well, we don't know yet if he realized it was a planet, although it seems likely. According to the article, he first stumbled across Neptune when it was near Jupiter and later noted its movement.

I love this kind of discovered history! This is kind of like when we discovered that Archimedes was developing calculus.

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"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan