NHAS - Today in Astronomy History

1846

Neptune discovered. Neptune was first predicted by English astronomer John Adams based on his calculations of anomalies in the orbit of Uranus. He attempts to bring this to the attention of Sir George Airy, the Astronomer Royal at Greenwich, to have a search begin, but this never happens due to a series of social and political mishaps. In the meantime, French mathematician Urbain Le Verrier independently arrives at similar calculations and publishes them. Upon reading Le Verrier's paper, Airy directs James Challis, Director of the Cambridge Observatory, to begin a search immediately. Challis records the position of Neptune on several nights, but he fails to compare the right charts and the planet goes unnoticed. Back in France, Le Verrier has trouble convincing French authorities that a search is worthwhile, so he sends his predicted position to astronomer Johann Galle, an acquaintance at the Berlin Observatory. Using a new star chart, Galle sights Neptune after only 30 minutes effort. The French immediately claim the discovery, despite the observation having been made in Germany. The British claim the credit should go to Adams, whose prediction had been just as close as Le Verrier's and made more than a month earlier. After the orbit is determined a search of previous works shows that French astronomer Joseph Lalande had recorded Neptune on a star chart in May, 1795 but failed to realize it was a planet. In 1980, a search of Galileo's notebooks showed that he recorded the position of Neptune in 1612 and 1613 but hadn't noticed that it moved relative to the stars - he thought it was just another star. Today, Adams and Le Verrier are jointly credited with the discovery, although some give that honor to Galle.