One half of a sphere.

Any plane that passes through the centre of a sphere divides the sphere into two hemispheres.

### Formula

The formula to calculate the total area \(A\) of a hemisphere of radius \(r\) is:

\(A=\pi r^{2}+\frac{4\pi r^{2}}{2}=3\pi r^{2}\).

### 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.