Video narration
What if the Solar System were not a row of worlds, but a neighborhood in motion? At its center is the Sun, our star, with eight very different neighbors. Closest to farthest, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The four inner planets are small, rocky worlds. Farther out, the four outer planets are much larger, made mostly of gas or ice. So this is not a neighborhood of matching houses-or matching balls. Each planet travels around the Sun along its own path, called an orbit. They do not sit still; they are always moving, often at different speeds. Why do they stay together instead of flying away? Gravity-the Sun's pulling force-keeps them in orbit. So the answer is this: our moving neighborhood, centered on the Sun and held by its gravity, is the Solar System.