Alpha Centauri, a system of three stars, one of whose membersProxima Centauriis the star nearest the sun. Proxima can be seen only with a telescope; the other two stars appear as a single, very bright star to the unaided eye. Alpha Centauri is slightly more than four light-years from the sun. It is in the constellation Centaurus.
A billion years ago, the moon stopped being geologically active. But that's not to say that the moon is doing nothing for us. Let's find out why we owe our moon some thank-yous.
Neptune is the eighth planet from the sun, the fourth largest, and a gas planet. It is named after the Roman god of the sea. Neptune is four times the size of Earth, and its day lasts a little more than16 hours. Its year is about 165 Earth years. Neptune's orbit is a perfect circle. The last stop on spacecraft Voyager's epic trip through the solar system was the gas giant Neptune.