CenterThe point at the middle of the sphere. Every point on the surface is the same distance from it.
RadiusA line from the center to the surface. Its length is also called the radius.
DiameterA line across the sphere through its center. It is twice as long as the radius.
SurfaceThe curved outside of the sphere. It has no edges and no corners.
PoleOne of two opposite points on the surface. A line through the center, the axis, meets the sphere at its two poles.
Circles, half and cap 4
Great circleA circle on the sphere that shares its center. It divides the sphere into two equal halves.
HemisphereHalf of a sphere. A great circle divides the sphere into two hemispheres.
Small circleA circle on the sphere whose plane misses the center. It is smaller than a great circle.
Spherical capThe part of a sphere cut off by a flat plane. The small circle is its edge here.
How this list was compiled: Read 2026-10-01. (1) Wikipedia, Sphere, https://en.wikipedia.org/wiki/Sphere : the center and the radius; a radius carried on through the center to the far side makes a diameter, twice the radius; a great circle shares the sphere's center and radius and divides it into two equal hemispheres; a line through the center is an axis and meets the sphere at two poles; circles cut by a plane through the center are great circles and the others are small circles; the spherical cap is in its list of regions. (2) Wolfram MathWorld: Sphere, https://mathworld.wolfram.com/Sphere.html (radius, center, twice the radius is the diameter); Great Circle, https://mathworld.wolfram.com/GreatCircle.html (a section of a sphere containing a diameter; sections that do not are small circles); Small Circle, https://mathworld.wolfram.com/SmallCircle.html ; Hemisphere, https://mathworld.wolfram.com/Hemisphere.html (half a sphere, cut by a plane through its center); Spherical Cap, https://mathworld.wolfram.com/SphericalCap.html (the region of a sphere above or below a plane); Antipodal Points, https://mathworld.wolfram.com/AntipodalPoints.html (the poles of a sphere). (3) Math is Fun, Sphere, https://www.mathsisfun.com/geometry/sphere.html : every point on the surface is the same distance from the center; no edges or vertices; one surface; a hemisphere is exactly half a sphere. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
Label the parts of a sphere on two drawings. The first has the center, a radius, a diameter, the surface and the poles. The second has the circles: a great circle, the hemisphere below it, a small circle and its cap.
Read the full guide
Center, radius and diameter
Every point on the surface is the same distance from the center. A radius runs from the center to the surface; a diameter runs right across through the center and is twice as long.
Great circles and small circles
Slice a sphere with a flat cut. If the cut goes through the center, its edge is a great circle and each piece is a hemisphere. If it misses the center, the edge is a small circle and the smaller piece is a spherical cap.
On a globe the equator is a great circle. The other lines of latitude are small circles.
Questions and answers
What are the main parts of a sphere?
The center, the radius, the diameter and the surface. A sphere has no edges, corners or flat faces, so every other named part is a line, a circle or a region marked on it.
What is a great circle of a sphere?
A circle on the sphere that shares the sphere's center and radius. It divides the sphere into two equal hemispheres.
How is a sphere different from a circle?
A circle is flat; a sphere is a solid shape in three dimensions. Both have a center, a radius and a diameter, but only a sphere has a surface, hemispheres and great circles.