Uranus Cloud Movement

Time-lapse Voyager 2 images of Uranus show the movement of two small, bright, streaky clouds -- the first such features ever seen on the planet. The clouds were detected in this series of orange-filtered images taken Jan. 14, 1986, over a 4.6-hour interval (from top to bottom). At the time, the spacecraft was about 12.9 million kilometers (8.0 million miles) from the planet, whose pole of rotation is near the center of each disk. Uranus, which is tipped on its side with respect to the other planets, is rotating in a counterclockwise direction, as are the two clouds seen here as bright streaks. (The occasional donut-shaped features that show up are shadows cast by dust in the camera optics. The processing necessary to bring out the faint features on the planet also brings out these camera blemishes.) The larger of the two clouds is at a latitude of 33 degrees; the smaller cloud, seen faintly in the three lower images, lies at 26 degrees (a lower latitude and hence closer to the limb). Their counterclockwise periods of rotation are 16.2 and 16.9 hours, respectively. This difference implies that the lower-latitude feature is lagging behind the higher-latitude feature at a speed of almost 100 meters per second (220 mph). Latitudinal bands are also visible in these images. The faint bands, more numerous now than in previous Voyager images from longer range, are concentric with the pole of rotation -- that is, they circle the planet in lines of constant latitude. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.