[Images of Planets (Not graphics)] Courtesy Jet Propulsion Laboratory. Copyright (c) California Institute of Technology, Pasadena, CA. All rights reserved. Based on government-sponsored research under contract NAS7-1260.
Knight, J.D. "Glossary of Astronomy Terms" <http://www.seasky.org/astronomy/sky1a.html> 06-07-00 (08-18-99)