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time zone

(Encyclopedia)time zone: see standard time.

space-time

(Encyclopedia)space-time, central concept in the theory of relativity that replaces the earlier concepts of space and time as separate absolute entities. In relativity one cannot uniquely distinguish space and time...

Orbiting Solar Observatory

(Encyclopedia)Orbiting Solar Observatory (OSO), series of eight orbiting observatories (see observatory, orbiting) launched between 1962 and 1971 by the National Aeronautics and Space Administration (NASA) to study...

equal-time rule

(Encyclopedia)equal-time rule, a Federal Communications Commission rule that requires equal air time for all major candidates competing for political office. It was preceded by the fairness doctrine, abolished in 1...

daylight saving time

(Encyclopedia)daylight saving time (DST), time observed when clocks and other timepieces are set ahead so that the sun will rise and set later in the day as measured by civil time. The amount of daylight on a given...

time , in music

(Encyclopedia)time, in music: see tempo; meter; rhythm; syncopation; metronome and musical notation. ...

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...

year

(Encyclopedia)year, time required for the earth to complete one orbit about the sun. The solar or tropical year is measured relative to the sun and is equal to 365 days, 5 hr, 48 min, 46 sec of mean solar time (see...

tropical year

(Encyclopedia)tropical year, time between successive vernal equinoxes; 365 days, 5 hr, 48 min, 46 sec of mean solar time (see solar time). The tropical year is the basis of the year used in the Gregorian calendar. ...

Kitt Peak National Observatory

(Encyclopedia)Kitt Peak National Observatory, astronomical observatory located southwest of Tucson, Ariz.; it was founded in 1958 under contract with the National Science Foundation and is administered by the Assoc...