Galileo's Astronomical Discoveries

Galileo's Astronomical Discoveries

Overview

This lecture covers Galileo Galilei’s life, his contributions to astronomy, his use of the telescope, and the impact and resistance to his heliocentric discoveries.

Galileo Galilei: Background

• Galileo is one of the most famous historical scientists, commonly known by his first name.
• His full name is Galileo Galilei.
• He lived during a time when astronomy was done with the naked eye.

The Telescope and Its Invention

• Galileo is often credited with inventing the telescope, though a watchmaker may have created a similar device first.
• The crucial innovation was using the telescope to observe the sky rather than just objects on Earth.
• Galileo’s astronomical observations included the Moon, planets, stars, and even the Sun (which may have led to his blindness).

Key Astronomical Discoveries

• The Moon: Galileo observed craters, mountains, and valleys similar to Earth, showing the Moon is a physical place like Earth.
• The Planets: He discovered planets are not stars but have Earth-like characteristics, challenging the idea that Earth is unique.
• Moons of Jupiter: He found four moons orbiting Jupiter, proving that not everything orbits Earth.
• Phases of Venus: Galileo observed Venus showing different phases and changing size, which can only be explained if Venus orbits the Sun. This provided direct evidence for heliocentrism.

Reaction and Aftermath

• Despite clear evidence, Galileo’s discoveries were not accepted and he was placed under house arrest for life.
• His family was also punished to suppress his bloodline.
• The Catholic Church, along with other groups, rejected his findings.
• The Church formally apologized for their treatment of Galileo in the 1990s, long after the heliocentric model was accepted.

Key Terms & Definitions

• Heliocentrism — The model where planets orbit the Sun.
• Telescope — An instrument that magnifies distant objects, crucial for Galileo’s discoveries.
• Phases of Venus — The changing shapes and apparent sizes of Venus as seen from Earth, proving it orbits the Sun.
• Epicycle — A small circular orbit used in the geocentric model to explain planetary motions.

Action Items / Next Steps

• Review Galileo’s main telescope discoveries and their significance.
• Understand why the phases of Venus are proof of heliocentrism.
• Prepare for questions on the historical resistance to Galileo’s findings.