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Eudoxus of Cnidus

(Encyclopedia)Eudoxus of Cnidus yo͞odŏkˈsəs, nīˈdəs [key], 408?–355? b.c., Greek astronomer, mathematician, and physician. From the accounts of various ancient writers, he appears to have studied with Plat...

Harvard College Observatory

(Encyclopedia)Harvard College Observatory, astronomical observatory located in Cambridge, Mass., operated by Harvard (Harvard College at the time of the observatory's founding in 1839). Its equipment includes a 61-...

Greenwich mean time

(Encyclopedia)Greenwich mean time or Greenwich meridian time (GMT), the former name for mean solar time at the site of the Royal Observatory in Greenwich, England, which is located on the prime meridian. In 1925 th...

Pegasus, in astronomy

(Encyclopedia)Pegasus pĕgˈəsəs [key], in astronomy, northern constellation lying SW of Andromeda and SE of Cygnus. It is named for the mythological winged horse Pegasus. The constellation is easily recognized b...

McDonald Observatory

(Encyclopedia)McDonald Observatory, astronomical observatory located on Mt. Locke, near Fort Davis, Tex.; founded in 1932, sponsored by the Univ. of Texas in cooperation with the Univ. of Chicago. Its equipment inc...

Kirchhoff, Gustav Robert

(Encyclopedia)Kirchhoff, Gustav Robert go͝osˈtäf rōˈbĕrt kĭrkhˈhôf [key], 1824–87, German physicist. He served as professor of physics at the universities of Breslau (1850–54), Heidelberg (1854–74), ...

International Geophysical Year

(Encyclopedia)International Geophysical Year (IGY), 18-month period from July, 1957, through Dec., 1958, during a period of maximum sunspot activity, designated for cooperative study of the solar-terrestrial enviro...

retrograde motion

(Encyclopedia)retrograde motion, in astronomy, real or apparent movement of a planet, dwarf planet, moon, asteroid, or comet from east to west relative to the fixed stars. The most common direction of motion in the...

planet

(Encyclopedia)planet [Gr.,=wanderer], a large nonluminous body of rock, gas, or ice that orbits the sun or another star, has a rounded shape due to gravity, and has cleared its orbit of smaller objects. The term, o...

ephemeris time

(Encyclopedia)ephemeris time (ET), astronomical time defined by the orbital motions of the earth, moon, and planets. The earth does not rotate with uniform speed, so the solar day is an imprecise unit of time. Ephe...