Betelgeuse, a bright reddish star in the constellation Orion. It is about 495 light-years from the earth, though some measurements put it at about 640 light-years away. Its color indicates a relatively low surface temperature of about 5,000° F. (2,800° C.), about half that of the sun. Betelgeuse is a variable star that fluctuates irregularly in size and brightness. At its smallest, Betelgeuse has a diameter some 300 times that of the sun; its greatest diameter is about one-third larger than this. Betelgeuse is classified in the group of largest known stars, the supergiants.
Since the 19th century, humans have wondered about the prospect of life on Mars. While we haven't sent anyone to the Martian surface, we have sent spacecrafts, which have gathered a good amount of information on what it's like on Mars. How is it different from Earth? How is it similar? And could life really have existed there long ago, or exist in the future?
The moon is often the largest object in the sky outside of the sun. What is the moon made of, how did it form -- and why do people blame it for their strange behavior?