\begin{definition}[Definition:Latitude (Terrestrial)]
Let $J$ be a point on Earth's surface that is not one of the two poles $N$ and $S$.
Let $\bigcirc NJS$ be a meridian passing through $J$, whose endpoints are by definition $N$ and $S$.
Let $\bigcirc NJS$ pass through the equator at $L$.
The '''latitude''' of $J$ is the (spherical) angle $\sphericalangle LOJ$ , where $O$ is the center of Earth.
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If $J$ is in the northern hemisphere of Earth, the '''latitude''' is defined as '''latitude $n \degrees$ north''', where $n \degrees$ denotes $n$ degrees (of arc), written $n \degrees \, \mathrm N$.
If $J$ is in the southern hemisphere of Earth, the '''latitude''' is defined as '''latitude $n \degrees$ south''', written $n \degrees \, \mathrm S$.
At the North Pole, the '''latitude''' is $90 \degrees \, \mathrm N$.
At the South Pole, the '''latitude''' is $90 \degrees \, \mathrm S$.
\end{definition}