies the wide stretch of the Mare Frigoris. East of the crater, among the Montes Alpes, are several rilles collectively named the Rimae Plato.
The age of the Plato walled-plain is about 3 billion years; younger than the Mare Imbrium to the south. The rim is irregular with 2-km-tall jagged peaks that project prominent shadows across the crater floor when the sun is at a low angle. Sections of the inner wall display signs of past slumping, most notably a large triangular slide along the western side. The rim of Plato is circular, but from the Earth it appears oval due to foreshortening.
The flat floor of Plato crater has a relatively low albedo, making it appear dark in comparison to the surrounding rugged terrain. The floor is free of significant impact craters and lacks a central peak. However there are a few small craterlets scattered across the floor.
Plato has developed a reputation for various transient lunar phenomenon, including flashes of light, unusual color patterns, and areas of hazy visibility. These anomalies are likely a result of seeing conditions, combined with the effects of different illumination angles of the Sun.
The astronomer Johannes Hevelius originally called this feature the 'Greater Black Lake'.




Cleomedes is a prominent lunar crater located in the northeast part of the visible Moon, to the north of Mare Crisium. It is surrounded by rough ground with multiple crater impacts. The irregular Tralles crater is intruding into the northwest rim. To the east is the Delmotte crater. North of Cleomeses is a triple-crater formation with Burckhardt crater occupying the center.
The outer wall of this crater is heavily worn and eroded, especially along the southern part of the wall. The 'Cleomedes C' crater lies across the south-southwest rim. The crater floor is nearly flat, with a small central peak to the north of the mid-point, forming a linear ridge toward the north-northeast. There are several notable craterlets on the floor, including a pair of overlapping craters just inside the northwest rim.
A rille named the Rima Cleomedes crosses the northern floor, running southeast from the northwest rim. This rille branches in a fork after crossing the crater mid-line. Smaller clefts lie in the southeast part of the floor.









Fracastorius is the lava-flooded remnant of an ancient lunar impact crater located at the southern edge of Mare Nectaris. To the northwest of this formation lies the Beaumont crater, while to the northeast is Rosse.
The northern wall of this crater is missing, with only mounds appearing in the lunar mare to mark the outline. The lava that formed Mare Nectaris also invaded this crater, so the structure now forms a bay-like extension. The remainder of the rim is heavily worn and covered in lesser impact craters, leaving little of the original rim intact. The maximum elevation of the rim is 2.4 km. The most prominent of these craters is 'Fractastorius D', which overlays a portion of the western rim.
The Fracastorius crater has no central peak, but a long, slender rille runs across the middle of the floor in a generally east-west direction.



Albategnius is an ancient lunar impact crater located in the central highlands. It is named after the great muslim scientist Al-Battani. The level interior forms a "walled plain", surrounded by the high, terraced rim. The outer wall is somewhat hexagon-shaped, and has been heavily eroded with impacts, valleys and landslips. It attains a height above 4,000 meters along the northeast face. The rim is broken in the southwest by the smaller Klein crater.
Offset to the west of the crater mid-point is the central peak of Albategnius. This formation is designated Alpha (α) Albategnius. It is longer in extent in the north-south direction, extending for just under 20 kilometers, and has a width about half that. The peak rises to an altitude of roughly 1.5 km, and there is a tiny, relatively fresh crater at the top.
Albategnius is located to the south of the Hipparchus crater and to the east of Ptolemaeus and Alphonsus craters. The surface in this area is marked by a set of nearly parallel scars that form channels running roughly in a north-south line, bent slightly to the southeast.
The Albategnius crater is believed to have been featured prominently in an early sketch drawing by Galileo in his book Sidereus Nuncius published in 1610, appearing along the lunar terminator.