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Ptolemaeus
	Ptolemaeus from Apollo 16. NASA photo.
Coordinates	9°12′S 1°48′W / 9.2°S 1.8°W
Diameter	154 km
Depth	2.4 km
Colongitude	3° at sunrise
Eponym	Claudius Ptolemaeus

Ptolemaeus is an ancient lunar impact crater close to the center of the near side, named for Claudius Ptolemy, the Greco-Roman writer, mathematician, astronomer, geographer and astrologer. It measures approximately 154 kilometers in diameter.^[1]

Description

To the south-southwest, 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 polygonal 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 side 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.

Satellite craters

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Ptolemaeus.

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.

Ptolemaeus A — See Ammonius.

References

^ "Ptolemaeus (lunar crater)". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.

Andersson, L. E.; Whitaker, E. A. (1982). NASA Catalogue of Lunar Nomenclature. NASA RP-1097.
Bussey, B.; Spudis, P. (2004). The Clementine Atlas of the Moon. New York: Cambridge University Press. ISBN 978-0-521-81528-4.
Cocks, Elijah E.; Cocks, Josiah C. (1995). Who's Who on the Moon: A Biographical Dictionary of Lunar Nomenclature. Tudor Publishers. ISBN 978-0-936389-27-1.
McDowell, Jonathan (July 15, 2007). "Lunar Nomenclature". Jonathan's Space Report. Retrieved 2007-10-24.
Menzel D. H.; Minnaert, M.; Levin, B.; Dollfus A.; Bell, B. (1971). "Report on Lunar Nomenclature by the Working Group of Commission 17 of the IAU". Space Science Reviews. 12 (2): 136–186. Bibcode:1971SSRv...12..136M. doi:10.1007/BF00171763. S2CID 122125855.
Moore, Patrick (2001). On the Moon. Sterling Publishing Co. ISBN 978-0-304-35469-6.
Price, Fred W. (1988). The Moon Observer's Handbook. Cambridge University Press. ISBN 978-0-521-33500-3.
Rükl, Antonín (1990). Atlas of the Moon. Kalmbach Books. ISBN 978-0-913135-17-4.
Webb, Rev. T. W. (1962). Celestial Objects for Common Telescopes (6th revised ed.). Dover. ISBN 978-0-486-20917-3.
Whitaker, Ewen A. (1999). Mapping and Naming the Moon. Cambridge University Press. ISBN 978-0-521-62248-6.
Wlasuk, Peter T. (2000). Observing the Moon. Springer. ISBN 978-1-85233-193-1.

External links

Ptolemaeus at The Moon Wiki
I-556 Ptolemaeus - USGS Geological Atlas of the Moon, 1966
Wood, Chuck (March 3, 2004). "Ptolemaic Sunset". Lunar Photo of the Day.
Wood, Chuck (March 4, 2004). "Ptolemaic Peak Heights". Lunar Photo of the Day.
Wood, Chuck (May 15, 2004). "The Golden Triad". Lunar Photo of the Day. Archived from the original on May 30, 2018. Retrieved September 3, 2017.
Wood, Chuck (August 12, 2004). "Ptolemy's Strange Floor". Lunar Photo of the Day.
Wood, Chuck (October 31, 2004). "Sunrise and Sunset on the Triade". Lunar Photo of the Day. Archived from the original on October 14, 2017. Retrieved October 14, 2017. - one of three craters making up a Triad - that includes Ptolemaeus
Wood, Chuck (April 8, 2005). "Cups & Saucers". Lunar Photo of the Day. Archived from the original on May 30, 2018. Retrieved September 3, 2017.
Wood, Chuck (2006-04-06). "Micro-Topo". Lunar Photo of the Day. Retrieved 2006-07-21.
Wood, Chuck (November 27, 2006). "A Long Line in a Clutter of Magnificence". Lunar Photo of the Day. Archived from the original on June 14, 2011.
NASA Astronomy Picture of the Day: Ptolemaeus, Alphonsus and Arzachel (9 February 2007)
Wood, Chuck (May 15, 2008). "Unfamiliar Territory". Lunar Photo of the Day.
Wood, Chuck (January 28, 2009). "Ramparts". Lunar Photo of the Day.
Wood, Chuck (September 4, 2014). "Nessie". Lunar Photo of the Day.