Monitoring the Sun with Neptune
On the night of September 23, 1846, German astronomer Johann Gottfried Galle called out the configurations of stars in the field of view of the 9-inch refractor at the Berlin Observatory, while an assistant, Heinrich Louis d’Arrest, checked them on a map. Just after midnight, Galle called out that a star of 8th magnitude was in a particular location. D’Arrest immediately exclaimed: “That star is not on the map!”
That “star,” of course, was a new planet, Neptune. Although a giant planet with an equatorial diameter almost four times larger than
