World Book Encyclopedia:
copyright 1991 World Book Encyclopedia, Inc.
Voyage Through the Universe (series)
--Time Life Books; Alexandria, Virginia
National Aeronautics and Space Administration
--www.nasa.gov
Space Report
--www.treknet.net/spacereport
The Nine Planets
--http://seds.lpl.arizona.edu/nineplanets/nineplanets/nineplanets.html