Re-establishing Kepler's first two laws for planets in a concise way through the non-stationary Earth

W. Y. Hsiang, H. C. Chang, Herng Yao, P. S. Lee

Research output: Contribution to journalArticle


In this we design a simple and insightful way to achieve Kepler's first two laws for planets. The approach is quite different from what we have done for the Earth before. It is because the planet-Sun distance can be determined only through the Earth-Sun distance in the analysis. By applying the law of equal areas for the Earth and the observed angular speeds of a planet over the Sun, the law of equal areas for planets can be re-constructed. Furthermore, for the periodicity of a planet to the Sun, the distance from each planet to the Sun may be expressed as an angular periodic function. By coordinating with the observed data, this periodic distance function depicts an exact elliptical path. Here, we apply relatively easy mathematical skills to illustrate the invariant forms of planetary motions and indicate the key factors used to analyse the motions in complicated planetary systems.

Original languageEnglish
Article number045006
JournalEuropean Journal of Physics
Issue number4
Publication statusPublished - 2015 Jul 1



  • Kepler
  • law of ellipses
  • law of equal areas
  • planet

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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