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Posidonius, with Rimae Posidonius on its floor, and Giner (Posidonius P) northwest of it

Lat: 31.89°N, Long: 29.96°E, Diam: 100.75 km, Depth: 1.37 km, Rükl: 14, Upper Imbrian

external image normal_posidonius2005-09-22a.jpg
Mario Weigand
Posidonius and the very curious system of rilles on its crackled floor (Rimae Posidonius). The bowl-shaped crater northwest of Posidonius was once called Giner by H.P.Wilkins and P.Moore (see their book The Moon). This crater is nowadays officially known as Posidonius P. The largest one of the bowl-shaped craters on the rim of Posidonius seems to have been called Hellene by F.C.Lamech. It is nowadays officially known as Posidonius J.


LPOD Photo Gallery Lunar Orbiter Images Apollo Images

  • Posidonius was also captured on Apollo 15's and Apollo 17's oblique north-looking FairchildMetric-Mapping photographs.
    • AS15-M-1522 is one of those frames, which shows Posidonius very near the curved horizon (the central and "uppermost" part of the horizon).
    • Research: Danny Caes.
  • Kaguya HDTV
  • LROC WAC Mosaic


LAC map (north half) LAC map (south half) Geologic map (north half) Geologic map (south half)
LM map (south half)

Description Elger

(IAU Directions) POSIDONIUS.--This magnificent ring-plain is justly regarded as one of the finest telescopic objects in the first quadrant. Its narrow bright wall with its serrated shadow, the conspicuous crater, the clefts and ridges and other details on the floor, together with the beautiful group of objects on the neighbouring plain, and the great Serpentine ridge on the W., never fail to excite the interest of the observer. The circumvallation, which is far from being perfectly regular, is about 62 miles in diameter, and, considering its size, is not remarkable for its altitude, as it nowhere exceeds 6,000 feet above the interior, which is depressed about 2,000 feet below the surrounding plain. Its continuity, especially on the W., is interrupted by gaps. On the N., the wall is notably deformed. It is broader and more regular on the E., where it includes a large longitudinal depression, and on the N.E. section stand two bright little ring-plains. On the floor, which shines with a glittering lustre, are the well-marked remains of a second ring, nearly concentric with the principal rampart, and separated from it by an interval of nine or ten miles. The most prominent object, however, is the bright crater a little W. of the centre. This is partially surrounded on the E. by three or four small bright mountains, through which runs in a meridional direction a rill-valley, not easily traced as a whole, except under a low sun. There is another cleft on the N.W. side of the interior, which is an apparent extension of part of the inner ring, a transverse rill-valley on the N., a fourth quasi rill on the N.E., and a fifth short cleft on the S. part of the floor. Between the principal crater and the S.W. wall are two smaller craters, which are easy objects. Beyond the border on the N., in addition to Daniell, are four conspicuous craters and many ridges.

Description Wikipedia


Additional Information

  • IAU page: Posidonius
  • Depth data from Kurt Fisher database
    • Pike, 1976: 1.37 km
    • Westfall, 2000: 1.37 km
    • Cherrington, 1969: 2.59 km
  • Central peak composition: A (Tompkins & Pieters, 1999)
  • The central peaks arranged in a ring have heights, starting from the northernmost and proceeding clockwise, of: 0.8 km, 0.3 km, 0.3 km, 0.4 km Sekiguchi, 1972. - fatastronomer
  • Posidonius Gamma, a bowl shaped high-albedo craterlet with bright nimbus around it, in Mare Serenitatis, at LON: 24.91, LAT 30.04, is also photographed by the LRO, see ACT-REACT Quick Map (add the mentioned coordinates!).- DannyCaes Jun 19, 2011
  • The mare ridge at Posidonius Gamma is a thermal anomaly feature, implying fresh boulders are exposed at the surface (Moore et al, 1980), unexpected for a ridge.
  • Is Posidonius Gamma's high-albedo ejectablanket of the same nature as those of Lassell D, Linné, and Werner D? (several dedicated observers of the moon reported changes of brightness in these small ejectablankets). - DannyCaes Aug 23, 2015
  • Satellite crater Posidonius B is on the ALPO list of bright ray craters.
  • Wonderful "illuminated ring" effect during local sunset, when the floor of Posidonius is pitch black, and it's rim still illuminated by the sun's light.(- DannyCaes Sep 20, 2008, observation 19-9-'08, 23.00 U.T., Orion-Skyquest Dobsonian).
  • TSI = 25, CPI = 30, FI = 25; MI =80 Smith and Sanchez, 1973

Mysterious obscurations on the floor of Posidonius?

  • Mysterious obscurations seem to have happened at the bowl-shaped craters Posidonius A and Posidonius C, both on the floor of Posidonius itself. See pages 352-355 in the Dutch book Op Ontdekking in het Maanland by A.J.M.Wanders (1949).


  • Named for Posidonius of Apameia (ca. 135 BCE - 51 BCE), a Greek Stoic philosopher, politician, astronomer, geographer, historian, and teacher. He was acclaimed as the greatest polymath of his age. None of his vast body of work can be read in its entirety today as it exists only in fragments.
  • This name was part of the original IAU nomenclature of Blagg and Müller. It first appeared on Riccioli's map, where it was spelled Possidonius (Whitaker, p. 214).
  • Posidonius P, a small crater to the northwest of Posidonius itself, was called Giner by Wilkins and Paluzie (see Wilkins and Moore), but the I.A.U. did not accept the name. Tomas Giner Galbis was a contemporary Spanish astronomer.
  • Posidonius J, another one of the small secondary craters, was once known as Héllène. This was one of Felix Chemla Lamèch's new names. Alas... the I.A.U. did not accept the name Héllène... Research: Ewen A. Whitaker and Danny Caes (August 2003; mail correspondence).
  • Ghost of Posidonius (a nickname from D.Caes for the more-or-less circle shaped arrangement of several wrinkle ridges southwest of Posidonius, on Mare Serenitatis) (this "ghost" was already discovered during the preceding century and was depicted on lunar map SLC-B3).

LROC Articles

Rimae Posidonius

LPOD Articles

Rille Finder Interlude A Perfect LPOD Image A Glorious Image A Rille that Doesn't Know What to do with Itself (feb 9, 2007) Grazing Magnification An Old Fault? A Rille that doesn't Know What to do with Itself (may 7, 2009) Rilleorama

Lunar 100

L20: Floor-fractured crater.


Named Featues -- Prev: Porter -- Next: Rimae Posidonius