Neptune at Opposition

It’s not often that someone hands an astronomer a major discovery. But that’s what happened 180 years ago today. German astronomer Johann Galle, the director of Berlin Observatory, received a letter from Urbain Le Verrier. The French astronomer had calculated the likely position of a planet beyond Uranus, which at the time was the Sun’s most-distant known planet. Galle looked for the new planet that night – and found it: the planet Neptune. Le Verrier had calculated that Uranus wasn’t orbiting the Sun as expected. He decided that it was being nudged out of position by the gravity of another planet, farther from the Sun. He calculated the planet’s location, then sent his results to Berlin. British astronomer John Couch Adams had made similar calculations. He passed his results to his own colleagues. One of them searched for the planet, and saw it, in 1845 – but he didn’t realize it. So Adams usually is credited as a co-discoverer. But some research in recent years has suggested that his calculations were off, so there’s a debate about who discovered the Sun’s eighth planet. Appropriately enough, Neptune is at its best this week. It lines up opposite the Sun, so it’s closest to Earth, and shining at its brightest. But it’s so far away that you need a telescope to pick it out. It’s not far to the upper right of the bright planet Saturn, which is low in the east at nightfall. More tomorrow. Script by Damond Benningfield