Light travels at 186,000 miles per second. The Sun is so far away from us that it takes the light leaving its surface 8 minutes to reach Earth. If the Sun suddenly blew up, would we know about it right away? Why? Sirius, a star in the constellation Canis Major, is the brightest star in the sky. It is about 50,000,000,000,000 miles away. Light travels 186,000 miles per second. How long does it take light from Sirius to reach Earth? A rainbow in the sky is a spectrum. To unscramble Sunlight into a spectrum, you need a prism. What acts as a prism in the air that makes a rainbow?