8/12/2019 The Mysteries of Plato

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The Mysteries of Platoby Charles A. Wood

Sunrise on the floor of Plato was captured in this video image made with a 6-inch Maksutov-Newtonian reflector on March 25, 1!Note the spirelike shadows cast "# the peaks on the crater$s eastern wall! %n a matter of several hours, these shadows shrink to a

fraction of the length seen here!Courtesy Dennis di Cicco.

The crater Plato is one of the superstars for observers of the Moon. It is big (101kilometers wide) conspicuous with its dark floor ringed b! a bright rim andlong a sub"ect of detailed scrutin! speculation and controvers!.

The view through a telescope is especiall! intriguing because of the irregularit!of Plato#s rim as shown dramaticall! b! variations in lengths of shadows castonto its floor. $ccording to old measurements reported in Thomas %w!n&lger#s 1' book The Moon, three peaks on the eastern rim rise 1. 1.' and*.1 kilometers above the floor. +n the western rim an obvious large triangular

massif is partiall! disconnected from the crater rim. This 1,km,long block andanother one farther north resulted from giant landslides where segments of therim slid slightl! inward creating a scallop - a bite out of the circular rim.ariations in rim height and width ma! thus be due to slumping but the heightdifferences on Plato#s east rim must be of older unknown origins.

+ne Plato m!ster! with a simple solution is its lack of a central peak. /ompared

to other craters of similar sie Plato should have a *.*,km,high mountain risingfrom its floor. owever since Plato is filled with a *.2,km la!er of lava the peak is buried.

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&ow man# craterlets can #ou see on Plato$s floor' (lthough some o"servers have reported do)ens, onl# four craters are sufficientl#o"vious to "e seen with moderate telescopes even when o"serving conditions are stead# and the illumination angle is favora"le!*he largest of the four measures 2!2 kilometers across!Courtesy Brown/NASA Northeast Regional Planetary Data Center.

3or more than 100 !ears the floor of Plato has been the focus of intense 4uasi,scientific debate over suspected lunar changes. Three t!pes of observations

caused controvers!5 detection of small craters on Plato#s floor variation in floordarkness with changing 6un angles and obscurations of the floor itself. 7ecausethe floor possesses a few small impact craters near the limit of visibilit! withsmall telescopes there have been unofficial contests to detect the largestnumber of craters. arvard astronom! professor 8.. Pickering apparentl!won in 1'* b! announcing his mapping of 91 spots on Plato#s floor.

/omparison of hand,drawn maps with high,resolution photographs obtained b!the :unar +rbiter ; spacecraft in 129 demonstrates that the observers diddetect the four largest craters and some of the smaller ones but their estimatesof sies locations and numbers were often seriousl! in error.

/raterlets were not the onl! source of controversial observations. $ccording to

&lger <The gradual darkening of the floor of Plato as the sun#s altitudeincreases from *0= till after full moon ma! be regarded as an established factthough no feasible h!pothesis has been advanced to account for it.< $ctuall!

 "ust the opposite is true according to measurements of the floor#s brightness b!sensitive photometers mounted on large telescopes. :ike the rest of the Moon

Plato#s floor brightens until near full when it rapidl! gets much brighter andthen darkens after full Moon.

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Plato area highlighted!Courtesy Dennis di Cicco.

The third of Plato#s controversies concerns reports that the dark floor isoccasionall! obscured b! mists or clouds. Most of the observations were madeduring the last centur!> 8alter %oodacre#s 1?1 book also called The

 Moon,mentions that there are <a number of well authenticated cases.<

@escriptions include a fog that cleared as the 6un rose a <curious luminousmilk! kind of light< and a nondescript lack of detail. $nother 1th,centur!observer found that the floor was covered b! m!riad points of light <as ifreflected from flocculent clouds l!ing near the surface.<

In contrast with these visual observations in none of the man! photographstaken b! space probes or b! large telescopes have there been obscurations of

Plato#s floor. Perhaps like A3+#s onl! believers see them.