Fitzpatrick, Richard (2. 2. 2006). „Planetary orbits”. Classical Mechanics – an introductory course. The University of Texas at Austin. Архивирано из оригинала 3. 3. 2001. г.
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Fitzpatrick, Richard (2. 2. 2006). „Planetary orbits”. Classical Mechanics – an introductory course. The University of Texas at Austin. Архивирано из оригинала 3. 3. 2001. г.