- Wes Higgins' image
PLATO.--This beautiful walled-plain, 60 miles in diameter, with its bright border and dark steel-grey floor, has, from the time of Hevelius to the present, been one of the most familiar objects to lunar observers. In the rude maps of the seventeenth century it figures as the "Lacus Niger Major," an appellation which not inaptly describes its appearance under a high sun, when the sombre tone of its apparently smooth interior is in striking contrast to that of the isthmus on which the formation stands. It will repay observation under every phase, and though during the last thirty years no portion of the moon has been more diligently scrutinised than the floor; the neighbourhood includes a very great number of objects of every kind, which, not having received so much attention, will afford ample employment to the possessor of a good telescope during many lunations.
The border of Plato, varying in height from 3,000 to 4,000 feet above the interior, is crowned by several lofty peaks, the highest (7,400 feet) standing on the N. side of the curious little triangular formation on the W. wall. Those on the E., three in number, reckoning from N. to S., are respectively about 5,000, 6,000, and 7,000 feet in altitude above the floor. The circumvallation being very much broken and intersected by passes, exhibits many distinct breaches of continuity, especially on the S. There is a remarkable valley on the S.E., which, cutting through the border at a wide angle, suddenly turns towards the S.W., and descends the slope of the glacis in a more attenuated form. Another but shorter valley is traceable at sunrise on the E. On the N.E., the rampart is visibly dislocated, and the gap occupied by an intrusive mountain mass. This dislocation is not confined to the wall, but, under favourable conditions, may be traced across the floor to the broken S.W. border. It is probably a true "fault." On the N.W., the inner slope of the wall is very broad, and affords a fine example of a vast landslip.
The spots and faint light markings on the floor are of a particularly interesting character. During the years 1869 to 1871 they were systematically observed and discussed under the auspices of the Lunar Committee of the British Association. Among the forty or more spots recorded, six were found to be crater-cones. The remainder--or at least most of them--are extremely delicate objects, which vary in visibility in a way that is clearly independent of libration or solar altitude; and, what is also very suggestive, they are always found closely associated with the light markings,--standing either upon the surface of these features or close to their edges. Recent observations of these spots with a 13 inch telescope by Professor W.H. Pickering, under the exceptionally good conditions which prevail at Arequipa, Peru, have revived interest in the subject, for they tend to show that visible changes have taken place in the aspect of the principal crater-cones and of some of the other spots since they were so carefully and zealously scrutinised nearly a quarter of a century ago. The gradual darkening of the floor of Plato as the sun's altitude increases from 20 deg. till after full moon may be regarded as an established fact, though no feasible hypothesis has been advanced to account for it.
On the N.W. of Plato is a large bright crater, A; and, extending in a line from this towards the W., is a number of smaller rings, the whole group being well worth examination. On the N. there is a winding cleft, and some short crossed clefts in the rugged surface just beyond the foot of the wall, which I have seen with a 4 inch achromatic. The region on the E., imperfectly shown in the maps, includes much unrecorded detail. On the Mare Imbrium S. of Plato is a large area enclosed by low ridges, to which Schroter gave the name "Newton." It suggests the idea that it represents the ruin of a once imposing enclosure, of which the conspicuous mountain Pico formed a part.
- IAU page: Plato
- Depth data from Kurt Fisher database
- Pike, 1976: 2 km
- Westfall, 2000: 2 km
- Cherrington, 1969: 2.43 km
- Measurements of crater topography using Kaguya laser altimeter terrain profile graphs - LunarJim Sep 26, 2011
- Crater Depth: Measurements on 4 axes separated by 45 degrees.
- Zero reference level = Moon average radius.
- Average floor level (average of lowest levels on 4 axes) = -2.55 km
- Average rim height (average of 8 rim data points) = -0.87 km
- Average crater depth (average rim height to average floor level) = 1.68 km
- Deepest point on crater floor (from zero reference level) = -2.59 km
- Max. crater depth (highest point on rim to deepest point on crater floor) = 2.25 km
- West rim slope 13°, east rim slope 15° (Pohn, 1963)
- Plato is the crater with the second largest number of lunar transient phenomena reports: 40; A.P.S. Crotts (2007). (some the LTP reports refer to alleged changes in the pattern of craterlets on the floor, others to nothing more than the first/last touching of the curved floor by rays of sunlight streaming over low points in the rim at sunrise/sunset). - JimMosher)
- Pits on floor first reported by Gruithuisen by 1824; Johann Schröter had seen none (Sheehan and Dobbins, p 76).
- Attempts to catalog the pits by visual observation are documented by Walter Goodacre starting on page 94 of the Memoirs of the BAA (Vol. 20, Part 3), accompanied by numerous drawings starting with Plate 1.
- For a correct list of the pits and their sizes based on space imagery see Plato craterlets.
- Rim heights: as noted by Elger, the rim of Plato, like that of almost any crater of substantial size, is irregular in height. In Neison the peak Elger mentions on the west rim, casting the longest shadow at sunset, was called Plato Zeta. The three on the east rim, casting the three longest shadows at sunrise (also refered to by Elger) were, from south to north, Gamma, Delta and Epsilon. It should be noted that these are not necessarily the tallest peaks -- they are simply the ones best located to cast conspicuous shadows. The shadows in modern photos (as measured by LTVT) suggest the "Zeta" peak (on the west) rises about 2900 m above the crater floor. The three classic peaks on the east rise about 3200, 2600, and 1900 m. Hence, contrary to Elger, the Gamma peak appears to be a little taller than "Zeta", rather than the other way around. Also, there are actually secondary peaks between Gamma and Delta, and between Delta and Epsilon, both of which are taller than Epsilon, making the latter the fifth tallest peak on the east rim (not the third). The ups and downs of Plato's rim (including at positions not well situated to cast shadows) can perhaps best be visualized in a stereo view. In this view, as in Wes Higgins’ photo, the "Zeta" peak is particularly conspicuous, probably because it is more massive than the Gamma peak. It might be noted that in the System of Lunar Craters maps, once endorsed by the IAU, the meaning of Plato Zeta was apparently changed to refer to the large detached and sunken massif below the west wall. That massif is not responsible for the long shadows seen at sunset. The longest shadow at sunset comes from the peak above it in Wes Higgins’ photo. Also, the names "Plato Omega" and "Plato Phi" suggested in the historic Peaks of Plato LPOD referenced below should not be used. Those names both had well-defined meanings in the System of Lunar Craters and refered to completely different peaks near the perimeter of the ejecta blanket. Their locations are carefully indicated on LAC 12 from 1967. The rim heights given above are quite different from those (copied from LAC-12) mentioned in the LPOD, but are considered (at least by me) more reliable, because values in the range quoted here are obtained from a wide variety of photos at different sun angles. In addition to peaks, the lowest points on the rim are of equal interest. When combined with the peaks they give the impression that the west rim generally diminishes in height as one goes south, while the east rim generally increases in height (going in the same direction). To the north of the main peak on the west rim, the lowest shadow-casting point descends to within about 1400 m of the crater floor; but just to the south of the sunken massif, heights as low as 1100 m are encountered on the rim, followed almost immediately by a pair of peaks about 2000 m tall. On the east, the low points on the rim are about 1350 m above the floor to the north of the Epsilon peak, and 1700 m just to the north of the Gamma peak. Around Plato G there is a notch in the east rim which may well be the lowest point in that area, but its exact height is difficult to evaluate with the shadow technique, since the rim there is, itself, thrown into shadow by Plato G. There appear to be deep notches in the north-east and south rims as well, but they are not situated in positions suitable for evaluation using the shadow method (for them, see the stereo view). - JimMosher
- Height of Plato's floor: the most reliable evidence would seem to be the data from the Clementine LIDAR (altimeter) experiment, which can be plotted with LTVT. Those data suggest that the floor of Plato is is about 500 m higher than the plains of Mare Imbrium, to the south; and perhaps 100 m above Mare Frigoris, to the north. Plato's floor appears to be level (that is, it follows the Moon's radius of curvature) within the accuracy of the LIDAR data. - JimMosher
- The notion that Plato's floor darkens in an absolute sense as the Sun rises rises over it, which Elger takes as an "an established fact," seems to have originated with British amateur W. R. Birt in about 1871; and was repeated not only by Elger (1895), but also by Neison (1876) and Goodacre (1931). A little before 1900, American astronomer W. H. Pickering reported similar areas of darkening in Alphonsus, Riccioli and Atlas. Like Birt, Pickering assumed the darkening was evidence of physical change -- in Pickering's mind, most probably a monthly ebb and flow of lunar vegetation. As photometric measurements in the mid 20th century demonstrated, the darkening is simply an illusion: all surface areas brighten with the approach of Full Moon, but mare areas -- like the floor of Plato -- brighten less strongly, making them appear darker by contrast. (see Ashbrook, 1959) - JimMosher
- Named for Plato (428/427 BC – 348/347 BC), an ancient Greek philosopher.
- Van Langren called it Lacus Panciroli.
- Johannes Hevelius designated this crater Lacus Niger Major (the "Great Dark Lake").
- The name Plato was suggested Riccioli.
- By the time Mary Blagg's Collated List was prepared, all authorities consulted used Riccioli's suggestion, and it was adopted in that form into the original IAU nomenclature of Named Lunar Formations (Catalog number 1062).
- Named Lunar Formations included the satellite feature Plato A whose name was later changed to Bliss. It also included the designation Plato Z for an ill-defined valley to the north of Plato, terminating near Plato T. This valley is illustrated on Sheet SLC D1 of the later System of Lunar Craters, but the designation was not retained when lettered craters were added to the IAU Planetary Gazetteer in 2006.
- Amateur astronomers have adopted various schemes of naming the craterlets on the floor of Plato (none of which have official IAU designations). Some of these schemes somewhat confusingly re-use the IAU designations for lettered craters.
- The greenish Rand Mc.Nally moon map and the same moon map in Patrick Moore's Atlas of the Universe (1983) use the unofficial name Cape Plato for a feature at 57° North, 7° West (north of Plato, at Mare Frigoris).
- Howard Eskildsen has likened the system of craters Plato K and Plato KA (in Mare Imbrium, near Montes Alpes) to "a snowman with broomsticks for arms."
An Image of Suprises.
Impossibly High Standard.
A Hot Day on Plato
Plato in My Dreams
Half a Crater Shadowed
Peaks of Plato
Lacus Niger Major
Good night Moon
Pushing the Envelope (Smallest Detectable Lunar Crater).
A Classic View (shadow spires on Plato's floor, after local sunrise)..
Classic View (darkness on Plato's floor, before local sunrise).
Milk of Plato (an interesting observation by Phil Morgan, of possible Ashen Light on the floor of Plato).
L83: Crater pits at limits of detection.
- Ashbrook, J. 1959. A Plato Illusion. Sky and Telescope (December issue), p. 92.
- Marshall, K. P. and Mobberley, M. P. 1986. The Lunar Crater Plato. Journal of the British Astronomical Association. 96, 156-165.
- Wood, C.A. 200?. The Mysteries of Plato. S&T Online Article.
- Wood, C.A. Jul. 1999. The Mysteries of Plato. S&T July 199. v98 p122
- Google Scholar listing.
The lunar crater Plato in the Sourcebook Project (William R. Corliss)
- In Mysterious Universe, a handbook of astronomical anomalies (1979) :
- Page 203: Three Riddles of Plato (Jackson T. Carle, Sky and Telescope, 1955).
- Page 236: Unusual Lunar Phenomenon (A.V.Goddard, Popular Astronomy, 1932).