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| Astrophysics Data System | NASA/Harvard University. Search over 4 million bibliographic records, some with full text. |
| CRC Handbook of Physics and Chemistry | |
| Encyclopedia Astronautica | Mark Wade. Information on U.S., Soviet/Russian, Chinese, Japanese, and European astronautics. |
| Encyclopedia Britannica | Online Version. |
| Extrasolar Planets Encyclopedia | Jean Schneider, Observatoire de Paris. |
| Journey Through the Galaxy | Stuart Robbins, Case Western Reserve. Essays, glossary, links, news. |
| Physics and Astronomy Reference | Calculators, constants, equations, links , news, etc. |
| SIMBAD Astronomical Database | Harvard University. Centre de Donnees Astronomiques de Strasbourg. Information and bibliographic references on >3 million objects. Search by name or location. | |