Why Halley Did Not Discover Proper Motion and Why Cassini Did

  title={Why Halley Did Not Discover Proper Motion and Why Cassini Did},
  author={Frank Verbunt and M. V. van der Sluys},
  journal={Journal for the History of Astronomy},
  pages={383 - 397}
In 1717, Halley compared contemporaneous measurements of the latitudes of four stars with earlier measurements by ancient Greek astronomers and by Brahe, and from the differences concluded that these four stars showed proper motion. An analysis with modern methods shows that the data used by Halley do not contain significant evidence for proper motion. What Halley found are the measurement errors of Ptolemaios and Brahe. Halley further argued that the occultation of Aldebaran by the Moon on 11… 
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