On Today's Date: 'Planet X' Discovered

On today’s date 95 years ago, everyone’s favorite not-quite-a-planet, Pluto, was discovered by astronomer Clyde W. Tombaugh while working at the Lowell Observatory in Flagstaff, Arizona.

Pluto’s existence had actually been theorized for decades previously, ever since Percival Lowell started suspecting that deviations in the positions of Uranus and Neptune might be caused by the gravity of a then-undiscovered ninth planet. Lowell spent years sifting through millions of star images, looking for one dim dot among many. When he died, he decreed in his will that the hunt for Planet X (as it was then called) should continue at the observatory that bore his name.

Tombaugh, who hadn't even been born yet when Lowell started his search for Planet X, discovered Pluto when he was comparing two photographic plates that had been taken six days apart during the previous month. He noticed a tiny speck that had changed position between the two shots.

This segment originally appeared in today's edition of the Morning Brief newsletter. Sign up here to get weekday updates from The Weather Channel and our meteorologists.

Senior writer Chris DeWeese edits Morning Brief, The Weather Channel’s weekday newsletter.