The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

NASA first thought that Eris was bigger than Pluto, and they originally described Eris as the 10th planet in the solar system. But the International Astronomical Union, or IAU, wasn't too thrilled ...

There are eight official planets (sorry, Pluto) in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. But astronomers have spent the better part of a century ...

Mercury takes only 88 Earth days to orbit the sun.

All seven of the other planets in our solar system are about to become visible at once in a great planetary alignment – ...