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longitude

(Encyclopedia)longitude ln´jtood [key], angular distance on the earth's surface measured along any latitude line such as the equator east or west of the prime meridian. A meridian of longitude is an imagin...

international date line

(Encyclopedia)international date line, imaginary line on the earth's surface, generally following the 180° meridian of longitude, where, by international agreement, travelers change dates. Traveling eastward acros...

prime meridian

(Encyclopedia)prime meridian, meridian that is designated zero degree (0°) longitude, from which all other longitudes are measured. By international convention, it passes through the site of the Royal Observatory ...

occultation

(Encyclopedia)occultation klt´shn [key], in astronomy, eclipse of one celestial body by another, e.g., when the moon lies between a star and the earth. Occultations of stars by the moon are important in ...

chronometer

(Encyclopedia)chronometer krnm´tr [key], instrument for keeping highly accurate time, used especially in navigation. Before the advent of radio time signals it was the only device that provided the time ac...

Maskelyne, Nevil

(Encyclopedia)Maskelyne, Nevil ms´kln [key], 1732–1811, English astronomer. Maskelyne received his education at Westminster School and Trinity College, Cambridge. Appointed astronomer royal at the Royal Ob...

Mayer, Johann Tobias

(Encyclopedia)Mayer, Johann Tobias y´hän tb´äs m´r [key], 1723–62, German mathematician and astronomer. In 1751 he became professor of economics and mathematics at the Univ. of Göttingen, and in 1...

civil time

(Encyclopedia)civil time, local time based on universal time. Civil time may be formally defined as mean solar time plus 12 hr; the civil day begins at midnight, while the mean solar day begins at noon. Civil time ...

galactic coordinate system

(Encyclopedia)galactic coordinate system, astronomical coordinate system in which the principal axis is the galactic equator (the intersection of the plane of the Milky Way with the celestial sphere) and the refere...

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