Mare Orientale

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Orientale Basin

(unofficial name; official IAU feature name for central 327 km of mare: Mare Orientale)

Lat: 19.4°S, Long: 92.8°W, Main ring diam: 930 km, Basin depth: 6.04 km, Rükl: 50 & VII (farside)

external image normal_Mare%20Orientale%20lo4_m187.jpgexternal image normal_mareorientale20050101_0225_lazz.jpg
Left: Lunar Orbiter IV image 187M The IAU's Mare Orientale is the dark pool at the center of image, surrounded by the rings of the impact basin.
Right: Paolo Lazzarotti The dark ponds in this Earth-based view are Lacus Autumni (figure-8 shape near top) and Lacus Veris (snaky shape paralleling limb), neither very conspicuous in the Lunar Orbiter view. A thin sliver of the dark floor of Mare Orientale is visible along the limb at the bottom. See the Feb. 19, 2005 LPOD for an annotated version of this image.


LPOD Photo Gallery Lunar Orbiter Images Apollo Images Zond Images

  • Photographed in color at a high sun angle by the Galileo spacecraft in 1990.
  • A fine print from Lunar Orbiter IV image 187M (see above) was included on pages 210-211 of the article The Moon by Kenneth F. Weaver (National Geographic, February, 1969).
  • Strange to say, during the mission of Apollo 17 in december 1972, Mare Orientale was photographed in earthlight, when the lunar sunrise-terminator was still too eastward. These earthlight photographs are included in Apollo 17's Magazines 158-WW and 161-ZZ (35mm NIKON B&W photographs), see: Sheet 8 of A17's Index Maps. Some of those photographs were reproduced in the Apollo 17 Preliminary Science Report.
  • Frame 1 of Zond 8's spectacular photographs of the Mare Orientale region and gibbous Earth in the distance could be the "Russian equivalent" of William Anders's well-known photograph of the Earth above the lunar horizon (made during the mission of Apollo 8).
  • Research additional Lunar Orbiter, Apollo, and Zond photographs: Danny Caes
  • LROC mosaic.


(LAC zone 108B2) In USGS Digital Atlas mapped on LAC-90 PDF, LAC-73 PDF (not yet available), LAC-108 PDF, and LAC-91 PDF (not yet available). For an overview see Farside PDF. See also the older LMP-1 and LMP-2. LRO LOLA Topo Map (See 4.16.2010)

Basin Classification

(description of terms and most numeric basin data from Wood, C.A. (2004) Impact Basin Database)
Certainty of Existence
Wilhelms Age Group
Ring Diameters
Mare Thickness
320, 480, 620, 930, 1300, 1900 km
0.6-0.7 km
Yes; +18 mG gravity anomaly



Mare Orientale

Additional Information

  • Mare area of 69,000 km^2 according to measurements by Jim Whitford-Stark.
  • Western rim is estimated to be +6 km higher than the average (1738 km) lunar radius, and the floor of the Maunder crater is -5 km (below the avergae radius)
  • As might be expected from its selenographic longitude, the dark floor of Mare Orientale is visible from Earth under favorable conditions.


The IAU feature name means "Eastern Sea".
  • Named by Franz circa 1906 (Whitaker: Mapping and Naming the Moon, p. 225; Baum & Whitaker, p. 132).
  • Although apparently known to Blagg, Franz' name Mare Orientale was not included in the original IAU nomenclature of Blagg and Müller because its center is beyond 90 degrees longitude (Baum & Whitaker, p. 132).
  • The original 1935 IAU nomenclature of Named Lunar Formations did include the names Cordillera Mts and Rook Mts for certain features in the two most prominent basin rings visible from Earth at favorable libration, as well as for several dark mare areas: Mare Autumnae, Mare Veris, and Mare Aestatis and Mare Hiemis (a discontinued name for the dark floor of Schlüter) -- names also given by Franz (Baum & Whitaker, p. 132).
  • Named Mare X by H. P. Wilkins (who was apparently unacquainted with Franz' map) in 1938 (JBAA 48, page 80). Franz' name was recalled by T. L. MacDonald on page 270.
  • According to Baum & Whitaker (p. 134), the name Mare Orientale for the dark pool in the center of the present feature was "reinstated" in Kuiper's Photographic Lunar Atlas of 1960, although this is not mentioned in the table of corrections which was approved by the IAU in 1961. Nor is it mentioned in the revisions of limb nomenclature approved in connection with the Rectified Lunar Atlas in 1964, the approval date mentioned in the on-line IAU Planetary Gazetteer.
  • By whatever path Mare Orientale came to be an official IAU-approved name, the impact basin is named after it.
  • The revelation of the detailed appearance of the basin afforded by the Lunar Orbiter views stimulated much discussion about possible revisions in the IAU nomenclature for the entire area. G.P. Kuiper proposed renaming the entire basin Mare Annulatum (Ringed Sea). Other names under consideration included Lacus Pacificus ("Mare Pacificus" according to Whitaker) for the inner mare (Orientale), and Annulus Concordiae for the area between the Rook and Cordillera mountains. The final resolution seems to be embodied in a July 15, 1969 memo written by IAU Lunar Nomenclature Working Group chairman Donald Menzel:

  • "We have agreed that the central part of the great formation should retain the name Mare Orientale. We have agreed to change the names of Mare Veris and Mare Autumni to Lacus Veris and Lacus Autumni. Mare Aestatis becomes Lacus Aestatis. We define Montes Rook as applying to the circular mountains bordering Mare Orientale. We recognize that this border is not entirely complete, but it is clearly part of the same basic system and therefore deserves the same name. The same applies to Montes Cordillera, or the outer boundary of the same formation. These apply to the whole ring."

  • According to Baum and Whitaker (p. 134) "At the 1970 IAU convention in Brighton, these proposals were passed without further dissent." However, in fact only the renaming of the three small mare to "lacus" is mentioned there.
  • The IAU diameter of 327 km for Mare Orientale refers to the inner mare only. The unofficial name Mare Pacificus, mentioned in the preceding memo, has also been used, perhaps more commonly, to describe a prominent 175 km ash ring straddling the Rook and Cordillera rings in the southwest. That feature is on the terminator, and hence hard to see in the Lunar Orbiter image at the top of this page. - JimMosher
  • Geologists have added many more informal names for features within the impact basin (see, for example, Head, 1974 and Spudis et al., 1984), including such non-IAU-defined terms as the Inner and Outer Rook Rings/Mountains, the Maunder Formation, the Montes Rook Formation and the Hevelius Formation.
  • Somewhere south of Mare Orientale (northeast of Lagrange and Wilkins's Fresa) was Wilkins's and Paluzie-Borrell's crater called Juan, a name the I.A.U. did not accept. Juan (Jorge Juan Y Santacilia) was a Spanish geographer (1713-1773). (The Moon by H.P. Wilkins and P. Moore)

LROC Articles

LPOD Articles

Lunar 100

  • L80: Youngest large impact basin.