Parallaxes and Eclipses (original) (raw)

Abstract

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.

Author information

Authors and Affiliations

  1. History of Science Department, University of Aarhus, Aarhus, 8000, Denmark
    Olaf Pedersen

Authors

  1. Olaf Pedersen
    You can also search for this author inPubMed Google Scholar

Editor information

Editors and Affiliations

  1. Institute for the Study of the, Ancient World, New York University, East 84th Street 15, New York, 10028, New York, USA
    Alexander Jones

Rights and permissions

© 2011 Springer Science+Business Media, LLC

About this chapter

Cite this chapter

Pedersen, O. (2011). Parallaxes and Eclipses. In: Jones, A. (eds) A Survey of the Almagest. Sources and Studies in the History of Mathematics and Physical Sciences. Springer, New York, NY. https://doi.org/10.1007/978-0-387-84826-6\_7

Download citation

Publish with us