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eposcorr (eposcorr-3.9.2) [xmmsas_20050815_1803-6.5.0]

The errors in the Description Parameters Home Index

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Some spherical geometry

eposcorr calculates angular distances directly using spherical trigonimetry. In particular the following is used to calculate the angular distance, $\theta$, between two sources (labeled 1 and 2).
\begin{displaymath} \cos( \theta) = \sin(\delta_1) \sin(\delta_2) + \cos(\delta_1) \cos(\delta_2) cos(\Delta\alpha), \end{displaymath} (9)

where $\delta$ refers to the declination of a source and $\Delta\alpha =\alpha_1 - \alpha_2$, the difference of the right ascension of the two sources.


XMM-Newton SOC/SSC -- 2005-08-15