We use a best of approach with images, selecting a key set of images that best tell the story of the planet, celestial object or spacecraft. Comprehensive planetary image libraries can be found at http://photojournal.jpl.nasa.gov/ and http://hubblesite.org/gallery/. Many missions and observatories also have excellent and unique image collections.

These are the primary sources for information in this section:

Jet Propulsion Laboratory Solar System Dynamics

• Main Page: http://ssd.jpl.nasa.gov/
• Astrodynamic Constants: http://ssd.jpl.nasa.gov/?constants
• Planets and Pluto: Physical Characteristics: http://ssd.jpl.nasa.gov/?planet_phys_par
• Keplerian Elements for Approximate Positions of the Major Planets: http://ssd.jpl.nasa.gov/txt/p_elem_t1.txt
• Planetary Satellite Discovery Circumstances: http://ssd.jpl.nasa.gov/?sat_discovery
• Planetary Satellite Physical Parameters: http://ssd.jpl.nasa.gov/?sat_phys_par
• Planetary Satellite Mean Orbital Parameters: http://ssd.jpl.nasa.gov/?sat_elem
• Small-Body Database Browser: http://ssd.jpl.nasa.gov/sbdb.cgi#top
• Meteor Streams: http://ssd.jpl.nasa.gov/?meteor_streams

Goddard Space Flight Center National Space Science Data Center

• Planetary Fact Sheet - Metric: http://nssdc.gsfc.nasa.gov/planetary/factsheet/
• Planetary Fact Sheet - U.S. Units: http://nssdc.gsfc.nasa.gov/planetary/factsheet/planet_table_british.html
• Planetary Fact Sheet - Ratio to Earth Values: http://nssdc.gsfc.nasa.gov/planetary/factsheet/planet_table_ratio.html
• Master Catalog - Spacecraft Query: http://nssdc.gsfc.nasa.gov/nmc/SpacecraftQuery.jsp

International Astronomical Union

• Astronomical Constants : Current Best Estimates: http://maia.usno.navy.mil/NSFA/NSFA_cbe.html
• Ring and Ring Gap Nomenclature: http://planetarynames.wr.usgs.gov/Page/Rings
• Small Body Nomenclature: http://www.ss.astro.umd.edu/IAU/csbn/
• Naming of Astronomical Objects: http://www.iau.org/public/themes/naming/
• Gazetteer of Planetary Nomenclature: http://planetarynames.wr.usgs.gov/
• Planet and Satellite Names and Discoverers: http://planetarynames.wr.usgs.gov/Page/Planets
• Objects Cross-listed Both as Comet and Minor Planet: http://www.ss.astro.umd.edu/IAU/csbn/crosslist.shtml
• International Astronomical Union Minor Planet Center: http://minorplanetcenter.net/
• Minor Planet Center: http://minorplanetcenter.org/iau/mpc.html
• New- And Old-Style Minor Planet Designations: http://www.minorplanetcenter.net/iau/info/OldDesDoc.html
• Minor Planet Center Index: http://www.minorplanetcenter.net/iau/TheIndex.html
• Discovery Circumstances: Numbered Minor Planets: http://www.minorplanetcenter.net/iau/lists/NumberedMPs.html
• Minor Planet Names: Alphabetical List: http://www.minorplanetcenter.net/iau/lists/MPNames.html
• The Distant Artificial Satellites Observation Page: http://www.minorplanetcenter.net/iau/SpaceJunk/SpaceJunk.html

Universities

• Scott S. Sheppard's Satellite and Moon Page: Jupiter, Saturn, Uranus, Neptune and Pluto: http://home.dtm.ciw.edu/users/sheppard/satellites/
• Scott S. Sheppard's Jupiter's Known Satellites Page: http://home.dtm.ciw.edu/users/sheppard/satellites/jupsatdata.html
• Scott S. Sheppard's Saturn's Known Satellites Page: http://www.dtm.ciw.edu/users/sheppard/satellites/satsatdata.html
• Scott S. Sheppard's Uranus' Known Satellites Page: http://www.dtm.ciw.edu/users/sheppard/satellites/urasatdata.html
• Scott S. Sheppard's Neptune's Known Satellites Page: http://www.dtm.ciw.edu/users/sheppard/satellites/nepsatdata.html
• Scott S. Sheppard's Pluto's Known Satellites Page: http://home.dtm.ciw.edu/users/sheppard/satellites/plutosatdata.html

Other Sources

• NASA Technical Reports Server: http://ntrs.nasa.gov
• Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000: http://ntrs.nasa.gov/search.jsp?R=20020052429
• International Meteor Organization: http://www.imo.net/
• Gary W. Kronk's Cometography : http://cometography.com/periodic_comets.html