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Ptolemaeus (lunar crater)
Encyclopedia
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 the crater Alphonsus
by a section of rugged, irregular terrain, and these form a prominent chain with Arzachel
to the south. To the southeast is Albategnius
and to the north is the smaller but well-defined Herschel
.
The features of Ptolemaeus are highlighted when the Sun is at low angles during the first and last quarter. At 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 discernibly polygon
al shape, although overall it remains circular. The largest of the peaks along the rim, designated Ptolemaeus Gamma (γ), has an altitude of 2.9 km 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 walled plains, due to their resemblance to the maria.
The somewhat dark-hued floor of Ptolemaeus is notable for several ghost craters
, formed where lava has covered 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
in the northeastern quadrant.
On either of this crater are 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.
By convention these features are identified on lunar maps by placing the letter on the side of the crater mid-point that is closest to Ptolemaeus.
The following crater has been renamed by the IAU
.
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
close to the center of the near side. To the south-southeast Ptolemaeus is joined to the rim of the crater Alphonsus
Alphonsus (crater)
Alphonsus is an ancient impact crater on the Moon that dates from the immediate post-Nectarian era. It is located on the lunar highlands on the eastern end of Mare Nubium, west of the Imbrian Highlands, and slightly overlaps the crater Ptolemaeus to the north. The surface is broken and irregular...
by a section of rugged, irregular terrain, and these form a prominent chain with Arzachel
Arzachel (crater)
Arzachel is a relatively young lunar impact crater located in the highlands in the south-central part of the visible Moon, close to the zero meridian . It lies to the south of the crater Alphonsus, and together with Ptolemaeus further north the three form a prominent line of craters to the east of...
to the south. To the southeast is Albategnius
Albategnius (crater)
Albategnius is an ancient lunar impact crater located in the central highlands. It is named after the Muslim astronomer and 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...
and to the north is the smaller but well-defined Herschel
Herschel (lunar crater)
Herschel is a lunar impact crater located just to the north of the walled plain Ptolemaeus. Just to the north is the flooded crater Spörer, and due east lies the disintegrated crater Gyldén...
.
The features of Ptolemaeus are highlighted when the Sun is at low angles during the first and last quarter. At 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 discernibly polygon
Polygon
In geometry a polygon is a flat shape consisting of straight lines that are joined to form a closed chain orcircuit.A polygon is traditionally a plane figure that is bounded by a closed path, composed of a finite sequence of straight line segments...
al shape, although overall it remains circular. The largest of the peaks along the rim, designated Ptolemaeus Gamma (γ), has an altitude of 2.9 km and is located along the northwest rim. The crater has no central peak, a lava-flooded floor, and lacks a ray system
Ray system
A ray system comprises radial streaks of fine ejecta thrown out during the formation of an impact crater, looking a bit like many thin spokes coming from the hub of a wheel. The rays can extend for lengths up to several times the diameter of their originating crater, and are often accompanied by...
. Impact sites of this form are often classified as walled plains, due to their resemblance to the maria.
The somewhat dark-hued floor of Ptolemaeus is notable for several ghost craters
Palimpsest (planetary astronomy)
A palimpsest, in planetary astronomy, is an ancient crater on an icy moon of the outer Solar System whose relief has disappeared due to creep of the icy surface or subsequent cryovolcanic outpourings, leaving a circular albedo feature, perhaps with a "ghost" of a rim...
, formed where lava has covered 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
Ammonius (crater)
Ammonius is a bowl-shaped lunar impact crater with a slightly raised rim. It is located on the floor of the walled plain Ptolemaeus, about 30 kilometers northeast of the crater mid-point...
in the northeastern quadrant.
On either of this crater are 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
Mare Imbrium
Mare Imbrium, Latin for "Sea of Showers" or "Sea of Rains", is a vast lunar mare filling a basin on Earth's Moon and one of the larger craters in the Solar System. Mare Imbrium was created when lava flooded the giant crater formed when a very large object hit the Moon long ago...
to the north-northwest.
Satellite craters
| Ptolemaeus | Latitude | Longitude | Diameter |
|---|---|---|---|
| B | 7.9° S | 0.7° W | 17 km |
| C | 10.1° S | 3.3° W | 3 km |
| D | 8.2° S | 2.5° W | 4 km |
| E | 10.2° S | 4.5° W | 32 km |
| G | 7.1° S | 0.1° E | 7 km |
| H | 7.1° S | 5.4° W | 7 km |
| J | 9.6° S | 5.4° W | 5 km |
| K | 8.2° S | 4.6° W | 8 km |
| L | 8.8° S | 4.0° W | 4 km |
| M | 9.4° S | 3.4° W | 3 km |
| O | 7.2° S | 3.6° W | 5 km |
| P | 11.4° S | 3.2° W | 4 km |
| R | 6.7° S | 1.2° W | 6 km |
| S | 10.5° S | 0.5° W | 4 km |
| T | 7.5° S | 0.0° E | 7 km |
| W | 9.1° S | 1.4° E | 4 km |
| X | 10.9° S | 0.3° E | 4 km |
| Y | 9.3° S | 0.7° E | 6 km |
The following crater has been renamed by the IAU
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
.
- Ptolemaeus A — See AmmoniusAmmonius (crater)Ammonius is a bowl-shaped lunar impact crater with a slightly raised rim. It is located on the floor of the walled plain Ptolemaeus, about 30 kilometers northeast of the crater mid-point...
.