# Galileo's Jupiter Discovery: Four Moons Change Everything
Published: January 13, 2026
Duration: 1:37
# This is your Astronomy Tonight podcast.
Good evening, stargazers! Today, January 13th, marks a truly momentous occasion in our cosmic calendar—the anniversary of one of the most thrilling discoveries in planetary science!
On this date in 1610, the legendary Galileo Galilei turned his primitive telescope toward Jupiter and witnessed something that would forever change humanity's understanding of the universe. He discovered the four largest moons of Jupiter—what we now call the Galilean moons: Io, Europa, Ganymede, and Callisto.
Can you imagine the shock? Here was Galileo, peering through his handmade optical tube, expecting to s...
Good evening, stargazers! Today, January 13th, marks a truly momentous occasion in our cosmic calendar—the anniversary of one of the most thrilling discoveries in planetary science!
On this date in 1610, the legendary Galileo Galilei turned his primitive telescope toward Jupiter and witnessed something that would forever change humanity's understanding of the universe. He discovered the four largest moons of Jupiter—what we now call the Galilean moons: Io, Europa, Ganymede, and Callisto.
Can you imagine the shock? Here was Galileo, peering through his handmade optical tube, expecting to s...