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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...

universal gas constant

(Encyclopedia)universal gas constant: see gas laws. ...

Universal Postal Union

(Encyclopedia)Universal Postal Union (UPU), specialized agency of the United Nations since 1948, with headquarters at Bern, Switzerland. Established in 1875 following adoption of the Universal Postal Convention, it...

Universal Product Code

(Encyclopedia)Universal Product Code: see barcode. ...

local solar time

(Encyclopedia)local solar time: see solar time. ...

mean solar time

(Encyclopedia)mean solar time: see solar time. ...

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...

equation of time

(Encyclopedia)equation of time: see solar time. ...

apparent solar time

(Encyclopedia)apparent solar time: see solar time. ...

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...