A planetarium is a special theater with a domed ceiling where you can watch shows about space, stars, and planets. Instead of a flat movie screen, the entire ceiling becomes the night sky. Powerful projectors create realistic images of stars, constellations, planets, and galaxies all around you, making you feel like you're floating in space.

Modern planetariums can show you what the night sky looked like thousands of years ago, or what it will look like in the distant future. They can take you on journeys to distant galaxies, show you what it's like to stand on Mars, or help you understand how eclipses work.

When you visit a planetarium, you sit in a seat that tilts back so you can comfortably look up at the dome. The lights dim, and suddenly you're surrounded by stars. A narrator might guide you through the constellations, explaining which bright dot is actually Jupiter or how to find the Big Dipper. Some planetariums also have exhibits with meteorites, telescopes, and hands-on displays about astronomy.

The word can also refer to the projector itself, which creates all those stars and planets on the ceiling.