Information on this site is gathered either directly from scientists and engineers working on active missions or from Websites from global space agencies, including NASA and the European Space Agency. We also rely on information provided by research and development centers, national and international observatories, private observatories and others on the list below.

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 on this site:

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