A sphere is a perfectly round three dimensional shape similar to a round ball you might play soccer or basketball with.

All points on the surface of a sphere are the same distance from the center.

A sphere is perfectly symmetrical around its center.

The distance from the center of a sphere to its surface is called the radius.

The maximum distance through the sphere is called the diameter, it is twice the size of the radius.

The value of Pi (π) to 2 decimal places is 3.14, it comes in handy when working out the volume and surface area of a sphere.

To find the volume of a sphere you can use the following formula:  Volume = 4/3 π r³
In an easier to read form: Volume = 4/3 * Pi * r * r * r

To find the surface area of a sphere you can use the following formula: Area = 4 π r²
In an easier to read form: Area = 4 * Pi * r * r

Sometimes a sphere is given a north and south pole (found on opposite sides of the surface).

An equator is a circle that is the same distance from the north and south poles.

A sphere can be divided into two equal hemispheres by a flat two dimensional surface (plane) that passes through the center.

The words north pole, south pole, equator and hemispheres are often used when talking about planet Earth even though it isn’t really a sphere, it’s more like a flattened sphere (oblate spheroid).