Sky & Telescope - USA (2020-06)

CALVIN AND PAUL LIVIO

FROM OUR READERS

Micro Martians

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 under-

ground and, as with subterranean organ-

isms here, must be exceedingly diverse in

respect to energy sources and metabolic

adaptations. The most tantalizing ques-

tion 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 signifi cantly different

biochemistries, it would imply that they

originated independently. Either way, the

answers would have profound implica-

tions as to how and where life originated

and how common it is in the universe.

Klaus Brasch

Flagstaff, Arizona

Lunar Inversion

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 watch-

ing the Apollo 11 lunar-landing videos as

a youngster, I saw craters as craters.

I want to thank you and the AAS for

making S&T the premiere magazine for

astronomy. I’d also like to introduce per-

haps 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

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

I read Ed Wagner’s letter with interest.

This reversal often happens to me, par-

ticularly when looking at an image for

the fi rst 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 dif-

ferent 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.

James Edgar

Melville, Saskatchewan

I frequently notice this “reversed topo-

graphical 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 presenta-

tion, 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

to perceive the Martian craters nor-

mally 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!

Frank Ridolfo

Bloomfi eld, Connecticut

As a geologist who has worked with

Landsat and other types of aerial imag-

ery throughout my career, what Ed expe-

rienced 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 fi xes the image for me most of the

time. When it doesn’t work or if I am

viewing digital images and can’t physi-

cally turn them, then I force myself to

think about the direction of the light.

It’s not easy to “fl ip the image” once

your brain has locked onto a particular

view, and I commend Ed for having suc-

cess 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

Young Astronomy

uThree-month-old Calvin has a gander at our

January 2020 issue.

6 JUNE 2020 • SKY & TELESCOPE