Plato Craterlets

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Plato Craterlets

Lat: 51.6°N, Long: 9.4°W, Rükl 3

external image Plato_Craterlet_diameters_LO4127.jpg
LPOD Photo Gallery: the white annotations are craterlet diameters (in kilometers) as measured on the Lunar Orbiter image with LTVT. Note that some features that look like they should be labeled, but aren't, are groupings of closely spaced smaller craterlets. For example, the prominent feature directly above the 1.76 km label on the left is two closely-spaced craterlets with diameters of 0.79 and 0.82 km -- together they are larger than some of the labeled single craterlets. For details regarding the unlabeled craterlets see the text file available under Additional Information.


LPOD Photo Gallery Lunar Orbiter Images


(LAC zone 12D3) LAC map Geologic map


The craterlets on the floor of Plato are one of the favorite targets for amateurs testing the detection limit of their telescopes.



Additional Information

  • Charles Wood has prepared a page comparing views of the Plato craterlets as seen (or imagined) by the classic lunar observers, some of whom thought the lack of agreement between their renderings was an indication of active volcanism and/or "fogs" periodically hiding parts of the floor: Plato Changes?.
  • An interesting discussion by BAA Lunar Section Director Walter Goodacre of early attempts to map the Plato craterlets (and streaks) can be found starting on page 94 of the Memoirs of the British Astronomical Association, Volume 20. The illustrations start with Plate I on page 129.
  • One of the final pre-space imagery efforts to map the Plato craterlets can be seen at History of the LAC maps.
  • The photographs found in most pre-space imagery lunar guides and atlases show Plato's floor as smooth and featureless, however this does not mean the craterlets could not be recorded photographically. For example, an undated Mount Wilson 100-inch telescope photo printed on page 92 of the December, 1959 Sky and Telscope accurately and fairly clearly shows the five largest (2.44-1.76 km in the index map shown above -- the 2.60 km crater being in shadow).
  • LTVT dot file: this LTVT dot file lists the positions and diameters of all circular Plato craterlets down to a diameter of 700 meters (and some beyond that). Since this is a simple text file, it can be used without the software; but with the software all craterlets over a specified threshold can be automatically plotted on a lunar image (as in Lunar Orbiter view shown above). The craters are numbered in order of decreasing size, so if an estimate has been made of the number of craterlets detected, one can simply read down the list to that number and thereby obtain a reasonable guess as to the diameter of the smallest craterlet detected. - JimMosher
    Note on accuracy: the measurements in this file were obtained in a single pass on a single photo. Although they are intended to represent the diameters at the peak of the crater rims, those rims are not defined with absolute precision on the Lunar Orbiter photos, nor are all the craterlets perfectly circular. As a result, repeated measurements, and measurements on other photos will give slightly different results. The accuracy of the present measurements was checked by re-measuring the four most prominent craters on the central floor (numbers 2-5 in the present list) on the same LO photo, on two other LO photos and on the USGS Warped Clementine Basemap (where positions and sizes are supposed to be represented with high accuracy). The following table gives the results including the average and standard deviation (statistical scatter) for the Lunar Orbiter measurements:

Craterlet #
Posted Value
Std Dev

  • The Clementine result for craterlet #2 is suspected of being erroneous due to a slight glitch apparent in the mosaicing, adding to the crater's apparent vertical height. The standard deviation of the repeated LO measurements appears to be about 0.04 km, meaning that about 1 value in 5 will have an error of +/-0.05 km and 1 in 80 will be off by +/-0.1 km. However, this is only the random error. The few Clementine HIRES images of the Plato craterlets that are available suggest the lower resolution images used here may be systematically exaggerating the diameters by as much as 0.1 km, but discrepancies of that magnitude have not generally been noted in comparing Lunar Orbiter and (better calibrated?) Apollo photos.- JimMosher
  • Pilz craterlet measurements: as an example of using this information to evaluate the detection limit of a specific amateur photo, this text file lists the results for an exceptionally fine photo of Plato taken by amateur Bob Pilz with an 8-inch reflector. Approximately 16 craterlets were successfully detected, giving a threshold diameter very slightly below 1 km. - JimMosher
  • Additional examples of cutting-edge photos of the Plato craterlets taken with a wide variety of apertures can be found on the LTVT Wiki.
  • The LTVT Wiki also has a page giving similar measurements of craterlet diameters in the vicinity of Rima Hadley.


  • None of the Plato craterlets have official IAU designations.
  • A number of schemes have been proposed for naming the craterlets. One such example is that of David Knisely, in which they are assigned letters. The classic observers tended to give them numbers. Since all these systems are unofficial, when amateurs say they have sighted "Plato craterlets A, B and C" there is some ambiguity as to what they might mean, depending on whose map they are referring to. It is also important not to confuse designations like these with the official IAU-named satellite features of Plato, none of which are located on the floor. - JimMosher

LPOD Articles

Impossibly High Standard A Hot Day on Plato Plato in My Dreams Platonic Nirvana Pushing the Envelope
(see Plato for additional links)