zone time


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zone time

[′zōn ′tīm]
(astronomy)
The local mean time of a reference or zone meridian whose time is kept throughout a designated zone; the zone meridian is usually the nearest meridian whose longitude is exactly divisible by 15°.

Zone Time

 

a system for reckoning time, based on the division of the earth’s surface into 24 time zones. All points within a single zone have the same zone time at every moment, while the zone time of adjacent zones will differ by precisely one hour. In the system of zone time, 24 meridians separated by 15° of longitude are taken as the mean meridians of the time zones. Boundaries of the zones passing over oceans and seas, as well as over sparsely populated regions, are represented by meridians 7.5° east and west of the mean meridian. For greatest convenience, boundaries in other regions of the earth coincide with state and administrative boundaries, railroads, rivers, mountain ranges, and other natural boundaries close to the mean meridians.

By international agreement, the meridian with longitude 0° (Greenwich meridian) is taken as the initial meridian. The time zone corresponding to it is the zero zone, and its time is referred to as universal time. The other zones are assigned the numbers one through 23, going from the zero zone to the east. The difference between the zone time of a certain time zone and universal time is equal to the number of the zone.

The times of certain zones have acquired special names. For example, zero zone time is referred to as Western European time; first zone time, as Central European time; and second zone time, as Eastern European time (outside the Soviet Union). The Soviet Union is covered by the second through 12th time zones, inclusively.

Clocks are advanced one or more hours during the summer in many countries (daylight saving time) in order to use natural light in the most efficient manner and to conserve electrical energy. In 1930, standard time in the USSR was advanced one hour beyond zone time. As a result, all points within a given zone utilize the time of the zone to the east of their zone. Standard time in the second time zone, within which Moscow is located, is called Moscow time.

In spite of the convenience of zone time, a number of countries do not use the times of their time zones. Instead, they use over their entire territory either the local time of the capital or a time near that of the capital. The astronomical annual Nautical Almanac (Great Britain) has provided descriptions of the boundaries of time zones every year since 1941 and the accepted manner of reckoning time wherever zone time is not employed as well as all subsequent changes that have been made in time systems.

Before the introduction of zone time, most countries used civil time, which differs for every two points with different longitudes. The inconveniences associated with this system became particularly acute with the development of railroads and telegraph communications. During the 19th century, a number of countries introduced their own standard time, most often the civil time of the capital. This system, however, was not suited to countries with vast stretches of land encompassing many degrees of longitude, since the accepted way of reckoning time would significantly differ from the civil time in distant reaches of the country. In some countries, standard time was introduced only for use on railroads and with the telegraph. The civil time of the Pulkovo Observatory, referred to as St. Petersburg time, was used for this purpose in Russia.

Zone time was proposed by the Canadian engineer S. Fleming in 1878 and first in introduced in the USA in 1883. In 1884 an agreement was signed at an international conference of 26 nations in Washington, D. C, although the transition to this system of reckoning time took many years. Zone time was introduced in the Soviet Union on July 1, 1919, after the Great October Socialist Revolution.

REFERENCES

Kulikov, K. A. Kurs sfericheskoi astronomii, 2nd ed. Moscow, 1969.

zone time

zone time
Zone time.
The local time in a given zone. The earth is arbitrarily divided into 24 zones, each 15° wide. The standard meridians of the zones are removed from Greenwich by multiples of 15°, with the extremities of all zones bounded by 7.5° east and west of the standard (central) meridian. Each zone keeps the local mean time (LMT) of its standard (central) meridian. The LMT of each zone differs from GMT (Greenwich mean time) by one hour, or multiples of one hour. The Greenwich meridian is the reference or starting point for the zones. The GMT is kept in zone 0 (i.e., 7.5° W to 7.5° E). The zones are numbered 1 through 12 east and west of Greenwich. The easterly zones are negative and the westerly zones positive; the zone numbers are the correction in the hours to be applied to the zone time to obtain the GMT. Zone time + Zone number = GMT, or Zone time = GMT − Zone number. Many zone boundary locations differ from the above for political and economic reasons.
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