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The human eye in space by Lambert Parker (edited)
Human visual hardware is a result of a billion years of evolution within
the earths atmosphere where light is scattered by molecules of air,
moisture, particular matter etc. However as we ascend into our atmosphere
with decrease density, light distribution is changed resulting in our
visual hardware receiving visual data in different format.
Some Aspects to Consider:
1. Visual acuity is the degree to which the details and contours of
objects are perceived. Visual acuity is usually defined in terms of
minimum separable.Large variety of factors influence this complex
phenomenon which includes :
# Optical factors- state of the image forming mechanisms of
the eye.
# Retinal factors such as the state of the cones.
# Stimulus factors such as illumination, brightness of the
stimulus, contrast between the stimulus and background,
length of time exposed to the stimulus.
* Minimum separable: shortest distance by which two lines can be separated
and still be perceived as two lines.
"During the day, the earth has a predominantly bluish cast..... I could
detect individual houses and streets in the low humidity and cloudless
areas such as the Himalaya mountain area.... I saw a steam locomotive by
seeing the smoke first..... I also saw the wake of a boat on a large river
in the Burma-India area... and a bright orange light from the British oil
refinery to the south of the city (Perth,Australia.)"
The above observation was made by Gordon Cooper in Faith 7 [1963] and
which generated much skepticism in the light of the thesis by Muckler and
Narvan "Visual Surveillance and Reconnaissance from space vehicles" in
which they determined that a visual angle of ten minutes was the
operational minimum, and that the minimum resolvable object length
[M.R.O.L] at an altitude of 113 miles would be 1730 ft. This limitation of
acuity was revised the next year to 0.5 seconds of arc for an extended
contrasting line and 15 seconds of arc for minimum separation of two
points sharply contrasting with the background.
Orbiting at 237 miles in the skylab it was possible to see the entire east
coast [Canada to Florida Keys] and resolve details of a 500 feet long
bridge based on inference. Of Interest is the fact that even though the
mechanical eye [camera systems] can resolve objects greater than fifty
times better than the human eye, without the human ability to infer,
interpretation of the data is meaningless.
Conclusion: Visual acuity in space exceeds that of earth norm when objects
with linear extension such as roads, airfields, wake of ships etc.
Stereoscopic vision: the perception of two images as one by means of
fusing the impressions on both retinas. In space one has to deal with a
poverty of reference points. For hardware evolved in a reference oriented
paradigm, this possess a grave problem. Once out of the space craft and
gazing outward, the eye can only fix on the stars [without even a twinkle]
which for all practical purpose is at infinity ie. without stereoscopic
vision "Empty field myopia" prevails.
Empty Field Myopia is a condition in which the eyes, having nothing in the
visual field upon which to focus, focus automatically at about 9 feet. An
astronaut/cosmonaut experiencing empty field myopia focusing at 9 ft would
be unable see objects at a range close as 100 ft. If another spacecraft,
satellite, meteorite or L.E.M entered his field of vision, he would not be
able to determine the size nor the distance.
Solution:
Man does not face any hostile environment in his birthday suit, the
clothing industry and need for walk in closet say it all. In space we
will wear our exoskeleton just as we wear winter jackets in winter and we
will wear our helmets with visors to maintain our internal environment,
filter out all those nasty rads etc. Since Empty Field Myopia is secondary
to loss of reference points why not just build them into the visor itself
giving the eye points of reference-- create a virtual reality ??? This
line of speculation leads to amazing concepts......
PERCEPTION OF COLORS.
Studies done by the Russian cosmonauts on effects on perception of colors
in space suggests a reduction in the perception of brightness of all
colors. The greatest degradation seem to affect purple, azure, & green.
LIGHT FLASHES.
Not the so-called fireflies noted in orbital flights by astronauts [shown
graphically in the movie right stuff] but lights as faint spots / flashes
seen after dark adaptation in the cabin of the Apollo missions. Generally
described as white/colorless and classified as three types.
# Described as "spots" / "starlike" 66 % of the time. Appearing in both
eyes simultaneously or one eye at a time.
# Described as "streaks" 25 % of the time.
# Described as "lightning discharge seen behind clouds" 9 % of the times.
It was of interest that the very same astronauts who reported them in the
Apollo flights failed to see them in previous Gemini flights. After the
Apollo flights this phenomena was noted by the crew of all three Skylab
missions especially when they crossed the South Atlantic Anomaly.
W.Zachary Osborne, Ph.D., Lawrence Pinsky, Ph.D., at University of Houston
& J.Vernon Bailey at Lyndon B. Johnson Space Center conducted an
investigation on this phenomena and concluded that they were due to heavy
cosmic radiation penetrating thru the craft and impinging on the retina to
cause this phenomena of flashes. The fact that this was noted only after
the eyes were darkadapted points to retinal interaction than optic nerve
per se.
ADDITIONAL FEATURED ESSAYS
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