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SECRET SKY
Now that the best
apparition of Mars
in recent memory
has passed, I’d like to share
some thoughts on the illu-
sions of its canals. When it comes to canal sightings,
many observers mentally brush them away like cob-
webs. But to those interested in the history of astronomy
and how the eye/mind system works, the study of mar-
tian canals is like witnessing how a magician alters
visual processing with optical illusions.
As William Sheehan writes in the August
2015 issue of The Antiquarian Astronomer,
“The canals still exist — and will always
exist — in the subjective realm of illusion,
making their appearances when Mars is
viewed under the right conditions.”
In 2020, I dedicated much observing time
to seeking out martian canals — a difficult
task, as they were surprisingly rare and f leet-
ing. They don’t appear all over the planet at
once, as some maps of Mars suggest, but
singly and in f lashes so quick that the brain doesn’t
register them with a single sighting. As Percival Lowell
wrote in his 1906 book Mars and Its Canals: “For so
short and sudden are its apparitions that the locating of
it is dubiously hard. It is gone each time before he has
got its bearings. ... Such is the experience every observer
of them has had.”
In my studies, the features I would consider “canals”
materialized only when the planet appeared largest
(more than 20" in diameter). For the observations, I
used a 3-inch refractor at magnifications ranging from
300x to 400x — those typically used by Lowell, and
Giovanni Schiaparelli before him.Irradiation illusion
The Schiaparellian canal Indus was extremely promi-
nent this past apparition. In images, Indus appears as a
broad lane of irregularly dark terrain that includes Oxia
Palus. During moments of excellent seeing, I saw the
features clearly defined — but only when looking
directly at them. When my attention strayed, the sur-
rounding bright deserts created an irradiation illusion
that narrowed Indus into a thin, beaded linear canal.
The same illusion transformed a dimmer lane of dark
terrain in Chryse into the Schiaparellian canal
Hydaspes. These canals correspond to real albedo fea-
tures. As Eugene Antoniadi wrote in his 1930 book The
Planet Mars, “Schiaparelli’s ‘canals’ have a basis in real-
it y, though they do not exist on Mars as true cana ls.”Future seeing
According to neurobiologist Mark Changizi, author of
The Vision Revolution, “We see illusions because our
brains are attempting to see the future.” And motion,
he says, is crucial to the story of illusions. When the
brain attempts to generate a perception, Changizi says,
it does so by trying to fast-forward a tenth of a second.
As a result of this neural delay, we might not perceive
an image as it is, but as we expect it might soon be.
And so it appeared on a night of exceptional seeing
when I glimpsed the Schiaparellian canals
Chrysarrhoas and Sirenius. Unlike with
Indus, I could not associate their positions
with a linear albedo feature, ruling out the
irradiation effect. Both canals began at the
tips of pointed mare features. The tips served
as arrows that prompted the eye to extend
them in the direction they were pointing.
The canals always appeared in the mind’s
eye to drop down (to the north) from these
tips, like dripping paint.
In these latter cases, most likely, my brain
was gathering data quickly but not accurately. This left an
i mpre s sion of what my m i nd t hou g ht I shou ld see , r at her
t ha n what wa s re a l ly t here. A s L owel l h i msel f s a id i n Mars
and Its Canals, “Of a sudden be made aware of a vision as
of a thread stretched somewhere from the blue-green
across the orange areas of the disk. Gone as quickly as it
came, he will instinctively doubt his own eyesight, and
credit to illusion what can so unaccountably disappear.”
I’m interested in reading about other experiences.
Send your observations to [email protected].Seeing canals may not be so crazy after all.
Mind-altering Mars
ABOVE: In 1877, Italian
astronomer Giovanni
Schiaparelli first
described the
network of dark lines
on Mars we now call
canals. Amateur
astronomers can still
see and image them
today, as shown in
this shot (lower right)
by Sal LaRiccia
of Somerville,
Massachusetts, taken
October 14, 2020.
MAP: WIKIMEDIA COMMONS;
IMAGE: SAL LARICCIAUPPER RIGHT:
Schiaparelli added
notes to one of his
Mars maps (left). A
sketch by the author
(right) shows the
same region of Mars
on October 22, 2020.
MAP: WIKIMEDIA COMMONS;
SKETCH: STEPHEN JAMES O’MEARADuring
moments of
excellent
seeing, I saw
the features
clearly
defined.
BY STEPHEN
JAMES O’MEARA
Stephen is a globe-
trotting observer who
is always looking
for the next great
celestial event.BROWSE THE “SECRET SKY” ARCHIVE AT
http://www.Astronomy.com/OMeara