A unified body or collection of knowledge regarding a specific subject.

(astronomy) An abstract sphere of infinite radius which serves as the imaginary backdrop for celestial objects, and of which the visible sky is one hemisphere.

A hypothetical system of orbiting solar power satellites meant to completely encompass a star and capture its entire energy output. / (science fiction) A solid shell of matter enclosing a star.

An instrument consisting of graduated metal circles used to represent the motions of celestial bodies around the earth.

(topology) A manifold whose homology is the same as that of some sphere of the same dimension

plural of homology sphere

plural of Dyson sphere

(cosmology) In geocentric cosmologies, that region of the cosmos from the centre of the Earth to the moon, believed to comprise the four classical elements (earth, air, fire and water) and to be subject to generation and corruption.

plural of sphere of influence

A manifold (of any dimension) homeomorphic to a sphere but not diffeomorphic to the standard sphere.