Sky & Telescope - June 2020 - 6

FROM OUR READERS
to perceive the Martian craters normally but instead saw reversed relief.
To correct this, I removed the slides
from the tray, ﬂ ipped them 180° (front
to back), and replaced them in the
tray. This corrected the inverted depth
perspective for those individuals.
Alas, about 10% of the audience
that previously were able to correctly
perceive the Martian craters now saw a
reversed relief image instead!

Young Astronomy
I want to thank you and the AAS for
making S&T the premiere magazine for
astronomy. I'd also like to introduce perhaps your youngest reader, Calvin, our
grandson, who is 3 months old. It's never
too early to get started in astronomy.
Paul L. Livio
Torrance, California
u Three-month-old Calvin has a gander at our
January 2020 issue.

Thanks for the engaging article "The
Martian Underground" (S&T: Jan. 2020,
p. 34). It's likely that any life on Mars
today can only survive deep underground and, as with subterranean organisms here, must be exceedingly diverse in
respect to energy sources and metabolic
adaptations. The most tantalizing question is whether it's DNA-, RNA-, and
protein-based, like terrestrial life, or if
it has an alternate biochemistry. If it is
similar, that raises questions as to where
it originated, and if it could be the result
of past cross-contamination between
the two planets. Conversely, if putative
Martians exhibit signiﬁcantly different
biochemistries, it would imply that they
originated independently. Either way, the
answers would have profound implications as to how and where life originated
and how common it is in the universe.

Until Ed's letter, I thought I was the
only one with this issue. Now, I also
wonder how many others may have
struggled with this problem. However,
despite the hillocks, I enjoy observing the
wonderful beauty of God's astronomical
creation and, occasionally, I see craters!
Scott Alford
St. James, Missouri

Klaus Brasch
Flagstaff, Arizona

I read Ed Wagner's letter with interest.
This reversal often happens to me, particularly when looking at an image for
the ﬁrst time. I haven't experienced the
reversal through the eyepiece, though.
Sometimes, I rotate the page or look at
the image with light coming from a different direction. It doesn't always work!
Other times, I can make the reversal
happen just through concentration,
ﬂ ipping between domes and craters.
It's an interesting phenomenon and
sometimes exasperating. I know of one
other person who has noticed it, too.

Lunar Inversion

James Edgar
Melville, Saskatchewan

I have been enjoying S&T since the late
1970s and never felt the need to write in
until reading the letter from Ed Wagner
(S&T: Feb. 2020, p. 6).
Ed, you're not alone! For about the
past 30 years, 99% of all Moon images
I have seen in pictures or videos appear
"reversed." Try as I might, I cannot get
the little hillocks to turn into craters,
even though I know they are craters and
should be depressed. Forty years ago, I
did not have this problem. While watching the Apollo 11 lunar-landing videos as
a youngster, I saw craters as craters.

I frequently notice this "reversed topographical relief" when viewing photos
of lunar and Martian craters. When
this occurs, I rotate the photograph
180°, look away, and then look back.
This inevitably resets my brain to the
proper topographical relief perspective.
Many years ago, I gave a presentation, using a slide projector, of images
of Martian landforms that were
recently received from a spacecraft
orbiting Mars. I was surprised when
about 10% of the audience was unable

JUNE 2 02 0 * SK Y & TELESCOPE

As a geologist who has worked with
Landsat and other types of aerial imagery throughout my career, what Ed experienced is a common phenomenon.
When working with hard copy
images, a cure for this "reversal" is to
physically turn the image upside down
and view it from the opposite direction.
This ﬁxes the image for me most of the
time. When it doesn't work or if I am
viewing digital images and can't physically turn them, then I force myself to
think about the direction of the light.
It's not easy to "ﬂip the image" once
your brain has locked onto a particular
view, and I commend Ed for having success most of the time. As a last resort,
take a break and come back to the image
or scope after some time. The brain may
self-correct after the break.
Thomas Jones
Spring, Texas

The optical phenomenon described by Ed
Wagner is called pseudocopic vision. It
is described in Richard L. Gregory's book
Eye and Brain.
There is also an optical instrument
known as a pseudoscope that reverses
depth perception. I have seen this
phenomenon a few times with a 5-inch
Maksutov-Newtonian.
Spurious resolution, however, though
not as common, is responsible for some
of the reports of the "canals" seen on
Mars. Spurious resolution is usually
seen in out-of-focus photographs.
Human eyes and brains can be easily
fooled (as any magician will tell you).
Rodger Gordon
Nazareth, Pennsylvania

CA LVIN A ND PAUL LIVIO

Micro Martians

Frank Ridolfo
Bloomﬁeld, Connecticut

Sky & Telescope - June 2020

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