�[The universe] cannot be read until we have learnt
the language and become familiar with the characters
in which it is written. It is written in mathematical
language, and the letters are triangles, circles and
other geometrical figures, without which means it is
humanly impossible to comprehend a single word.�
(Galileo, Opere Il Saggiatore, p. 171.)
Galileo Galilei was born on February 15, 1564 in Pisa, Italy. As a young man, Galileo was very interested in astronomy and natural philosophy. He studied medicine at the University of Pisa because his father wanted him to be a medical doctor, but then, while ditching his classes one day, he overheard two math professors talking. Realizing that medicine wasn�t really the path he wanted to take, Galileo instead began to study mathematics, which led to him his job as a private teacher in Florence in 1989, then as a professor at the University of Pisa.
In 1592, because of quarrels with his colleagues, Galileo left for the University of Padua. He was soon promoted to professor of mathematics, his job mainly to teach Euclid�s geometry. He also taught standard astronomy to some medical students at the university, because they needed the knowledge in order to use astrology effectively in their medical practice. Then, in a public lecture about the appearance of a �new star� (which is now known as the �Kepler�s supernova�), Galileo made a mistake. He apparently discussed more unconventional forms of astronomy and natural philosophy, which later led to a letter he wrote to Kepler, whom he�d become good friends with, in 1598. In this letter, Galileo said that he believed in Copernicus�s theory that the Earth traveled around the sun.
In the summer of 1609, he heard about a spyglass that a Dutchman had recently invented, which was being shown in Venice, Italy. An idea began to form in his mind, so he began to experiment. Because of his knowledge of mathematics, Galileo soon made telescopes whose ability surpassed those of the Dutchman�s spyglass. While using his telescopes, he was very surprised to find that the moon has mountains. He was also amazed when he saw four objects orbiting Jupiter. Because he was trying to get a job in Florence, he named the moons after a powerful family in Italy, calling them �the Medicean stars.� Soon, a short book was published in 1610 called Message from the Stars. A man in Florence heard of his findings, so Galileo did end up getting a job in Florence, as the mathematician and natural philosopher for the Grand Duke of Tuscany. This was also the year when he began studying sunspots. In 1613, he began observing Saturn and Venus with his telescope. He discovered that the planet Venus has phases like the moon, which, he concluded, meant that it orbited around the sun, not the earth. Galileo gradually began to lecture about his findings and join debates. He defended Copernicus�s theory about a heliocentric universe, and got into heated arguments with many of his fellow astronomers. He began making enemies with many people, mostly those who believed in the Tychonic theory.
Galileo then invented the microscope, between the year 1619 and 1624. He called it an occhialini, and it was made of a smaller version of a telescope tube, with two lenses. He gave this invention to various people, including a close friend named Federigo Cesi, who over the years, had supported his ideas. Cesi was close friends with the man who decided on the name �microscope.� In 1623, Galileo wrote The Assayer, also known as Saggiatore, which is focused on the nature of comets. Galileo thought that comets are optical illusions caused by the refraction of sunlight as it comes through the atmosphere.
Pretty soon, because of his beliefs in the Copernicus theory, he was accused of going against the doctrine of the Church, which ended with him making enemies with the Roman Catholic Church. In the year 1616, Galileo was given a secret, but official, warning that he was not to defend Copernicanism. He evidently went against this warning when he wrote his book called Dialogue Concerning the Two Greatest World Systems, which was smuggled to Italy for publication in 1632. By this time, Galileo had failing health, and when he was sentenced to house arrest in Rome, there was nothing really he could do about it. Although he was basically condemned to his villa, he did not let this stop him from making further discoveries. In the year 1638, he invented what he called the thermoscope, which is like a modern day thermometer, and wrote a handbook telling how to use it. Soon after, though, Galileo went blind. He died on Jan 8, 1642 in Arcetri, the year Isaac Newton was born.
Over the years, Galileo had made many other important discoveries. For instance, he once decided that he would prove Archimedes wrong. The theory was that objects of different weights would fall at different speeds. Galileo dropped two balls from the tower of Pisa. Both landed at the same time. Also, using his famous moons of Jupiter, Galileo developed a way to measure longitude and latitude at sea. He made a design for a machine that would raise water levels, powered by horses and a single wooden bar. He experimented with lodestones, trying to prove that their magnetism could be strengthened, and he made a model of the inclined plane.
Galileo made many important discoveries in the field of science throughout his lifetime. If it wasn�t for him, we wouldn�t have the thermometer, the telescope, the compass, the knowledge that the solar system isn�t geocentric, and many more important bits of knowledge. Even though Galileo Galilei was considered crazy at his time, accused of going against the Scripture, he was still a great man, and will always be remembered.
Links:
1. http://loeningen.jteln.de/privat/p_niester/p_natwis/galileo_galilei/index.html
2. http://galileo.imss.firenze.it/museo/b/egalilg.html