Clyde Tombaugh didn't set out to discover Pluto when he sent his sketches of the night sky to Lowell Observatory in Flagstaff ...

Earth has a newly-discovered neighbor in the solar system. But the heavenly body – possibly a dwarf planet à la Pluto – isn't a frequent visitor. Located beyond Neptune, its extreme orbit ...

What was discovered in Flagstaff, Arizona, and killed off in Prague? If you answered "Pluto's planethood," your grasp of the astronomical is excellent. Feb. 18 marks the 95th anniversary of the ...

After passing in the state senate, a new bill that would officially designate Pluto as Arizona's state planet is now at the will of Gov. Katie Hobbs. Since its discovery in Flagstaff, Pluto has become ...

The year was 2015. After traveling billions and billions of miles through the Erebus, New Horizons encounters the boatman, and the somber lord of the departed. The spacecraft could have been called ...

The planet Neptune wobbled in its orbit around the Sun. That could only mean one thing, astronomers said: There was a ninth planet out there, somewhere, lurking in the fringes of the solar system.

Pluto, discovered in 1930, was once considered the ninth planet in our solar system. In 2006, the International Astronomical Union reclassified Pluto as a dwarf planet because it doesn't meet all the ...

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The planet in the cornfield -- Fellow wanderers -- The search for planet X -- Pluto and its little pals -- The meaning of a moon -- There goes the neighborhood -- Not yet explored -- Betting on the ...

For decades, Pluto was celebrated as the ninth planet of our solar system. However, in 2006, the International Astronomical Union (IAU) redefined what constitutes a planet, leading to Pluto’s ...

(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 ...