Rediscovering Galileo

In this episode, Rediscovering Galileo . . .

Today, we’re turning our telescopes back in time to explore Galileo Galilei's work and how amateur astronomers today can experience his groundbreaking discoveries for themselves.

If you listened to last week's podcast, Planetary Pursuit, you might have heard me say that Jupiter is “my favorite planet." Here’s why–

Galileo’s Dialogue Concerning the Two Chief World Systems, published in 1632, challenged the geocentric model of the universe—the belief that everything orbits around Earth. Instead, he advocated for the Copernican model, which places the Sun at the center of our solar system. This book was not just a scientific treatise but also a revolutionary act that put Galileo in conflict with the Catholic Church.

Galileo presented his arguments as a dialogue between three characters: Salviati, who supported the heliocentric model; Simplicio, who defended the traditional geocentric view; and Sagredo, an open-minded observer. It’s easy to see who emerged looking a bit foolish. Simplicio, perceived as representing Church doctrine, was portrayed as less informed, leading to accusations that Galileo mocked the Church's authority.

In 1633, Galileo was tried by the Inquisition, forced to recant his support for heliocentrism, and placed under house arrest. The Catholic Church had declared heliocentrism heretical in 1616, leading to his confinement. The Inquisition found him "vehemently suspect of heresy" for supporting the Copernican system and pressured him to retract his views publicly, which he refused. Galileo spent the remainder of his life under house arrest, where he continued his scientific work.

Despite the controversy, Galileo’s observations were difficult to refute. Let’s begin with one of his most famous: Jupiter and its moons. In 1610, Galileo discovered four moons orbiting Jupiter using his enhanced (20X) telescope. Today, we call them the Galilean moons: Io, Europa, Ganymede, and Callisto.

By tracking their movements night after night, Galileo demonstrated that these moons orbited Jupiter, not Earth. This was significant because it proved that not everything in the cosmos revolves around us. It was akin to discovering a mini solar system, providing strong evidence for the Copernican model.

It wasn’t until 1992 that Pope John Paul II formally pardoned Galileo, acknowledging the Church’s error in condemning his findings and praising his scientific contributions.

And here’s the fun part: You can repeat Galileo’s observations using a simple telescope. Just point it at Jupiter on a clear night. Over several evenings, you’ll notice the positions of its moons shift—evidence that they’re orbiting the gas giant. Here are a few hand-drawn diagrams and notes from my version of his experiment.

Galileo didn’t stop with Jupiter. He observed the phases of Venus, which change similarly to the Moon’s phases. This wouldn’t be possible if Venus orbited Earth. Instead, it only makes sense if Venus orbits the Sun, reinforcing the heliocentric model.

With a telescope, you can observe the phases of Venus yourself. It’s an incredible way to connect with the scientific revolution that Galileo helped ignite. And don’t forget his work with the Moon! Galileo’s sketches of craters and mountains shattered the belief that celestial bodies were perfect spheres. Grab some binoculars or a small telescope and look at the Moon during its crescent phase for stunning shadows and details.

So, whether it’s Jupiter’s moons, Venus’s phases, or the rugged surface of the Moon, Galileo’s discoveries are accessible to anyone with curiosity and a telescope. Why not step into his shoes and see the universe as he did. An amateur astronomer's way to step back in time.

I’m Patrick Ball. Thanks for listening, and I’ll see you in the next episode.