the discovery of a new planet. The search for Pluto did not begin with Clyde Tombaugh, to be fair. That distinction belongs to the visionary astronomer Percival Lowell. In 1894, Lowell founded ...

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 ...

For one reason or another, some people are still upset about Pluto's demotion from planet to dwarf planet. This demotion, by the way, occurred all the way back in 2006. So, what does famed ...

Pluto failed to meet that third criterion, so it was reclassified as a “dwarf planet” on Aug. 24, 2007. Critics point out that by that criterion, the Earth is also not a planet: We constantly ...

The International Astronomical Union reclassified Pluto as a dwarf planet because it does not clear its orbit of other debris. Pluto was the little planet that could — until it couldn’t.

Not every talk at ... 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-is-a-planet holdout ...

Pluto did not meet all three criteria the IAU determined were necessary to be considered a planet: The body must orbit its host star, just as Earth and Jupiter orbit the sun. It is large enough to ...

If you grew up learning that Pluto was a planet, chances are you were sticking to that, no matter what the IAU said. After all, it's not like anyone had truly seen Pluto before New Horizons ...