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 across the line, one subtracts one calendar day; traveling westward, one adds a day. The date line is necessary to avoid a confusion that would otherwise result. For example, if an airplane were to travel westward with the sun, 24 hr would elapse as it circled the globe, but it would still be the same day for those in the airplane while it would be one day later for those on the ground below them. The same problem would arise if two travelers journeyed in opposite directions to a point on the opposite side of the earth, 180° of longitude distant. The eastward traveler would set his clock ahead 1 hr for each 15° of longitude (see standard time), so that his clock would gain a total of 12 hr; the westward traveler would set his clock back 1 hr for each 15°, resulting in a total loss of 12 hr. The two clocks would therefore differ by 24 hr, or one calendar day. The apparent paradox is resolved by requiring that the traveler crossing the date line change his date, thus bringing the travelers into agreement when they meet. The international date line does not follow the 180° meridian along its entire course but bends eastward around the eastern tip of Siberia, westward around the Aleutian Islands, and eastward again around various island groups in the South Pacific in order to avoid a time change in populated areas.

date line, international: see international date line.

date, name for a palm (Phoenix dactylifera) and for its edible fruit. Probably native to Arabia and North Africa, it has from earliest times been a principal food in many desert and tropical regions. For some 4,000 years it has been grown near the Tigris and Euphrates rivers. It is cultivated in many other warm regions, including parts of the SW United States and Mexico. The trees sometimes reach a height of 100 ft (30.5 m) and yield fruit for generations. Staminate (male) and pistillate (female) flowers are borne on separate trees, and pollination of those grown commercially is usually done by hand. Seedless dates may be produced without pollination but they are inferior. Heavy, pendant clusters of the sweet, nutritious fruits are produced; the yield after maturity (10 to 15 years) is usually from 100 to 200 lb (45-90 kg) or more per tree annually. Each fruit is 1 to 3 in. (2.54-7.6 cm) long, reddish brown or yellowish brown, and somewhat cylindrical or oblong. When ripe, the bunches of fruit are cut intact from the palm and matured in a warm place. In the Old World, a sugar and a fermented drink are made from the sap of the date palm and other species of Phoenix, and the seeds are sometimes roasted and used as a coffee substitute or pressed for oil, leaving a residue useful for stock feed. The wood of the trunk is often used in construction and the leaves are used for weaving mats and baskets. Dates are classified in the division Magnoliophyta, class Liliopsida, order Arecales, family Palmae.

Tree (Phoenix dactylifera) of the palm family, found in the Canary Islands and northern Africa, the Middle East, Pakistan, India, and California. The trunk, strongly marked with the pruned stubs of old leaf bases, ends in a crown of long, graceful, shining, pinnate leaves. The fruit, called the date, is a usually oblong brown berry. Dates have long been an important food in desert regions, and are the source of syrup, alcohol, vinegar, and a strong liquor. All parts of the tree yield products of economic value, being used variously for timber, furniture, basketry, fuel, rope, and packing material. The seeds are sometimes used as stock feed. The tree is grown as an ornamental along the Mediterranean shores of Europe. Its leaves are used for the celebration of Palm Sunday (among Christians) and the Feast of Tabernacles (among Jews). Date sugar, a product of India, is obtained from the sap of a closely related species, P. sylvestris.

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