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
Includes 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
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