International Year of Astronomy - Galileo's Discoveries
Galileo Galilei (1564 - 1642)
In the 17th century, Italian astronomer, physicist, and
philosopher Galileo Galilei was the first person to use a new optical
instrument that he called a perspicillum-known
today as a telescope-to look at the sky.
Galileo's first telescope was made from available lenses and
gave a magnification of about four times. To improve on this, Galileo learned
how to grind and polish his own lenses and by 1609 he had an instrument with a
magnification of around eight or nine times. The astronomical discoveries he
made with his telescopes were described in a short book called the Sidereus Nuncius ("Sidereal Messenger"),
published in Venice in 1610.
Galileo discovered several points of light close to the
planet Jupiter and assumed that they were stars fixed in the heavens, but their
strange alignment intrigued him. When he looked again the next night, Galileo
saw that they had changed position. Galileo realized he was seeing bodies in
orbit around Jupiter-now called Galilean moons-therefore providing evidence to
support Nicholas Copernicus' ideas that not everything in the Solar System
revolved around Earth. In fact, only the Moon does so. All of the major objects
in the Solar System orbit the Sun, and some of these bodies have smaller bodies
orbiting them. These are called satellites.
Galileo's other discoveries such as spots on the surface of
the Sun, geological features on the Moon, the phases of Venus (similar to those
of the Moon), and the multitude of individual stars that made up the Milky Way
provided even further evidence that Earth did not occupy a privileged place in
the Universe. Earth was nothing more than one of many celestial bodies, the one
we happen to know best. Galileo's discoveries went against the doctrine of the
Vatican and the Catholic Church at the time, and in 1633 he was tried by the
Inquisition on suspicion of heresy.
Space observation and exploration technologies have vastly
improved since the days of Galileo. Today, a series of space telescopes and
probes are looking at objects all over the Solar System and the Universe,
missions are collecting images and data of the Galilean moons, space-based Sun
observatories are revealing the structure of the Sun in amazing detail, and
telescopes all over Earth peer deep into the Milky Way and are discovering
planets among its stars.
Notable citizen of Florence
Most Eminent Restorer of Geometry, Astronomy and Philosophy
Comparable to no one in his time"
-Epitaph in Santa Croce, Florence.
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