From: LARRY KLAES (ljk4@msn.com)
Date: Wed Sep 18 2002 - 06:53:06 PDT
What Lowell Really Saw When He Watched Venus
September 10, 2002
By LEON JAROFF
While an observatory in Arizona bears his name, Percival
Lowell is best known for his obsession with Mars and his
conviction that intelligent life had once existed on the
planet.
That notion was not finally put to rest until 1972, when
close-up pictures from the Mariner 9 spacecraft, in orbit
around Mars, revealed a desolate landscape with no evidence
of any artificial structures.
Now, after more than a century, another Lowell observation
that has been even more controversial - the wheel-like
"spokes" radiating from a "hub" on Venus - has finally been
explained.
With his 24-inch telescope in the Lowell Observatory, which
he founded near Flagstaff, Ariz., in 1894, Lowell spent 15
years viewing Mars and sketching what he perceived as a
network of fine lines connecting the polar cap with a
number of dark areas.
In lectures, and as author of three popular books about
Mars, he argued that the lines were canals built by an
intelligent civilization to bring water from the melting
polar cap to oases on an arid and dying planet.
Other astronomers before him, like Giovanni Schiaparelli of
Italy, had also observed what they perceived as canals or
other configurations on Mars.
Yet no one but Lowell had ever seen anything on Venus
resembling spokes, or any other linear markings, for that
matter.
Though the planet seemed permanently enshrouded in a thick,
featureless cloud cover, Lowell believed that the markings
could have been surface features visible through a dense
but translucent atmosphere.
Even more puzzling, he insisted that because the spokes
were always facing the Earth, Venus must be in synchronous
rotation with the Sun, a highly unlikely relationship.
Under a barrage of criticism and even some derision, Lowell
in 1902 briefly recanted, publishing a retraction of his
Venus work.
But when the spokes showed up again in his 1903
observations, he adamantly insisted on their reality until
his death in 1916.
Intrigued by the enigma of the spokes, which is scantily
treated in most stories about Lowell, Dr. Bill Sheehan and
Tom Dobbins, amateur astronomers and contributing editors
of Sky & Telescope, published a detailed article called
"Lowell and the Spokes of Venus" in its July issue.
Their article included a little-known fact: to reduce the
glare from Venus, the brightest object other than the Moon
in the night sky, and to steady the image, Lowell had
narrowed the aperture of his 24-inch telescope to only 3
inches or even less.
With this information, the authors had unwittingly provided
the key to the puzzle of the spokes.
Upon reading the article, several optometrists and
ophthalmologists immediately grasped the significance of
that revelation.
Lowell's large refracting telescope, set at 144X
magnification and with an aperture narrowed down that far,
they figured, had a focal ratio of at least f/120.
In simple terms, this meant that the setup was the
equivalent of placing a card with a pinhole in front of
Lowell's eye and shining a bright light through it.
The discerning readers concluded that the telescope was
actually mimicking an ophthalmoscope, an instrument used to
examine the interior of the eye.
What Lowell saw as spokes were actually shadows of the
blood vessels and other structures in his own retina.
In the letters column of the current issue of Sky &
Telescope, Dr. Sheehan and Mr. Dobbins share this insight
and drive home their point with two striking circular
images, one a Lowell sketch of the Venusian spokes, the
other a photograph of retinal blood vessels.
The two patterns are uncannily alike.
"It isn't often,"
the authors note, "that one writes an article for a monthly
publication about a 100-year-old mystery and sees it solved
before the next issue is in print."
http://www.nytimes.com/2002/09/10/science/space/10VENU.html?ex=1033356888&ei=1&en=78c8a7596528f735
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