Heliogabalus See Elagabalus
heliopause Boundary between the heliosphere—the teardrop-shaped region around the Sun created by the solar wind and filled with solar mag¬ netic fields and outward-moving gas—and the zone of transition to the interstellar medium. Its tail is estimated to reach 50-100 astronomical units from the Sun, encompassing the orbits of all the major planets. Its shape changes, influenced by a wind of interstellar gas produced by the Sun’s motion through it.
Heliopolis \,he-le-'a-p3-bs\ biblical On Ancient holy city, Egypt. The city, which is now mainly ruins lying northeast of Cairo, was the seat of worship of the Egyptian sun god Ra. Its great temple of Ra was second in size only to that of Amon at Thebes, and its priesthood wielded great influence. In the New Kingdom, the temple became the repository of royal records. The city’s surviving monument is the obelisk of Sesostris I, the oldest in existence. Two obelisks erected there by Thutmose III and known as Cleopatra’s Needles now stand on the Thames River embankment in London and in Central Park, New York City.
Helios \'he-le-,os\ Sun god of ancient Greece. He drove his chariot from east to west across the sky each day and sailed across the ocean each night in a huge cup. He was especially worshiped on Rhodes, where he was considered the chief god as early as the 5th century bc. In Greece he was later displaced by Apollo. The Romans worshiped him as Sol.
heliotrope Vhe-le-s-.tropN Any of about 250 species of tropical or tem¬ perate, mostly herbaceous, plants that make up the genus Heliotropium, in the borage family, found through¬ out the world. Included are many weedy species. The best known is garden heliotrope ( H . arborescens ), a shrubby perennial that bears fragrant, purple to white, flat-clustered, five- lobed flowers in coiled sprays, simi¬ lar tO FORGET-ME-NOTS.
helium Chemical element, chemical symbol He, atomic number 2. A noble gas, it is colourless, odourless, taste¬ less, completely unreactive, and non¬ toxic. First found by spectroscopy of the Sun’s atmosphere in 1868, it is the second most abundant and second-lightest element in the uni¬ verse (after hydrogen). Helium makes up a tiny proportion of the atmo¬ sphere but as much as 7% of natural gas. It is the product of radioactive decay (see radioactivity) and is used in helium dating. It is used as an inert gas in welding, rocket propulsion, balloon flight, hyperbaric chambers, deep-sea diving (see nitrogen narcosis), gas chromatography, luminous signs, and cryogenics. Liquid helium, which exists only below -452 °F (-268.9 °C, about 4° C above absolute zero), is a “quantum fluid” (see fluid mechanics; quantum mechanics), with unique properties, including superfluidity, super¬ conductivity, and near-zero viscosity.
helium dating Method of dating that depends on the production of helium during the decay of radioactive isotopes of uranium and thorium.
Because of this decay, the helium content of any mineral or rock capable of retaining helium will increase during the lifetime of that mineral or rock, and the ratio of helium to its radioactive progenitors then becomes a measure of geologic time. Fossils may also be dated by helium dating. The relatively large amount of helium produced in rocks may make it possible to extend helium dating to rocks and minerals as young as a few tens of thousands of years old.
hell Abode of evildoers after death, or the state of existence of souls damned to punishment after death. Most ancient religions included the concept of a place that divided the good from the evil or the living from the dead (e.g., the gloomy subterranean realm of Hades in Greek religion, or the cold and dark underworld of Nilfheim or Hel in Norse mythology). The view that hell is the final dwelling place of the damned after a last judgment is held by Zoroastrianism, Judaism, Christianity, and Islam. The Jewish concept of Gehenna as an infernal region of punishment for the wicked was the basis for the Christian vision of hell as the fiery domain of Satan and his evil angels and a place of punishment for those who die without repenting of their sins. In Hinduism hell is only one stage in the career of the soul as it passes through the phases of reincarnation. The schools of Buddhism have varying conceptions of hell, usually entailing some kind of punishment or purgatory. In Jainism, hell is a purgatory in which sinners are tormented by demons until the evil of their lives has been exhausted.
hellbender Salamander ( Cryptobranchus alleganiensis, family Crypto- branchidae) found in swift-flowing rivers in the eastern and central U.S. It grows to about 25 in. (63 cm) long, has a stout body, flat head, broad tail fin, and wrinkled sides, and is typically brownish gray with black spots. Adults have lungs, but a gill slit persists from the larval stage on each side behind the head. Wrinkled fleshy folds on the body and legs increase surface area for respiration through the skin, the principal mode of oxygen intake. Hellbenders lie under stones during the day, emerging at night to feed on crayfish, small fishes, and worms.
hellebore \ , he-b-,bor\ Member of either of two genera of poisonous herbaceous plants, Helleborus (but¬ tercup family) and Veratrum (uly fam¬ ily). Some are grown as garden ornamentals. Helleborus, consists of about 20 species of perennial plants native to Eurasia; most are nearly stemless, with thick roots and long- stalked, divided leaves and showy flowers. Veratrum contains about 45 species, better called false helle¬ bores, native widely to damp areas of the Northern Hemisphere. They have simple leaves and clusters of small flowers.
Hellenistic Age In the eastern Mediterranean and the Middle East, the period between the death of Alexander the Great (323 bc) and the con¬ quest of Egypt by Rome (30 bc). Alexander and his successors established Greek monarchies that controlled the area from Greece to Afghanistan. The Macedonian Antigonid kingdom, the Middle Eastern Seleucid kingdom, and the Egyptian Ptolemaic kingdom spread Greek culture, mixed Greek and non-Greek populations, and fused Greek and Oriental elements. They pro¬ duced effective bureaucracies and a common, creative culture based at Alexandria. A great flowering of the arts, literature, and science occurred particularly in the period 280-160. The decline of the Hellenic states occurred as Rome gained strength and won wars against Macedonia and against Mithradates VI Eupator, turning the kingdoms and their allies into Roman provinces. Egypt was the last to fall, after having been drawn into the civil war between Mark Antony and Octavian (Augustus).
Heller, Joseph (b. May 1, 1923, Brooklyn, N.Y., U.S.—d. Dec. 12, 1999, East Hampton, N.Y.) U.S. writer. Heller flew 60 combat missions as a bombardier in World War II before finishing his studies at Columbia and Oxford and working as an advertising copywriter. His satirical novel Catch-22 (1961), based on his wartime experiences, was one of the most significant works of postwar protest literature and a huge critical and popular success. His later novels include Something Happened (1974), Good as Gold (1979), God Knows (1984), and Closing Time (1994).
Garden heliotrope (Heliotropium arborescens)
WALTER DAWN
Green hellebore (Helleborus viridis)
G.E. HYDE-THE NATURAL HISTORY PHOTOGRAPHIC AGENCY/EB INC.
© 2006 Encyclopaedia Britannica, Inc.
Heller ► Hemacandra I 859
Heller, Yom Tov (Lipmann ben Nathan Ha-Levi) (b. 1579, Wallerstein, Bavaria—d. Sept. 7, 1654, Krakow, Pol.) Bohemian Jewish religious scholar. After serving as rabbi in Moravia and Vienna, he became chief rabbi in Prague in 1627. He was forced to collect a heavy tax imposed on Jews by Ferdinand II during the Thirty Years’ War, damaging his reputation in the Jewish community. Later, as rabbi in Volhynia, he earned the enmity of wealthy Jews for denouncing simony. From 1643 he was chief rabbi in Krakow. He is best known for his commentary on the Mishna, The Additions of Yom Tov (1614-17).