(Encyclopedia) time, sequential arrangement of all events, or the interval between two events in such a sequence. The concept of time may be discussed on several different levels: physical,? (Encyclopedia) time, in music: see tempo; meter; rhythm; syncopation; metronome and musical notation. (Encyclopedia) equation of time: see solar time. (Encyclopedia) time zone: see standard 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? (Encyclopedia) standard time, civil time used within a given time zone. The earth is divided into 24 time zones, each of which is about 15 of longitude wide and corresponds to one hour of time.? (Encyclopedia) solar time, time defined by the position of the sun. The solar day is the time it takes for the sun to return to the same meridian in the sky. Local solar time is measured by a sundial? (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? (Encyclopedia) universal time (UT), the international time standard common to every place in the world, it nominally reflects the mean solar time along the earth's prime meridian (renumbered to? (Encyclopedia) sidereal time (ST), time measured relative to the fixed stars; thus, the sidereal day is the period during which the earth completes one rotation on its axis so that some chosen star?