Any plane that passes through the centre of a
sphere divides the sphere into two hemispheres.
Formula
The formula to calculate the total area [latex]A[/latex] of a hemisphere of radius [latex]r[/latex] is:
[latex]A=\pi r^{2}+\frac{4\pi r^{2}}{2}=3\pi r^{2}[/latex].
Geographic note
In geography, a hemisphere is one half of the Earth. The globe can be divided into two hemispheres,
north and
south, each of which is centred at a point called a
pole and separated from the other by a
great circle.
Similarly, the Earth can be divided into the
Eastern Hemisphere and the
Western Hemisphere, which are east and west of the Greenwich meridian.
