MMM Classics Year 10: MMM #s 91-100 - Moon Society

Starting your backyard/armchair tour:
Mare Crisium, the Sea of Crises
by Thomas Heidel, LRS - an MMM-Pleiades exclusive
Asked to do a series on backyard telescope observing
of the Moon, the first decision I made was to bring along all of
you who do not (yet) have (access to) a telescope or even a pair
of binoculars. All armchair amateurs will need for our
“Settlers’ Viewpoint Tour” is a decent map of the Moon’s near
side, and/or a photographic atlas of the Moon.
Next I decided to start with the easiest feature on the
Moon to pick out with the naked eye, a circular mare or gray
lava plain that stands alone from the “chain” of interflowing
maria that dominates nearside, and which is easily picked out
by the naked eye from first crescent (morning shadows) up to
four days after full Moon (evening shadows at Crisium). More
billions of people have noticed Crisium (without knowing its
name) than any other feature. At 10-17˚ N, 50-70˚ E, it is the
right eye of the “man in the moon”. Imagine the Moon’s E-W
path through the night sky. Tilt your head perpendicular to it,
and Crisium is in the upper right quadrant. Through an imageinverting
telescope (not binoculars), find it to the lower left.
Crisium at (a) local morning, (b) local noon, (c) local evening
(a) ‘96: 3/22, 4/20, 5/20, 6/19, 7/18, 8/17, 9/15, 10/15, 11/14
(b) ‘96: 3/28, 4/26, 5/26, 6/25. 7/24. 8/24. 9/21, l0/21, 11/20 (c)
‘96: 4/6, 5/5, 6/3, 7/2, 8/1, 8/30, 9/28, 10/28, 11/27.
Along with other major nearside seas, it’s name first
appears in Riccoli’s 1651 chart of the Moon. 260 miles N-S
and 370 E-W, its 66,000 sq. mi. compares to Wisconsin plus
Michigan’s Upper Peninsula. It has some easy-to-see features.
Out on the mare the crater [1]Picard (Jean, not Jean-
Luc) with a small central hill is easy to find. To the north of it
find smaller [2]Pierce. Look from Picard towards the near
western shore and pick out the incomplete rim of the larger but
lava-sheet flooded crater [3]Yerkes. Kokh [1] has suggested a
new nomenclature for crater rim remnants poking through the
mare fill: saxa (Latin for reefs). Between Saxa Yerkes and the
mare coast look for a long flat gray area. In [1] “Expanding
Lunar Nomenclature”, in Selenology: (American Lunar Soc.
quarterly, issue # unavailable at press time) Peter Kokh has
suggested another feature category be adopted: fretum (Latin:
straight). Keeping within the meaning orbit of “crisis”, he
suggests [4]Fretum Hodiernum (Straight of Today) for this
area. Past it a ways into the bordering highlands ([5]Ora
Vigilium, Coast of Sentries) is one of the brightest lunar craters,
[6]Proclus, often changing its appearance to careful observers,
suggestive of “transient lunar phenomena”. Beacon bright, it is
a very easy feature to pick out. Beyond Proclus, on the fringe
of Mare Tranquilitatis, lies [7]Palus Somni, Marsh of Sleep.
Moving counterclockwise past [8]Lick, and again a
short distance into the border highlands along the south, find
the crater [9]Auzouit, and south of it the larger dark floored
crater [10]Firmicus, and past it, a small irregular dark plain
called [11]Mare Undarum, the Sea of Waves. Now look for
cape [12]Agrarum on Crisium’s SE coast. Beyond it lies an
unnamed bay (Kokh: [13]Sinus Constantiae, Bay of
Constancy). To the ESE find the large flat-floored crater
[14]Condorcet. East of Crisium lie [15]Hansen and
[16]Alhazen, and beyond another irregular unnamed marefilled
area (Kokh: [17] Lacus Spei, Lake of Hope).
Just past Crisium’s NE coast, beyond the crater
[18]Eimmart, find another irregular mare-flooded valley
known as [19]Mare Anguis, Serpent Sea. From its shores,
Earth is a comfortable picture postcard distance above the
WSW horizon. Redubbing the valley “Angus Bay”, Gregory
Bennett, chief architect of the Artemis Project suggests this
site for a first commercial Moonbase. Precisely because
Crisium is so easy to pick out with the naked eye, from a
publicity/public awareness point of view alone, Crisium seems
prime turf for a first outpost. Its coasts and shores offer access
to Al-rich highland and Fe/Ti-rich mare soils alike. Kokh’s
favored site is Fretum Hodiernum, across the mare, handier to
the rest of nearside.
Directly north of Crisium is the dark flat-floored
crater [20]Cleomedes, very easy to pick out in binoculars, and
the crater [21]Delmotte to the east, back towards Mare Anguis.
To the WNW of Crisium find [22]Tisserand, and just
beyond it the larger [23]Macrobius. Between Tisserand and
Crisium, and north of Macrobius are a two irregular unnamed
mare-flooded valleys. (Kokh: [24]Lacus Parationis, Lake of
Readiness; and [25]Lacus Vigilantiae, Lake of Vigilance.)
Back to Crisium itself. Notice the subtle differences in
shading out on the mare floor, indicating the exposed areas of
distinct episodes of lava-sheet flooding, each with slight
(advantageous?) differences in regolith-soil composition.
Revisit Crisium frequently at different phases and
local lighting conditions. Learn to recognize the features
mentioned above. Appreciate the differences between
individual features. Make yourself at home! TH
Moon Miners’ Manifesto Classics - Year 10 - Republished January 2006 - Page 33