Galileo Galilei, Astronomer/mathematician

Galileo Galilei

Galileo Galilei (Pisa, February 15, 1564 - Arcetri, January 8, 1642), was a Tuscan astronomer, philosopher, and physicist who is closely associated with the scientific revolution. His achievements include improving the telescope, a variety of astronomical observations, the first law of motion, and supporting Copernicanism effectively. He has been referred to as the "father of modern astronomy," as the "father of modern physics," and as "father of science." His experimental work is widely considered complementary to the writings of Francis Bacon in establishing the modern scientific method. Galileo's career coincided with that of Johannes Kepler. The work of Galileo is considered to be a significant break from that of Aristotle. In addition, his conflict with the Roman Catholic Church is taken as a major early example of the conflict of authority and freedom of thought, particularly with science, in Western society.

Early career

Galileo was born in Pisa, Italy, as the son of Vincenzo Galilei, a mathematician and musician.

He attended the University of Pisa, but was forced to "drop out" for financial reasons. However, he was offered a position on its faculty in 1589 and taught mathematics. Soon after, he moved to the University of Padua, and served on its faculty teaching geometry, mechanics, and astronomy until 1610. During this time he explored science and made many landmark discoveries.

Experimental science

In the pantheon of the scientific revolution, Galileo takes a high position because of his pioneering use of quantitative experiments with results analyzed mathematically. There was no tradition of such methods in European thought at that time; the great experimentalist who immediately preceded Galileo, William Gilbert, did not use a quantitative approach. However, Galileo's father, Vincenzo Galilei, had performed experiments in which he discovered what may be the oldest known non-linear relation in physics, between the tension and the pitch of a stretched string. Galileo also contributed to the rejection of blind allegiance to authority (like the Church) or other thinkers (such as Aristotle) in matters of science and to the separation of science from philosophy or religion. These are the primary justifications for his description as "father of science."

In the 20th century some authorities challenged the reality of Galileo's experiments, in particular the distinguished French historian of science Alexandre Koyrй. The experiments reported in Two New Sciences to determine the law of acceleration of falling bodies, for instance, required accurate measurements of time, which appeared to be impossible with the technology of the 1600s. According to Koyrй, the law was arrived at deductively, and the experiments were merely illustrative thought experiments.

Later research, however, has validated the experiments. The experiments on falling bodies (actually rolling balls) were replicated using the methods described by Galileo (Settle, 1961), and the precision of the results was consistent with Galileo's report. Later research into Galileo's unpublished working papers from as early as 1604 clearly showed the reality of the experiments and even indicated the particular results that led to the time-squared law (Drake, 1973).

Astronomy

Although the popular idea of Galileo inventing the telescope is inaccurate, he was one of the first people to use the telescope to observe the sky. Based on sketchy descriptions of telescopes invented in the Netherlands in 1608, Galileo made one with about 8x magnification, and then made improved models up to about 20x. On August 25, 1609, he demonstrated his first telescope to Venetian lawmakers. His work on the device also made for a profitable sideline with merchants who found it useful for their shipping businesses. He published his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Sidereal Messenger).

It was on this page that Galileo first noted an observation of the moons of Jupiter. Galileo published a full description in Sidereus Nuncius in March 1610.

On January 7, 1610 Galileo discovered three of Jupiter's four largest satellites (moons): Io, Europa, and Callisto. Ganymede he discovered four nights later. He determined that these moons were orbiting the planet since they would occasionally disappear; something he attributed to their movement behind Jupiter. He made additional observations of them in 1620. Later astronomers overruled Galileo's naming of these objects, changing his Medicean stars to Galilean satellites. The demonstration that a planet had smaller planets orbiting it was problematic for the orderly, comprehensive picture of the geocentric model of the universe, in which everything circled around the Earth.

Galileo noted that Venus exhibited a full set of phases like the Moon. The heliocentric model of the solar system developed by Copernicus predicted that all phases would be visible since the orbit of Venus around the Sun would cause its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and to face away from the Earth when it was on the Earth-side of the Sun. By contrast, the geocentric model of Ptolemy predicted that only crescent and new phases would be seen, since Venus was thought to remain between the Sun and Earth during its orbit around the Earth. Galileo's observation of the phases of Venus proved that Venus orbited the Sun and lent support to (but did not prove) the heliocentric model.

Galileo was one of the first Europeans to observe sunspots, although there is evidence that Chinese astronomers had done so before. The very existence of sunspots showed another difficulty with the perfection of the heavens as assumed in the older philosophy. And the annual variations in their motions, first noticed by Francesco Sizzi, presented great difficulties for either the geocentric system or that of Tycho Brahe. A dispute over priority in the discovery of sunspots led to a long and bitter feud with Christoph Scheiner; in fact, there can be little doubt that both of them were beaten by David Fabricius and his son Johannes.

He was the first to report lunar mountains and craters, whose existence he deduced from the patterns of light and shadow on the Moon's surface. He even estimated the mountains' heights from these observations. This led him to the conclusion that the Moon was "rough and uneven, and just like the surface of the Earth itself", and not a perfect sphere as Aristotle had claimed.

Galileo observed the Milky Way, previously