Sometimes it’s right under your nose

Neptune was discovered in 1846. But Galileo’s notebooks describe a “star” he saw on 28 December 1612 and 2 January 1613 that we now know was Neptune. Galileo even noticed that his star was in a slightly different location for his two observations, but he chalked the difference up to observational error.

The men who discovered Neptune were not the first to see it; they were the first to realize what they were looking at.