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solar constant

(Encyclopedia)solar constant, the average amount of radiant energy received by the earth's atmosphere from the sun; its value is about 2 calories per min incident on each square centimeter of the upper atmosphere. ...

phase, in astronomy

(Encyclopedia)CE5 Phases of the moon phase, in astronomy, the measure of how much of the illuminated surface of a planet or satellite can be seen from a point at a distance from that body; the term is most ofte...

space station

(Encyclopedia)space station or space platform, artificial earth satellite, usually manned, that is placed in a fixed orbit and can serve as a base for astronomical observations; zero-gravity materials processing; s...

Kepler's laws

(Encyclopedia)CE5 Schematic representation of Kepler's second law: The areas ABF and A′B′F′ are equal and are swept out in equal intervals of time by a planet orbiting around the sun (at F). Kepler's laws...

Kirkwood gaps

(Encyclopedia)Kirkwood gaps, regions in the asteroid belt within which few asteroids are found. Astronomer Daniel Kirkwood first observed (1886) that few asteroids had an orbital period close to 1⁄2, 1⁄3, or 2�...

binary star

(Encyclopedia)CE5 A. Eclipsing binary: Primary component passing behind secondary (dimmer) component B. Light curve for eclipsing binary binary star or binary system, pair of stars that are held together by the...

Venus, in astronomy

(Encyclopedia)Venus, in astronomy, 2d planet from the sun; it is often called the evening star or morning star and is brighter than any object in the sky except the sun and the moon. Because its orbit lies between ...

space probe

(Encyclopedia)space probe, space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is...

sidereal year

(Encyclopedia)sidereal year, time required for the earth to complete an orbit of the sun relative to the stars. The sidereal year is 365 days, 6 hr, 9 min, 9.5 sec of mean solar time (see solar time). It is 20 min ...

Pallas, in astronomy

(Encyclopedia)Pallas pălˈəs [key], in astronomy, 2d asteroid to be discovered. It was found in 1802 by H. Olbers. The second largest asteroid, it has a diameter of c.300 mi (480 km). Its orbit has a semimajor ax...