| Galileo was born in Pisa in 1564. He studied at the University of Pisa, where he was appointed to the chair of
mathematics in 1589. It was at this point that Galileo began to express criticisms of various parts of the
Aristotelian natural philosophy being taught. His laws of falling bodies are the best known symbol of his
dissatisfaction. Soon Galileo moved to the chair of mathematics at Padua, where he remained until 1610.
Galileo's observations of and public lectures on the nova of 1604 first gave him a reputation as an astronomer.
Until this point he had been known as a mathematician. In the absence of observable parallax, the nova indeed
appeared to be a new star. Galileo lectured on the difficulties with the Aristotelian idea of the immutability
of the heavens arising from this fact. In 1610 Galileo was appointed mathematician to the Grand Duke of
Tuscany, and he returned to Florence.
Much of Galileo's most important astronomical work dates from the 1610s. It was in the January of 1610 that
Galileo first observed the four "Galilean" satellites of Jupiter. This was problematical for the
anti-Copernicans, as it suggested there were centres of rotation in the Universe other than the Earth. A little
more than a year later, Galileo was able to distinguish between the satellites, and hence determine their
periods of revolution.
Before the end of 1610, Galileo had observed that Saturn appeared non-circular, although he could not resolve
the rings, and thought them to be satellites revolving very close to the planet. Galileo's observations of the
phases of Venus posed severe problems for the Ptolemaic model of the Universe, which could not account for all
of the observed phases.
Galileo also attempted to solve the infamous problem of determining longitude at sea (the eventual solution of
this problem is described in the excellent Longitude by Dava Sobel - who is also the author of
Galileo's Daughter, I believe). He proposed the use of the Jovian satellites as a sort of Universal
clock, by the use of a device he had designed, and tables of eclipses of the Satellites. He failed to collect
the 25,000 florins prize offered by the Stadholder of the Netherlands for the solution of the Longitude problem.
In 1632 Galileo published the Dialogue Concerning the Two Chief World Systems, the Copernican and the
Ptolemaic. This book was written as a series of discussions between three people: Salviati (representing
Galileo); Sagredo (an intelligent listener); and Simplicio (a dull-witted Aristotelian). As the Dialogue
was written in this popular style, it was much more widely accessible than previous books on Copernicanism had
been, and so attracted the attention of the Holy Office. Galileo was summoned to Rome, where a tribunal of
seven Cardinals required Galileo to solemnly abjure his theory, and sentenced him to house arrest in Arcetri.
Galileo's health deteriorated - by 1638 he was completely blind. He died on 8th January 1642.
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