Galilean Moons

Hello there. We are four best friends who love to dance in the big, dark sky. We spin and twirl and play hide-and-seek with our giant, stripey dance partner. Do you know who it is. It's Jupiter. We are Jupiter's biggest moons. Our names are Io, Europa, Ganymede, and Callisto. We love playing together. People on Earth call us the Galilean Moons, and we are so happy to meet you.

For a very, very long time, we were a secret. No one on Earth knew we were here, dancing so far away in the quiet sky. But one night, a man named Galileo Galilei pointed a special looking-glass, called a telescope, toward our giant friend Jupiter. It was a chilly night on January 7th, 1610. Peeking through his telescope, he saw us. At first, he thought we were tiny, sparkly stars. But he was a very curious man, so he watched us for a few more nights. He saw that we weren't staying still—we were dancing around Jupiter, just like we always do. He was so excited. He was the very first person to see moons playing with another planet.

Seeing us was a big surprise for everyone on Earth. It was a wonderful secret revealed. It showed them that not everything in the universe circled the Earth. It was a brand-new idea that made people think about the sky in a whole new way and wonder what other secrets were out there. We are still out here, spinning and twirling around our big friend Jupiter. So the next time you look up at the night sky, remember us and our happy dance. There are so many wonderful, sparkling secrets in the universe, just waiting for you to discover them.