NEPTUNE WAS DISCOVERED AS THE RESULT of calculations. By the early 19th century, astronomers realized that Uranus was not following its expected orbit.The gravitational pull of an unknown planet beyond Uranus seemed the most likely explanation. In 1845,the English mathematician John Couch Adams (1819-1892) announced that he had calculated the probable position of a planet beyond Neptune, but his findings were ignored. In June 1846,the Frenchman Urbain LeVerrier did the same. This time, observers took notice. Johann Galle (1812-1910) of the Berlin Observatory found Neptune on September 23, 1846.Astronomers continued to speculate about another planet beyond Neptune.

NEPTUNE'S RINGS: Neptune, like all the giant planets, has a series of rings enCircling it. The rings were discovered when the planet passed in front of a star. Results of an occultation (p.55) in July 1984 showed the typical "blinking on and off,"indicating that Neptune's rings were blocking out the light of the distant star. There seem to be two main rings, with two faint inner rings. The inner ring is less than 9 miles (15 km) wide. The rings were confirmed by Voyager 2 in 1989.

NEPTUNE'S VANISHING GREAT DARK SPOT: In 1989 Voyager photographed a great storm system in Neptune's southern hemisphere. The storm, actually a hole in Neptune's upper cloud layer, was about the size of Earth. Smaller clouds at the edges of the hole in this sequence-taken over a four-day period-suggested that the storm rotated counterclockwise. However, in the photographs taken of Neptune by the Hubble SpaceTelescope in 1995,the storm had disappeared.