Constructing an SF Universe
   Excellent article by professional, published science fiction author, S. Andrew Swann.
   http://www.sff.net/people/SASwann/text/wb.htm

Planetary Fact Sheets
   Extensive physical data describing the planets, satellites, and comets of our solar system, courtesy of NASA's National Space Science Data Center. Potentially useful to designers of science fiction settings and the detail-minded.
   http://nssdc.gsfc.nasa.gov/planetary/planetfact.html