Relive the Discoveries of Galileo September 2014 | Page 4

Relive the Discoveries of Galileo

In 1608, Hans Lippershey, a German-Dutch lens
maker, applied for a patent on his design of a
“perspective glass”, a weak telescope or spy-glass
that could magnify three times. Word of Lippershey’s

Galileo with some of his pupils in Piazza San Marco, Venice, as he
tests the first lenses with which he will construct his telescope, Luigi
Catani, 1816, Florence, Palazzo Pitti, Gallery of Modern Art.

design spread throughout Europe, reaching the
inquisitive Galileo in the summer of 1609, as he
taught at the University of Padua. Anticipating its
military and commercial value instead of its potential
for studying the heavens, Galileo immediately built
his own telescope to impress the Venetian senators,
viewing from the towers in Venice. They were so
amazed with the ability of the spyglass to discern the
nationality of vessels on the horizon, hours before the
best-sighted lookouts could, that they offered Galileo
tenure at the university and a better than five-fold
raise in pay.
Later that November, in a whim
of curiosity, Galileo decided to
turn an improved version of his
telescope at the Moon. What he
saw – jagged mountains, valleys
and craters – came as a
shocking surprise.
He was
encouraged to build ever
stronger telescopes for closer
examination. By the end of
1609, Galileo had sketched the
moon at different phases, and
declared it to be just like Earth
Galileo’s drawings of the
Moon’s rugged surface
with its mountains and valleys,
hardly the perfect sphere Aristotle claimed all
heavenly bodies to be.
One month later, in January 1610, Galileo aimed his
-4-

telescope at Jupiter and made one of his most
significant discoveries: four moons in orbit around
the planet, knocking down another tenet of Aristotle
and Ptolemy that all heavenly bodies orbit the Earth.
Not all do, he discovered. If there could be moons
orbiting Jupiter, then maybe the Earth could be in
orbit too, perhaps around the Sun as the Polish
philosopher Copernicus advanced in his book De
revolutionibus, published 67 years earlier!
In addition, Galileo’s scope showed that all the
planets were evenly-lit bounded circular shapes,
unlike the fixed stars that blaze and scintillate without
shape. By using a telescope to scan the Milky Way,
he found it to be the home of an immeasurable
number of tiny stars.
Galileo announced his
discoveries in Sidereus Nuncius (The Starry
Messenger), an instant
sensation. All 550 copies
printed in March 1610 were
sold within hours and were
soon in the hands of
monarchs, royal astronomers
and philosophers throughout
Europe. Galileo’s fame
spread with his book, and so
did an undercurrent of
resentment by a number of
priests and professors whose
lifetime of teachings and
authority he threatened. They
disliked the direction Galileo’s work was heading.
In the following months and years, Galileo
discovered the rings of Saturn (actually, his small
telescope could not resolve the rings clearly and he
thought Saturn to be a triple planet), that Venus
passes through all phases like the moon, and, most
baffling of all, that the Sun appeared to have
imperfections on its surface. “…in the very face of
the sun,” Galileo described, “these innumerable
multitudes of dense, obscure, and foggy materials are
discovered to be produced and dissolved continually
in brief periods.” He had found sunspots!
Long before his discoveries with the telescope,
Galileo knew of Copernicus’s sun-centred theory, and
found it compelling that the earth would move around
the sun. With the observational evidence he gathered
through his telescopes, he was convinced Copernicus

For more information about DRAA publications, please visit our website: www.drastronomy.com