Tuesday, February 26, 2008

Understanding Galileo's Work

While Kepler was theorizing from Copernicus’s data, an Italian astronomer, Galileo Galilei (1565–1642), directed his gaze skyward, amplifying his eyesight with the aid of a new Dutch invention (which we’ll meet in the next chapter), the telescope. Through this instrument, Galileo explored the imperfect surface of the moon, covered as it was with craters, “seas,” and features that looked very much like the surface of the earth. Galileo was even more surprised to find that the surface of the sun was blemished. These “sunspots”, he noted, changed position from day to day. From this fact, Galileo did not conclude that the spots changed, but that the sun was rotating, making a complete revolution about once each month.

His telescope also revealed for the first time that moons orbited Jupiter—another observation that strongly supported the notion that the earth was not the center of all things. He observed that the planet Venus cycled through phases, much like the moon, and that the size of the planet varied with its phase. From this, he concluded that Venus must orbit not the earth, but the sun.

Galileo published these many independent experimental proofs of a heliocentric solar system in 1610.Six years later, the Catholic Church judged the work heretical and banned them, as well as the work of Copernicus. Galileo defied the ban and, in 1632, published a comparison of the Ptolemaic and Copernican models written as a kind of three-way discussion. He was so bold as to write in Italian, instead of learned Latin, which meant that common folk (at least those who were literate) were being invited to read a theory that challenged the teaching of the Church.

Galileo was silenced by the Holy Inquisition in 1633, forced to recant his heresy under threat of death, and placed under house arrest for the rest of his life.

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