This is the Web Edition of "A Trip Into Space", a Coimbra-based electronic book on space science. Both the texts and the photos are by courtesy of National Aeronautics and Space Administration.

Uranus
In True And False Color

These two pictures of Uranus - one in true color (left) and the other in false color - were compiled from images returned on January 17, 1986, by the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million kilometers (5.7 million miles) from the planet, seven days before its closest approach.

The picture on the left has been processed to show Uranus as human eyes would see it from the vantage point of the spacecraft. The picture is a composite of images taken through blue, green, and orange filters. The blue-green color results from the absorption of red light by methane gas in Uranus' deep, cold, and remarkably clear atmosphere. The darker shadings at the upper right of the disk correspond to the day-night boundary on the planet. Beyond this boundary lies the hidden northern hemisphere of Uranus that remains in total darkness as the planet rotates.

The picture on the right uses false colors and contrast enhancement to bring out subtle details in the polar region of Uranus. Images obtained through ultraviolet, violet, and orange filters were respectively converted to blue, green, and red colors to produce the picture. The very slight contrasts visible in true color thus are greatly exaggerated here. In this false-color picture, Uranus reveals a dark polar hood surrounded by a series of progressively lighter concentric bands. One possible explanation is that a brownish haze or smog, concentrated over the pole, is arranged into bands by zonal motions of the upper atmosphere.

Several artifacts of the optics and processing are visible. The occasional doughnut shapes are shadows cast by dust in the camera's optics; the processing necessary to bring out the faint features also brings out these camera blemishes. In addition, the bright pink strip at the lower edge of the planet's limb is an artifact of the image enhancement. In fact, the limb is dark and uniform in color.

The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

Last Update: 2005-Nov-29