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| A Very Short History of the
Telescope |
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Galileo
and his Refractive Telescope |
Newtons
Reflective Telescope
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| For thousands of years men and
women sought to discover the mysteries of the night sky, but the quantum
leap from naked-eye observation to instrument added vision was one of
the great technological advances of mankind. It began with the lens. It's origin is
unknown, but spectacles were being worn in Italy as early as 1300.
The inventor was probably making glass disks for leaded windows; he
probably tested the clarity of a disk by looking through it and
discovered that he could see better.
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Lippershey
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| The telescope was the first optical
instrument and its origin is surrounded by controversy. The
most likely story puts it in the shop of an obscure Dutch spectacle
maker named Hans Lippershey, about 1600. Two children were playing
with his lens, put two together, peered through them at a distant church
tower and saw it wonderfully magnified. Lippershey looked for
himself and soon mounted lenses together, creating his
"looker." In 1608, Lippershey tried to sell it to
the Dutch army, but his offer was eventually turned down because of
claims from others that they had invented it. New of the invention
spread rapidly. That same year the French ambassador at the Hague
obtained one for King Henry IV, and in the next year, they were being
sold in Paris and Germany under the name of "Dutch Trunks,"
"perspectives" and "cylinders." They soon
appeared in Milan, and Venice and by end of the year, they were being
made in London.
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Galileo
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The most influential person connected with the telescope in
its early days was the Italian scientist Galileo. Within a month
of Lippershey trying to sell his looker to the Dutch Army, word of the
invention reached Venice when an unidentified stranger tried to sell one
to the Senate, who referred the matter to its scientific adviser Paolo
Sarpi, who examined it. But then the stranger and his instrument
disappeared, so Sarpi went to see Galileo, the city's most respected
instrument maker, who had just invented a new calculating device and
described it. Galileo then "reinvented" it. The
instrument was met with criticism and controversy as many felt that it
did nothing other than create optical illusions and the image could not
be trusted. In March of 1610, he published a description of
his night sky observations as The Starry Messenger (Sidereus
Nuncius),. Although it contained only twenty four pages, it
astonished and troubled the learned world. He reported that the moon was
not smooth, as previously believed, but rather rough and covered with
craters; that the Milky Way was composed of millions of stars and
Jupiter had four moons. The latter led him to challenge the
long accepted geocentric view of the world system (the universe revolves
around the Earth) and accept the heliocentric (the solar system revolves
around the Sun) proposed some fifty years earlier by Copernicus. Galileo
had proof!
On the night of April 14, 1611, a banquet was held in
his honor outside Rome. Galileo showed the guests his instrument
and let them see his discovered. An unidentified Greek
poet-theologian happened to be present and he proposed a name for the
instrument, one borrowed from ancient Greece. It was quickly
accepted and the host, Federico Cesi, then officially christened
Galileo's instrument, "the telescope."
These first optical instruments were what the average person identifies with the
word "telescope," a long thin tube where light passes in a
straight line from aperture (the front objective lens) to the eyepiece
at the opposite end of the tube. These have come to be
called refractive telescopes, because the objective lens bends, or
refracts, light. They were used by all the
great early astronomers - Galileo, Kepler, Huygens, and Hevelius.
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Newton
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| Some seventy years later, Isaac
Newton, inspired by Kepler’s work on optics and Robert Boyle’s
recent experiments with color, explored the way a prism refracts white
light into a array of colors. He recognized that a lens was a circular
prism and concluded that the separation of colors, known as chromatic
aberration (see below) limited the effectiveness of existing telescopes. He created
a new telescope design, one that used a parabolic mirror to collect
light and concentrate the image before it was presented to the eyepiece.
This resulted in the Reflective Telescope.
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