Alpha Centauri Triple star in the constellation Centaurus, the faintest component of which, Proxima Centauri, is currently the closest star to the Sun (about 4.2 light-years away). The two brighter components are about 0.2 light-year farther from the Sun. As seen from Earth, the system is the third brightest star (after Sirius and Canopus); Proxima is indistinguish¬ able as a separate star to the unaided eye. Alpha Centauri can be seen from Earth’s surface only from points south of about 40° N.
alpha decay Type of radioactive disintegration (see radioactivity) in which some unstable atomic nuclei dissipate excess energy by spontane¬ ously ejecting an alpha particle. Alpha particles have two positive charges and a mass of four atomic mass units; they are identical to helium nuclei. Though they are emitted at speeds about one-tenth that of light, they are not very penetrating and have ranges in air of about 1-4 in. (2.5-10 cm). Alpha decay commonly occurs in elements with atomic numbers greater than 83 (bismuth), but can occur in some rare-earth elements in the atomic-number range of 60 (neodymium) to 71 (lutetium). Alpha decay half-lives range from about a microsecond (10 -6 second) to billions of years (10 17 seconds).
alphabet Set of symbols or characters that represent language’s sounds in writing. Each character usually represents a simple vowel, a diphthong (two vowels), or one or two consonants. A writing system in which one character represents a whole syllable is called a syllabary. The first alpha¬ bet is believed to have been the North Semitic, which originated in the eastern Mediterranean region between 1700 and 1500 bc. Alphabets that arose in the next 500 years included the Canaanite and Aramaic, from which the modern Hebrew and Arabic alphabets descended, and the Greek (ancestor of the Latin alphabet), considered the first true alphabet because it includes both consonants and vowels. Scholars have attempted to estab¬ lish an exact correspondence between each sound and its symbol in new alphabets such as the International Phonetic Alphabet.
Alpheus \al-'fe-3s\ River River, southern Greece. About 75 mi (120 km) long, it is the longest river in the Peloponnese. It rises in Arcadia and flows northwest through southern Elias into the Ionian Sea. Olympia is on its northern bank. It shares its name with the ancient river god, and it figures in Greek legend, including Hercules’ cleaning of the Augean stables, and in Samuel Taylor Coleridge’s poem “Kubla Khan.”
Alpine orogeny \o-'ra-j3-ne\ Mountain-building event that affected a broad segment of southern Europe and the Mediterranean region during the middle Tertiary period. It produced intense metamorphism, crumpling of rock strata, and uplift accompanied by faulting. It was responsible for the elevation of the present Alps, from which the name derives, the uplifting of plateaus in the Balkan Peninsula and in Corsica and Sardinia, and vol¬ canic activity in England, France, Iceland, and parts of Italy.
Alpine skiing Class of competitive ski events consisting of speed events (the downhill and the supergiant slalom) and technical events (the slalom and giant slalom). Speed events are contested in single runs down longer, steeper, faster courses, with fewer turns than those featured in the technical events. Alpine skiing was first included in the Olympic Games in 1936. See also cross-country skiing; Nordic skiing.
Alps Mountain system, south-central Europe. The Alps extend in a cres¬ cent about 750 mi (1,200 km) from the Mediterranean coast between France and Italy to Vienna and cover more than 80,000 sq mi (207,000 sq km). Several peaks rise above 10,000 ft (3,000 m); the highest is Mont Banc. The Alps form a divide between the Atlantic Ocean, the Mediter¬ ranean Sea, and the Black Sea and give rise to several major European rivers, including the Rhone, Danube, and Po. Glaciers cover about 1,500 sq mi (3,900 sq km), mostly at elevations above 10,000 ft (3,000 m). The Saint Gotthard Pass is one of the Alps’s notable tunnels. Grenoble, Inns¬ bruck, and Bolzano are major Alpine cities.
Alsace-Lorraine \al-'sas-l6-Tan\ Area, eastern France. It is now usu¬ ally considered to include the present-day French departments of Haut- Rhin, Bas-Rhin, and Moselle. The area was ceded by France to Germany
© 2006 Encyclopaedia Britannica, Inc.
Alsatian ► alternator I 53
in 1871 after the Franco-Prussian War. It was returned to France after World War I, occupied by the Germans in World War II, then again restored to France. French prewar governmental policies that had clashed with the region’s particularism have since been modified. The German dialect known as Alsatian remains the lingua franca, and both French and German are taught in the schools.
Alsatian See German shepherd
Altai Mountains Russian Altay \al-'t!\ Chinese Altay Shan
\al-'tl-'shan\ Mongol Altayn Nuruu Mountain system, Central Asia. The range extends about 1,200 mi (2,000 km) in a southeast-northwest direction from the Gobi Desert to the West Siberian Plain, through parts of China, Mongolia, Russia, and Kazakhstan. The highest point is the Russian peak Belukha, 14,783 ft (4,506 m) in elevation. The mountains are the source of the Irtysh and Ob rivers and are notable for their mining and hydroelectrical potential.
Altaic \al-'ta-ik\ languages Group of more than 50 languages, com¬ prising the Turkic, Mongolian, and Manchu-Tungus subfamilies. Altaic lan¬ guages are spoken across Eurasia by more than 140 million people (the overwhelming majority of whom speak Turkic languages). Most scholars consider Altaic itself to be a family, of proven genetic relationship, though a minority attribute similarities in the languages to borrowings and areal convergence. The Uralic and Altaic language families were once believed to form a superfamily, but reliable sound correspondences have not been demonstrated, and the numerous similarities between the two are now attributed to areal influences.
Altamira \,al-t3-'mir-3\ Cave near Santander, northern Spain, famous for its magnificent prehistoric paintings and engravings. The paintings, dating to 14,000-12,000 bc, were first described in 1880. Altamira cave is 890 ft (270 m) long. The roof of the main chamber is covered with paintings, chiefly of bison, in vivid red, black, and violet. Other figures, in a simpler style, include wild boars, horses, and a hind, as well as eight engraved anthropomorphic figures and various handprints and hand out¬ lines. Engraved artifacts and other material remains suggest that the site may have been a centre for seasonal gatherings. See also Magdalenian culture; rock art.
Alton \'al-tan\ or Anda \'an-da\ (d. 1583, Mongolia) Mongol khan who terrorized China in the 16th century. He established a Chinese-style gov¬ ernment in his homeland and concluded a peace treaty with Ming-dynasty China in 1571. He converted the Mongols to the reformed, or Dge-lugs- pa, sect of Tibetan Buddhism. In 1578 Altan granted the head of the sect the title of Dalai Lama. With Mongol military aid, later Dalai Lamas crushed the more established Karma-pa (Red Hat) sect in Tibet to become Tibet’s spiritual and temporal rulers. See also Gtsang dynasty.
altar Raised structure or place used for sacrifice, worship, or prayer. Altars probably originated with the belief that objects or places (e.g., a tree or spring) were inhabited by spirits or deities worthy of prayers or gifts. Sacrifice to deities required a structure on which the victim could be killed and blood channeled off or flesh burned. In ancient Israel, the altar was a rectangular stone with a hollo wed-out basin on top. The ancient Greeks placed altars (see baetylus) in homes, marketplaces, public build¬ ings, and sacred groves. Roman altars were similarly ubiquitous and were often decorated with relief sculptures. Christians at first did not use altars, but by the 3rd century the table on which the Eucharist was celebrated was regarded as an altar. It became the focus of the mass in Christian churches and in Western churches was often adorned by a baldachin and an ALTARPIECE.