Staring at the sun—a close (but safe) look at our home star ... a new idea to keep kids entertained? Try stargazing. Free learning activities and videos about the solar system Free learning ...

With a radius of 3,959 miles, Earth is the fifth largest planet in our solar system, and it's the only one known for sure to have liquid water on its surface. Earth is also unique in terms of ...

Since its discovery in 1930, until 2006, Pluto was counted as the ninth planet in the solar system. In 2006, the International Astronomical Union reclassified it as a ‘dwarf planet’, and our ...