Welcome back to This Day in History! Back in 1930, February 18 was a day of cosmic significance. Pluto was discovered!

Although some scientists had suspected there was a planet beyond Neptune since before 1905, proper equipment for finding it was not constructed until the late 1920s.

In 1930, Kansas farm boy Clyde Tombaugh verified Pluto’s existence using a fascinating method: he would photograph a patch of sky one day, then photograph it again a few days later. He then used a special detector on the pictures to see if any of the heavenly bodies had changed position since the first photo; planets move at a faster rate than stars, and so if something were in a different place than before, he would know he had found his planet.

Although this method sounds highly laborious, Clyde Tombaugh only had to search for a few months before he found Pluto.

Fun Fact You (Probably) Didn’t Know: The astronomer who first publicly announced Pluto’s discovery was so soft-spoken that very few people heard what he was saying.

Bonus Fact: Pluto is not in fact a planet. It is a dwarf planet, which is quite similar to a planet but much smaller.