Williams, Darren M. (November 2003). "Average distance between a star and planet in an eccentric orbit". American Journal of Physics. 71 (11): 1198–1200. Bibcode:2003AmJPh..71.1198W. doi:10.1119/1.1578073.
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Williams, Darren M. (November 2003). "Average distance between a star and planet in an eccentric orbit". American Journal of Physics. 71 (11): 1198–1200. Bibcode:2003AmJPh..71.1198W. doi:10.1119/1.1578073.