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RT @FrontAstroSpace: Proper Motion and Secular Variations of Keplerian Orbital Elements: Alexey G. Butkevich https://t.co/ozX5Jh3v67
RT @FrontAstroSpace: Proper Motion and Secular Variations of Keplerian Orbital Elements: Alexey G. Butkevich https://t.co/ozX5Jh3v67
Proper Motion and Secular Variations of Keplerian Orbital Elements: Alexey G. Butkevich https://t.co/ozX5Jh3v67