Somebody still had to draw the map
23 September 1846, Berlin. Johann Galle points a telescope where Urbain Le Verrier's arithmetic says a planet must be. Inside an hour, student Heinrich d'Arrest looks up from a star chart: “That star is not on the map.”
The kept story is that mathematics found a planet. The record keeps more.
Britain had it first. James Challis at Cambridge swept that part of the sky twice that August, logged Neptune as a star, and only understood what he had seen after Berlin announced it. His charts were out of date. The standard accounts cannot even agree on which two dates.
And the thing that made the find was not the telescope. It was Hora XXI, a star chart finished in 1844, printed in 1845, still undistributed because the rest of the series was not ready. Without the map, the star was just a star.
Arago said Le Verrier discovered a planet “with the point of his pen.” True. Somebody still had to draw the map.