# Galileo's Jupiter Discovery: The Moons That Changed Everything
Published: January 7, 2026
Duration: 2:04
# This is your Astronomy Tonight podcast.
Good evening, stargazers! Today we're celebrating January 7th—a date that marks one of the most dramatic and consequential discoveries in the history of astronomy.
On this day in 1610, Galileo Galilei turned his newly constructed telescope toward Jupiter and made an observation that would shake the very foundations of how humanity understood the cosmos. He discovered **Jupiter's four largest moons**—Io, Europa, Ganymede, and Callisto—now known as the Galilean moons.
Picture this: it's the early 17th century, the Catholic Church has firmly established that everything in the heaven...
Good evening, stargazers! Today we're celebrating January 7th—a date that marks one of the most dramatic and consequential discoveries in the history of astronomy.
On this day in 1610, Galileo Galilei turned his newly constructed telescope toward Jupiter and made an observation that would shake the very foundations of how humanity understood the cosmos. He discovered **Jupiter's four largest moons**—Io, Europa, Ganymede, and Callisto—now known as the Galilean moons.
Picture this: it's the early 17th century, the Catholic Church has firmly established that everything in the heaven...