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Alphonsus, with Rimae Alphonsus on its floor (impact site of Ranger 9)

Lat: 13.38°S, Long: 2.9°W, Diam: 110.54 km, Depth: 2.73 km, Rükl: 44, Nectarian

external image normal_Alphonsus-Arzachel-09-14-06-53map-s371.jpg
Wes Higgins In this view, west is up and north to the right. Alphonsus is the large crater on the right. To its left is the similar, but smaller, Arzachel; and above them Alpetragius. Part of the southeastern floor of Ptolemaeus is also visible on the extreme lower right. On the floor of Alphonsus there are a number of IAU-named features. These include Rimae Alphonsus, Chang-Ngo and the presumed volcanoes Ravi, Monira, José and Soraya.


LPOD Photo Gallery Paolo R. LazzarottiLunar Orbiter Images Apollo ImagesKaguya HDTV
Ranger 9 - Camera A photographs
Ranger 9 - Camera B photographs
Ranger 9 - Camera P photographs

  • Apollo 16's orbital Fairchild-camera photograph AS16-M-0714 (Alphonsus/ Arzachel) is included in the book Full Moon (Plate 26). Research: Danny Caes
  • A bass-relief model of Alphonsus's central peak was once made by scientific sculptor R.Turner. A photograph of R.Turner and the sculpted central peak was printed on page 29 of the book Operatie Maan by the Dutch populariser Chriet Titulaer.- DannyCaes Dec 19, 2010


(LAC zone 77D3) LAC map Geologic map LM map
USGS Geologic Map of the Alphonsus Region of the Moon (I-599)
USGS Geologic Map of the Alphonsus GA region (I-586), with actual impact location of Ranger 9.


Alphonsus is an old complex impact crater with an isolated central peak and an interesting flat floor. Alphonsus is famous for the dark patches along the edges of the floor that are ash deposits from the contained small volcano pits. The network of rilles that inter-connect the dark halo craters are probably surface fractures over dikes that brought magma toward the surface. The rim of Alphonsus is cut by linear troughs made by flying ejecta coming from the formation of Imbrium impact basin. The ridge through the center of Alphonsus is probably also Imbrium ejecta. In the 1950s Russian observations suggested that gases were emitted from the central peak of Alphonsus. But the more recent discovery that the 2.0 km high peak is made of anorthosite, an ancient rock formed in the magma ocean, demonstrates that volcanic eruptions did not occur 50 years ago.
Chuck Wood, June 3, 2007


(IAU Directions) ALPHONSUS.--A large walled-plain, 83 miles in diameter, with a massive irregular border abutting on the S.S.W. side of Ptolemaeus, and rising at one place on the N.E. to a height of 7000 feet above the interior. The floor presents many features of interest. It includes a bright central peak, forming part of a longitudinal ridge, on either side of which runs a winding cleft, originating at a crater-row on the N. side of the interior. There is a third cleft on the N.E. side, and a fourth near the foot of the W. wall. There are also three peculiar dark areas within the circumvallation; two, some distance apart, abutting on the E. wall, and a third, triangular in shape, at the foot of the W. wall. The last-mentioned cleft traverses this patch. These dusky spots are easily recognised in good photographs of the moon.



Additional Information

  • IAU page: Alphonsus
  • Floor-fractured crater
  • Central peak composition: pure anorthosite (Tompkins & Pieters, 1999)
  • Depth data from Kurt Fisher database
      • Westfall, 2000: 2.73 km
      • Viscardy, 1985: 2.73 km
      • Cherrington, 1969: 3.2 km
  • Central peak height
  • Crater with the 4th largest number of transient lunar phenomena reports: 18; A.P.S. Crotts (2007).
  • Eleven small pyroclastic deposits (area = 8 to 79 km^2) associated with dark halo craters. This is not the largest extent of pyroclastic materials but it is probably the greatest clustering of discrete sources. Gaddis, L. (1999) Lunar Pyroclastic Volcanism Project.
  • The artificial impact-craterlet created by Ranger 9 (on the floor of Alphonsus) is described and depicted in NASA SP-362, Apollo over the Moon; A View from Orbit, Chapter 5: Craters (Part 2), Figure 123.
  • NASA has selected a small area on the floor of Alphonsus (near Ravi) as a Region of Interest for investigation in connection with its Constellation program of exploration.
  • Nikolai Kozyrev and the case for lunar volcanism.

Lunar Ellipse of Fire

The floor of Alphonsus is (or was?) number seven in the list of 12 localities in the Lunar Ellipse of Fire (see article from Farouk El-Baz in Sky and Telescope - June 1973).


  • Named for Alfonso X (November 23, 1221, Toledo, Spain – April 4, 1284, Seville, Spain), a Spanish monarch. As a writer and intellectual he gained considerable scientific fame based on his encouragement of astronomy and the Ptolemaic cosmology as known to him through the Arabs. His fame extends to the preparation of the Alfonsine tables, based on calculations of al-Zarqali Alzarquel.
  • Alphonsus D, southeast of Alphonsus itself, was called Dublier by Hugh Percy Wilkins and Paluzie-Borrell, but the IAU did not accept that name. Dublier was a contemporary Spanish astronomer.
  • According to V.A. Firsoff's book The Old Moon and the New (1969), one of the regions on the west rampart of Alphonsus was called Lake Titicaca by Whitaker (see page 152 of that book). Of course, "Lake Titicaca" is not an official I.A.U.-name, but it would be interesting to know which part of Alphonsus it was (the exact location of Whitaker's "Lake Titicaca"). Detection of name "Lake Titicaca": Danny Caes. By the way, see also the terrestrial Lake Titicaca.

LPOD Articles

A Long Line in a Clutter of Magnificence. Just Another Glorious Image Craters and Papers Micro-Topo Volcanic Craters on the Moon The Golden Triad New Observations of a Well-Known Area

LROC Articles

Alphonsus crater mantled floor fracture

Lunar 100

L47: Dark-halo eruptions on crater floor.


Named Featues -- Prev: Alpetragius -- Next: Rimae Alphonsus