Hemisphere
A sphere is divided into two equal "hemispheres" by any plane that passes through its center. If two intersecting planes pass through its center, then they will subdivide the sphere into four lunes or biangles, the vertices of which all coincide with the antipodal points lying on the line of intersection of the planes.
The antipodal quotient of the sphere is the surface called the real projective plane, which can also be thought of as the northern hemisphere with antipodal points of the equator identified.
The round hemisphere is conjectured to be the optimal (least area) filling of the Riemannian circle.
If the planes don't pass through the sphere's center, then the intersection is called spheric section.
Read more about this topic: Sphere
Famous quotes containing the word hemisphere:
“Rome, the city of visible history, where the past of a whole hemisphere seems moving in funeral procession with strange ancestral images and trophies gathered from afar.”
—George Eliot [Mary Ann (or Marian)