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TY - CHAP AU - Pedersen, Olaf A2 - Pedersen, Olaf ED - Jones, Alexander PY - 2011 DA - 2011// TI - Parallaxes and Eclipses BT - A Survey of the Almagest: With Annotation and New Commentary by Alexander Jones SP - 203 EP - 235 PB - Springer New York CY - New York, NY AB - 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. SN - 978-0-387-84826-6 UR - https://doi.org/10.1007/978-0-387-84826-6\_7 DO - 10.1007/978-0-387-84826-6_7 ID - Pedersen2011 ER -