Pluto's days, though they drag on a bit at around 153 hours, are nothing compared to its years. Pluto's orbit takes 248 Earth ...

Pluto sits far out in the Solar System, small and dim, moving at a pace that barely fits human timelines. It was found in ...

(Correction: An earlier version of this story misstated how far Pluto is from the sun. The correct number is 3.7 billion miles.) What was discovered in Flagstaff, Arizona, and killed off in Prague? If ...

FLAGSTAFF – Clyde Tombaugh sat in the Orpheum Theater that fateful night in February 1930, waiting for clouds to pass before the 24-year-old astronomer could return to Lowell Observatory to confirm ...

Pluto may have been demoted to non-planet status, but it still commands a court of five moons, as is fitting for the king of darkness; after all, Pluto is the Roman equivalent of the Greek God Hades.

On January 5, 2005, astronomers at NASA discovered Eris, the second-largest dwarf planet in the solar system. Eris is just ...