Sky & Telescope - October 2019 - 52

OCTOBER 2019 OBSERVING
Exploring the Moon by Charles Wood

Lunar
Pareidolia
Our vivid imagination can
make us see more than
craters on the Moon.

OCTOBE R 2 019 * SK Y & TELESCOPE

p Patterns formed by the large lunar maria visible during full Moon suggest a man's face, a
woman's profile, or even a leaping rabbit. How many can you see?

sent Promontorium Heraclides on
the west side of Sinus Iridum as the
proﬁle of a woman with hair streaming
westward along the boundary between
Mare Imbrium and Montes Jura. Fastforward to the 1820s, when German
observer Franz von Paula Gruithuisen
reported seeing an area north of the
crater Schröter that displayed nearly
straight walls, with others branching off
at 45° angles. Immersed in the romantic
belief that life was nearly everywhere, he
concluded that these features were a city
as seen from above, naming it Wallwerk.
These examples distinguish between
interpretations of observed features
as real phenomena and recognition of
just a similarity of shape. While Cassini
didn't really think that Promontorium
Heraclides was in fact the head of a giant
woman, Hevelius did truly believe that
Copernicus was a volcano. Likewise,

Gruithuisen mistakenly thought his
Wallwerk was indeed an artiﬁcial construction. Interpretations can be proved
right or wrong with better information,
but examples of pareidolia are imaginative comparisons that make observations
more descriptively interesting.
Surprisingly, only a few lunar features
have pareidolic nicknames. Perhaps the
best known is the Lunar X, a conspicuous cross that appears on the terminator when the Moon is near ﬁrst quarter
phase. It's a ﬂeeting apparition created
by adjacent crater rims that catch the
rising sunlight for only a few hours
before the surrounding area is illuminated, causing the cross to vanish. The
northeastern and southeastern walls of
the 115-km-wide crater Purbach make
the western half of the X, and the western rims of La Caille and Blanchinus
comprise the eastern half.

EDDIE TRIM A RCHI
CREDIT

ur minds tend to seek out familiar
patterns everywhere, trying to
wrest order from ambiguity. According to the Merriam-Webster Dictionary,
the tendency to perceive a speciﬁc,
often meaningful image in a random
or ambiguous visual pattern is known
as pareidolia. Astronomers are familiar
with many examples of pareidolia, such
as seeing the shape of a continent in
a nebula (see page 54), or a woman's
proﬁle in the maria visible at full Moon.
Most constellations are themselves
simply the standardized acceptance of
ancient Greek pareidolic characterizations of star patterns as humans,
animals, and even musical instruments.
Recognizing such patterns helps us to
navigate the night sky, aiding in how we
communicate the locations of speciﬁc
areas and events to one another.
Calling the dark maria as seen at full
Moon a man, woman, or even a rabbit
was common across many societies for
thousands of years. Ancient Greek and
later Arabic astronomers believed that
the Moon was a smooth, mirror-like
sphere and the maria to be reﬂections
of Earth's oceans. The invention of
the telescope did little to dispel these
myths: On his 1647 map of the Moon,
Johannes Hevelius compared the crater
Copernicus to Earth's Mount Etna, a
nearly circular volcano rising above the
surrounding Mediterranean Sea.
Almost a quarter century later,
improved telescope optics allowed
Giovanni Domenico Cassini to repre-

Sky & Telescope - October 2019

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