Parallaxes and Eclipses

  • Olaf Pedersen
Part of the Sources and Studies in the History of Mathematics and Physical Sciences book series (SHMP)


The theories of the Sun and Moon developed in the preceding chapters have the feature in common that they provide exactly geocentric co-ordinates. In other words they presuppose an ideal observer situated at the centre T of the Earth and observing the centre of the planet in the direction TP (see Figure 7.1). A real observer placed at the point A on the surface of the Earth will see P in the direction AP. Unless P is at the zenith of A, the lines of vision TP and AP will include an angle called the parallax of P (in modern terms the daily parallax). It is the difference between the observed and the geocentric zenith distances of P. If we want to know the actual position of P (the direction of AP) then it is necessary to adjust the geocentric position derived from theory with a certain correction for parallax.


Solar Eclipse Lunar Eclipse Zenith Distance Apparent Diameter Lunar Theory 
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Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • Olaf Pedersen
    • 1
  1. 1.History of Science DepartmentUniversity of AarhusAarhusDenmark

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