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day

(Encyclopedia)day, period of time for the earth to rotate once on its axis. The ordinary day, or solar day, is measured relative to the sun, being the time between successive passages of the sun over a stationary o...

sunburn

(Encyclopedia)sunburn, inflammation of the skin caused by actinic rays from the sun or artificial sources. Moderate exposure to ultraviolet radiation is followed by a red blush, but severe exposure may result in bl...

solar energy

(Encyclopedia)solar energy, any form of energy radiated by the sun, including light, radio waves, and X rays, although the term usually refers to the visible light of the sun. Solar energy is needed by green plants...

comet

(Encyclopedia)CE5 Comet: Whatever the direction of a comet's flight, its “tail” always points away from the sun. The tail disappears when the comet is far from the sun. comet [Gr.,=longhaired], a small cele...

Menzel, Donald Howard

(Encyclopedia)Menzel, Donald Howard, 1901–76, American astrophysicist, b. Florence, Colo. From 1926 to 1932 he was with the Lick Observatory in Calif. In 1932 he joined the faculty at Harvard, where he became pro...

quadrature

(Encyclopedia)quadrature, in astronomy, arrangement of two celestial bodies at right angles to each other as viewed from a reference point. If the reference point is the earth and the sun is one of the bodies, a pl...

Scholz's star

(Encyclopedia)Scholz's star, dim binary star system, consisting of a red dwarf and brown dwarf, in the constellation Monoceros, apparent magnitude 18.3. The red dwarf is a tiny star, with less than ten percent the ...

Mercury, in astronomy

(Encyclopedia)Mercury, in astronomy, nearest planet to the sun, at a mean distance of 36 million mi (58 million km); its period of revolution is 88 days. Mercury passes through phases similar to those of the moon a...

precession of the equinoxes

(Encyclopedia)CE5 Precession of the equinoxes (the points at which the earth's celestial equator intersects its ecliptic) is due to the slow rotation of the earth's axis around a perpendicular to the ecliptic. ...

Marquis, Don

(Encyclopedia)Marquis, Don (Donald Robert Perry Marquis) märˈkwĭs [key], 1878–1937, American author, b. Walnut, Ill. In 1912 he began the humorous column “The Sun Dial” in the New York Sun and later conduc...