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eposcorr (eposcorr-3.13) [xmmsas_20190531_1155-18.0.0]


Some spherical geometry

eposcorr calculates angular distances directly using spherical trigonometry. 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 -- 2019-06-02