Stars are huge balls of extremely hot, glowing gas. They make their own light and heat. Our Sun is a medium-sized star. It looks so big and bright only because it is much closer to us than any other star.

Stars are so far away that scientists measure their distance in light-years. One light-year is the distance light travels in one year — about 9.5 million million kilometers. The next nearest star after the Sun is over 4 light-years away.

Stars look different in brightness because some are bigger or hotter, and some are closer to us. Stars also have different colors: the hottest stars are blue-white, and the coolest are red. Our Sun is a yellow star.

Long ago, people joined up stars to make pictures called constellations and used them to tell stories, find directions and track the seasons. Because the Earth spins, constellations appear to move across the sky during the night. Because the Earth orbits the Sun, we see different constellations at different times of the year.

Planets do not make their own light. They shine because they reflect sunlight, and they slowly change position against the background stars.