Space weather is how the environment around the Earth and solar system may vary because of activity at the sun. The Northern Lights is a harmless example of space weather. It is an effect of an event called a Coronal Mass Ejection or CME.
Scrat accidentally enters a flying saucer and propels himself into outer space. He travels through the solar system (also by accident), and during his journey finds a solar system, planets, asteroids, and other celestial objects.