http://www.skyandtelescope.com.au 59- Mare Crisium In the days right after new Moon, you’ll
spot the sizable grey oval about 580 by 430 kilometres across
that marks Mare Crisium, the ‘Sea of Crises,’ near the
centre of the graceful lunar crescent. Before the telescope’s
invention, moonwatchers really did believe that this and
other dark patches were briny seas; today we know they are
vast plains of dark, solidified lava that flooded the floors of
impact basins billions of years ago. - Proclus Just beyond the western lip of Mare Crisium
isProclus,asmallishcrater(27kilometresacross)witha
substantial fan of bright-toned debris that splashed out onto
thesurroundinglandscape.Thispatternofrayshasadistinct
gapthatshowsupparticularlywellattimesnearfullMoon.
ApparentlyProclusresultedfromtheimpactofawayward
objectcominginfromthewestataveryshallowangle,and
thissidewaysstrikecreateda‘zoneofavoidance’wherethe
brightfanisabsent.
3.PosidoniusNotmuchremainsofthis95-km-wide
crater—lavafromMareSerenitatisfloodeditsinteriorand
allarounditbillionsofyearsago.Whenthelocalshadows
arepronounced,lookonthecraterfloorforanetworkof
fractures (rilles)causedbysurfaceextensionand‘wrinkle
ridges’ (dorsa)oflavacausedbycompression.
4.Serpentine Ridge This snaking, 480-km-long chain of
wrinkleridgesrunsparalleltotheeasternedgeofMare
Serenitatis.Theverticalreliefislow,nomorethan300
metres,butthetwistinghillsshowupdistinctlyifyouview
thisregionwhentheMoonis6daysold.
5.TheophilusAlong the northeastern margin of Mare
Nectarisstandsatrioofcratersallabout95kmacross.
Theophilus(atthetrio’sbottom)looksfreshestandcutsinto
therimofCyrillustoitsimmediatesouthwest—soit’sthe
youngest.Catharina,totheirsouth,hasbeenbadlybattered
and is the oldest.
6.Fracastorius The northern rim of this 124-km-wide crater
ismissing.ItliesonthesouthernmarginofMareNectaris,
andchancesarethatthecentreofNectarisdroppeddown
afterFracastoriusformed.Greatfloodsofmarelavathen
inundatedthelow-lyingnorthernrim.Thatdowndroplikely
alsoexplainsthedelicaterillesthatweseecrisscrossingthe
crater’s floor.
7.Rupes AltaiThislong,prominentgashinthelunar
crustisactuallyallthat'sleftofthemainringofNectaris
basin, which was an enormous pit created some 3.92 billion
yearsago.Therestoftherimhasbeenerasedbysubsequent
impacts and lava flows. Informally known asAltai Scarp,this
formation stretches roughly 480 kilometres and stands more
than1.5kmhighinplaces.It’smostevidentwhenlitbythe
risingSun(about6daysafternewMoon)ornearlocalsunset
abouttwoweekslater.
8.Plato Probablythemostdistinctflat-flooredcrateron
theMoon,Platoisbig(100kmacross)withasmooth,flat
andnearlyfeaturelessfloor.There’snocentralpeak,because
Plato’slavapoolismorethan2.5kmdeep.Thecrater’s
irregular rim casts menacingly pointed shadows across the
floorastheSunrisesoverthem;thebesttimetolookatPlato
crater is about 9 days past new Moon.S MORNING LIGHT A low Sun lights up Altai Scarp (arrowed), which
marks the outer ring of 8,605-km-wide Nectaris basin. Mare Nectaris
(near the top) is the lava plain that later filled its centre.S IG SPLASH B Check out dark Mare Crisium and the small-yet-
obvious crater Proclus, whose splash of bright rays (seen most easily at
times near full Moon) shows an obvious gap to one side.RICARDO BORBAGARY SERONIK