Discovered on today’s date: ‘Planet X’

Pluto’s existence had actually been theorized for decades since Percival Lowell began to suspect that deviations in the positions of Uranus and Neptune could be caused by the severity of a ninth planet covered at that time. Lowell looked through millions of constellations for years and searched for a weak point among many. When he died, he decided in his will that the hunt for Planet X (as it was then called) should continue at the observatory that was called.

Tombaugh, who had not even been born when Lowell started his search for Planet X, discovered Pluto when he compares two photographic plates that were six days apart in the previous month. He noticed a tiny spot that had changed the position between the two shots.

This segment originally appeared in today’s edition of The Morning letter newsletter. Register here To get from the weather channel and our meteorologists on weekdays.

Senior writer Chris Deweese Edits Morgenbrief, The weekday newsletter of Weather Channel.