\begin{definition}[Definition:Colatitude (Terrestrial)]
Let $J$ be a point on Earth's surface that is not one of the two poles $N$ and $S$.
Let $\phi$ denote the latitude of $J$.
The '''colatitude''' of $J$ is the (spherical) angle $90 \degrees - \phi$, that is:
:if $J$ is in the northern hemisphere of Earth, the '''colatitude''' is the (spherical) angle $\sphericalangle NOJ$
:if $J$ is in the southern hemisphere of Earth, the '''colatitude''' is the (spherical) angle $\sphericalangle SOJ$.
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\end{definition}