I love the discovery of Pluto. For my money its the single least probable thing to happen in the history of humanity - and I mean that.

Rewind to when Uranus was the farthest known planet from the Sun. An astronomer took a look at the orbits and masses of all known planets, and found that Uranus wasn't quite in the orbit that it was supposed to be. But if you add another planet of about the same size at a particular place in a particular orbit, now Uranus' orbit makes sense. Another astronomer looked through a telescope at that particular place in the sky and discovered Neptune.

A while later another astronomer did something similar, and found that Neptune's orbit didn't make sense either. But if you placed another Earth sized at a particular place in a particular orbit now Neptune's orbit makes sense. So Kershaw's uncle looked through a telescope at a particular spot in the sky and found Pluto, which was then assumed to be about Earth sized.

Further observations showed that Pluto wasn't Earth sized, it was about 1/10 the size of Earth. Further observations showed that it was actually 1/100 the size of Earth. Further observations showed that it was less than 1/500 the size of Earth, way smaller than tons and tons of moons, and a few asteroids besides. So astronomers went back and rechecked the math of the guy who predicted the Earth sized Pluto based on Neptune's orbit, and found that he had made a mistake. Neptune's orbit was fine, and there's no need for Pluto for it to make sense.

So the discovery of Pluto was entirely coincidental. Lowell (who predicted Pluto's orbit) may as well have just pointed to a random spot in the sky, saying "If you look there you'll find something in the solar system", and when astronomers looked there there was. The sky contains 12960000 square arc seconds, and Pluto takes up 0.004225 square arc seconds, meaning there was a 0.000000032600309% chance that Kershaw's great uncle would see something when he looked through that telescope, but he did and what he saw was Pluto