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| any of various groups of stars to which definite names have been given and the section of the heavens occupied by such a group, such as Ursa Major, Andromeda |
| the figure of the moon in its first or last quarter, resembling a segment of a ring tapering to points at the ends |
| Oort cloud (ôrt) Pronunciation Key
A sphere-shaped mass of more than 100 billion comets that makes up the outer edge of the solar system, surrounding the Kuiper belt and the planets. Some comets from this area are drawn into the inner solar system by passing stars and other forces and take more than 200 years to make one complete orbit of the Sun. Compare Kuiper belt. |