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: The sun, moon, stars, and planets appear to be placed on the celestial sphere.
2. The imaginary shell formed by the sky: The celestial sphere is 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.