1. An object similar in shape to a ball.
2. In mathematics, a three-dimensional closed surface consisting of all points that are at a given distance from a center.
3. A solid figure bounded by a sphere, or the volume it encloses.
4. A field of knowledge, interest, or activity.
5. An area of control or influence: "The student took no interest in matters beyond her sphere of knowledge."
6. A level or group within a society or a particular social world, stratum of society, or walk of life: "His social sphere was very limited."
7. An astronomical object; such as, a planet, moon, or star.
8. In early astronomical theory, a revolving concentric transparent shell on which the sun, moon, planets, and stars were thought to be fixed as they moved around the earth.
9. The sky, appearing as a hemisphere to an observer; for example, the sphere of the heavens.
10. Etymology: from Greek σφαῖρα, sphaira, "globe, ball" or a perfectly round geometrical object in three-dimensional space; such as, the shape of a round ball.

1. To form into a round shape.
2. To put in or as if in a global zone.
3. To surround or to encompass.

1. The imaginary orbit around the earth on which the sun, moon, stars, and planets appear to be placed.
2. The imaginary shell formed by the sky; usually, represented as an infinite circle, the center of which is the observer's position.

Also known as the "geodesic dome", a dome or structure: A geodesic sphere roughly approximates a hemisphere constructed of many light, straight structural elements in tension, arranged in a framework of triangles to reduce stress and weight.

The natural harmonic tones supposedly produced by the movement of the celestial spheres or the bodies fixed in them.

A theory of Eudoxus from about 400 B.C.; a cosmological theory in which the planets, the sun, and the moon were described as being carried on a series of concentric spheres rotating within one another on different or various axes.

Eudoxus of Cnidus (about 408 B.C. to 347 B.C.) was a Greek astronomer and mathematician.