... Historical Data . Orbital Data . Physical Data . ... Sun . ... Jupiter . ... Saturn . ... William Herschel . ... William Cranch Bond . ... William Henry Pickering . Uranus . ... 1986 . Voyager 2 . ... William Lassell . ... J. Christy Key: Name Name of the planet or satellite. Orbits Sun or planet about which it orbits. ...

... Neptune is smaller in diameter but larger in mass than Uranus . ... N eptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. ... A t the time of the Voyager encounter, Neptune's most prominent feature was the Great Dark Spot (left) in the southern hemisphere. ... Neptune's winds blew the Great Dark Spot westward at 300 meters/second (700 mph). ... L ike Uranus and Jupiter, Neptune's rings are very dark but their composition is unknown. ... Neptune's Ring System . ... Uranus .. ...

... Auroral Currents . ... 25b. Io Dynamo . ... Aurora from Space . ... The giant planet Jupiter has four large moons, discovered by Galileo and visible through good binoculars. ... A dynamo is created in a magnetic field by an electric circuit, part of which is moving relative to the rest (additional conditions must also be met). ... Furthermore, the plasma between them conducts electricity very well along its magnetic field lines, which act as if they were wires connecting Io and the planet (drawing)....