If you answered "Pluto's planethood," your grasp of the astronomical is excellent. Feb. 18 marks the 95th anniversary of the discovery of our outermost planet-not-planet. Here's what to know about ...

A stunning planet parade is now visible in the night sky. A planet parade is when several of our solar system's planets are visible in the night sky at the same time. All seven planets will be visible ...

He called this hypothetical world "Planet X." "In some ways, Pluto's more of a planet than some of the other established planets, like Mercury." ...

Viewed in this longer context, the previously modern idea of having nine planets, which came about in the 1960s and lasted only until 2006, was a blip on the screen. And if you are still a Pluto ...

Clyde Tombaugh discovered Pluto in 1930 at Lowell Observatory in Flagstaff. Here's how Pluto won - and lost - its planetary ...