Galileo

Galileo Galilei (1564-1642) was one of the most important early astronomers. He popularised the telescope and was a primary early supporter of the Copernican system of the world.

Galileo built his first telescope in 1609, after hearing of its invention in the Netherlands. He claimed that he deduced how to construct a telescope after only a day of work. Over the course of several years, he built many telescopes for his own use and many to distrubute to friends and colleagues. His first telescope offered a magnification of about eight times, but most of his subsequent observations were made with a telescope that provided a magnification of about twenty times. Some of these telescopes still survive.

It soon became apparent to Galileo that there are more objects in the sky than are possible to see with the human eye alone. He saw stars where none were visible before. He resolved the Milky Way, a cloudy band of light that bridges the sky, into millions of individually faint stars. He also made observations of mountains on the moon, and of four new moons orbiting the planet Jupiter, and of the phasees of Venus.

Galileo used these observations to argue for the Copernican, heliocentric view of the world: that the sun was in the centre of a solar system, and the Earth revolving around it. This was contrary to the generally accepted view at the time, which placed the Earth at the centre of the universe, and the Sun as one of the planets.

Galileo faced a significant challenge in persuading other thinkers of the day to place their confidence in his telescope and observations. The telescope was a difficult tool for some to use, and someone with poor vision might not see any of the things Galileo described. He tried to encourage others to support his work by holding demonstrations. Participants viewed distant details on Earth before observing details in the cosmos above. He also built many other telescopes and sent them to interested parties. He was accustomed to fighting for his ideas. As a court philosopher and mathematician, he frequently engaged in debates about the natural world for the entertainment of observers. He was skilled in rhetorical techniques and made an excellent case for his research. Not everyone who looked through a telescope was instantly convinced, but the telescope's popularity and respect increased over time.