period

period

[peer-ee-uhd]
period: see punctuation.
period, in physics: see harmonic motion; wave.
period, unit of time on the geologic timescale. Periods are shorter than an era and longer than an epoch. Periods are of variable length, generally lasting tens of millions of years, with characteristic fossils found preserved in the sediments deposited during the period. It is also used to designate a characteristic of geologic time, such as the glacial period.

Time required for a body in the solar system to return to the same or about the same position relative to the Sun as seen from Earth. The Moon's synodic period is the time between successive recurrences of the same phase (e.g., the period between one full moon and the next). A planet's synodic period is the time required for Earth to overtake it as both go around the Sun or (in the case of fast-moving Mercury or Venus) for the other planet to overtake Earth. Seealso sidereal period.

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Time required for a celestial body in the solar system to complete one revolution with respect to the fixed stars (as observed from a fixed point outside the system). A planet's sidereal period can be calculated from its synodic period. The sidereal period of the Moon or an artificial satellite of Earth is the time it takes to return to the same position against the background of stars. Seealso day.

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In geology, the basic unit of the geologic time scale. During these spans of time, specific systems of rocks were formed. Originally, the method for defining the sequence of periods was relative; it was based on stratigraphy and paleontology. Carbon-14 dating and similar methods are now used to determine absolute ages for various periods.

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Musical genre incorporating diverse styles from Africa, eastern Europe, Asia, South and Central America, the Caribbean, and nonmainstream Western folk sources. The term was first coined largely in response to the sudden increase of recordings in non-English languages that were released in Great Britain and the United States in the 1980s, but by the early 1990s world music had become a bona fide musical genre and counterpoint to the increasingly synthetic sounds of Western pop music. Initially, African popular music and world music were virtually synonymous, and the genre's biggest stars included the Nigerians King Sunny Ade and Fela Anikulapo Kuti and the Senegalese Youssou N'Dour. Moreover, one of its earliest advocates was the Cameroonian-born Frenchman Francis Bebey. By the 21st century world music encompassed everything from Pakistani singer Nusrat Fateh Ali Khan and the pop-flamenco of the French group the Gipsy Kings to “ambient-global” projects that merged so-called ethnic voice samples with state-of-the-art rhythm programming.

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Style of U.S. popular music sung and performed primarily by African American musicians, having its roots in gospel music and rhythm and blues. The term was first used in the 1960s to describe music that combined rhythm and blues, gospel, jazz, and rock music and that was characterized by intensity of feeling and earthiness. In its earliest stages, soul music was found most commonly in the South, but many of the young singers who were to popularize it migrated to cities in the North. The founding of Motown in Detroit, Mich., and Stax-Volt in Memphis, Tenn., did much to encourage the style. Its most popular performers include James Brown, Ray Charles, Sam Cooke, and Aretha Franklin.

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or rock and roll

Musical style that arose in the U.S. in the mid-1950s and became the dominant form of popular music in the world. Though rock has used a wide variety of instruments, its basic elements are one or several vocalists, heavily amplified electric guitars (including bass, rhythm, and lead), and drums. It began as a simple style, relying on heavy, dance-oriented rhythms, uncomplicated melodies and harmonies, and lyrics sympathetic to its teenage audience's concerns—young love, the stresses of adolescence, and automobiles. Its roots lay principally in rhythm and blues (R&B) and country music. Both R&B and country existed outside the mainstream of popular music in the early 1950s, when the Cleveland disc jockey Alan Freed (1921–65) and others began programming R&B, which until then had been played only to black audiences. Freed's success gave currency to the term rock and roll. The highly rhythmic, sensual music of Chuck Berry, Bill Haley and the Comets, and particularly Elvis Presley in 1955–56 struck a responsive chord in the newly affluent postwar teenagers. In the 1960s several influences combined to lift rock out of what had already declined into a bland and mechanical format. In England, where rock's development had been slow, the Beatles and the Rolling Stones were found to have retained the freshness of its very early years and achieved enormous success in the U.S., where a new generation had grown up unaware of the musical influences of the new stars. At the same time, Bob Dylan, Joni Mitchell, the Byrds, and others were blending the traditional ballads and verse forms of folk music with rock, and musicians began to explore social and political themes. Performers such as the Grateful Dead, Jim Morrison of the Doors, and Frank Zappa of the Mothers of Invention combined imaginative lyrics with instrumental virtuosity, typically featuring lengthy solo improvisation. Janis Joplin and Jimi Hendrix won large followings with their exotic elaborations on R&B. The 1970s saw the rise of singer-songwriters such as Paul Simon, Neil Young, Elton John, David Bowie, and Bruce Springsteen, and rock assimilated other forms to produce jazz-rock, heavy metal, and punk rock. In the 1980s the disco-influenced rock of Madonna, Michael Jackson, and Prince was balanced by the post-punk “new wave” music of performers such as Laurie Anderson, Talking Heads (led by David Byrne), and the Eurythmics—all of whom illustrated their songs with music videos. By the 1990s rock music had incorporated grunge, rap, techno, and other forms.

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Popular entertainment that featured successive acts by singers, comedians, dancers, and actors. The form derived from the taproom concerts given in city taverns in England in the 18th–19th centuries. To meet the demand for entertainment for the working class, tavern owners often annexed nearby buildings as music halls, where drinking and smoking were permitted. The originator of the English music hall as such was Charles Morton, who built Morton's Canterbury Hall (1852) and Oxford Hall (1861) in London. Leading performers included Lillie Langtry, Harry Lauder (1870–1950), and Gracie Fields. Music halls evolved into larger, more respectable variety theatres, such as London's Hippodrome and the Coliseum. Variety acts combined music, comedy acts, and one-act plays and featured celebrities such as Sarah Bernhardt and Herbert Tree. Seealso vaudeville.

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German music box, with disk in playing position, from Leipzig, c. 1900

Mechanical musical instrument in which projecting pins on a revolving brass cylinder or disk, encoding a piece of music, pluck tuned steel tongues. It was probably invented circa 1780 in Switzerland. With its modular cylinders or disks, it was a popular domestic instrument until displaced by the player piano and phonograph.

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Art concerned with combining vocal or instrumental sounds for beauty of form or emotional expression, usually according to cultural standards of rhythm, melody, and, in most Western music, harmony. Music most often implies sounds with distinct pitches that are arranged into melodies and organized into patterns of rhythm and metre. The melody will usually be in a certain key or mode, and in Western music it will often suggest harmony that may be made explicit as accompanying chords or counterpoint. Music is an art that, in one guise or another, permeates every human society. It is used for such varied social purposes as ritual, worship, coordination of movement, communication, and entertainment.

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klezmer music(Yiddish; “vessel of song”)

Traditional music played by professional musicians (klezmorim) in the Jewish ghettos of eastern Europe, especially for weddings and other ceremonies. The klezmer tradition has its roots in medieval Europe. By the 19th century its style was well-developed, influenced not only by the liturgical music of the synagogue (which allows only unaccompanied singing), but also that of the local non-Jewish cultures. It is primarily lively dance music. Klezmer ensembles have varied considerably; in the U.S., where a klezmer revival began in the 1980s, a typical band consists of four to six musicians playing some combination of violin, clarinet, trumpet, trombone, tuba, accordion, double bass, and percussion.

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Music composed to accompany a play. The practice dates back to ritualistic Greek drama, and it is thus connected to the use of music in other kinds of ritual. Sometimes limited to the role of introduction or interlude (setting a mood or a historical period, for example), it may also accompany spoken dialogue (see melodrama). Film and television music is sometimes considered incidental music.

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Form of black American music derived from Pentecostal church worship services and from spiritual and blues singing. Recordings of Pentecostal preachers' sermons were immensely popular among African Americans in the 1920s. Taking the scriptural direction “Let everything that breathes praise the Lord” (Psalm 150), Pentecostal churches welcomed timbrels, pianos, banjos, guitars, other stringed instruments, and even brass into their services. Choirs often featured the extremes of female vocal range in antiphonal counterpoint with the preacher's sermon. Other forms of gospel music have included the singing and acoustic guitar playing of itinerant street preachers; individual secular performers; and harmonizing male quartets, whose acts included dance routines and stylized costumes. Gospel music's principal composers and practitioners included Thomas A. Dorsey, who coined the term; the Rev. C.A. Tindley (1851–1933); the blind wandering preacher Rev. Gary Davis (1896–1972); Sister Rosetta Tharpe (1915–73), whose performances took gospel into nightclubs and theatres in the 1930s; and Mahalia Jackson. Gospel music was a significant influence on rhythm and blues and soul music, which have in turn strongly influenced contemporary gospel music.

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Music held to be typical of a nation or ethnic group, known to all segments of its society, and preserved usually by oral tradition. Knowledge of the history and development of folk music is largely conjectural. Musical notation of folk songs and descriptions of folk music culture are occasionally encountered in historical records, but these tend to reflect primarily the literate classes' indifference or even hostility. As Christianity expanded in medieval Europe, attempts were made to suppress folk music because of its association with heathen rites and customs, and uncultivated singing styles were denigrated. During the Renaissance, new humanistic attitudes encouraged acceptance of folk music as a genre of rustic antique song, and composers made extensive use of the music; folk tunes were often used as raw material for motets and masses, and Protestant hymns borrowed from folk music. In the 17th century folk music gradually receded from the consciousness of the literate classes, but in the late 18th century it again became important to art music. In the 19th century, folk songs came to be considered a “national treasure,” on a par with cultivated poetry and song. National and regional collections were published, and the music became a means of promoting nationalistic ideologies. Since the 1890s, folk music has been collected and preserved by mechanical recordings. Publications and recordings have promoted wide interest, making possible the revival of folk music where traditional folk life and folklore are moribund. After World War II, archives of field recordings were developed throughout the world. While research has usually dealt with “authentic” (i.e., older) material not heavily influenced by urban popular music and the mass media, the influence of singer-songwriters such as Woody Guthrie, Pete Seeger, Joan Baez, and Bob Dylan expanded the genre to include original music that largely retains the form and simplicity of traditional compositions.

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Any music involving electronic processing (e.g., recording and editing on tape) and whose reproduction involves the use of loudspeakers. In the late 1940s, magnetic tape began to be used, especially in France, to modify natural sounds (playing them backward, at different speeds, etc.), creating the genre known as musique concrète. By the early 1950s, composers in Germany and the U.S. were employing assembled conglomerations of oscillators, filters, and other equipment to produce entirely new sounds. The development of voltage-controlled oscillators and filters led, in the 1950s, to the first synthesizers, which effectively standardized the assemblages and made them more flexible. No longer relying on tape editing, electronic music could now be created in real time. Since their advent in the late 1970s, personal computers have been used to control the synthesizers. Digital sampling—composing with music and sounds electronically extracted from other recordings—has largely replaced the use of oscillators as a sound source.

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or country and western

Musical style that originated among whites in rural areas of the southern and western U.S. The term country and western music was adopted by the music industry in 1949 to replace the derogatory hillbilly music. Its roots lie in the music of the European settlers of the Appalachians and other areas. In the early 1920s the genre began to be commercially recorded; Fiddlin' John Carson recorded its first hit. Radio programs such as Nashville's Grand Ole Opry and Chicago's National Barn Dance fueled its growth, and growing numbers of musicians, such as the Carter Family and Jimmie Rodgers, began performing on radio and in recording studios. With the migration of Southern whites to industrial cities in the 1930s and '40s, country music was exposed to new influences, such as blues and gospel music. Its nostalgic bias, with its lyrics about poverty, heartbreak, and homesickness, held special appeal during a time of great population shifts. In the 1930s “singing cowboy” film stars, such as Gene Autry, altered country lyrics to produce a synthetic “western” music. Other variants include western swing (see Bob Wills) and honky-tonk (see Ernest Tubb and Hank Williams). In the 1940s there was an effort to return to country's root values (see bluegrass), but commercialization proved a stronger influence, and in the 1950s and '60s country music became a huge commercial enterprise. Popular singers often recorded songs in a Nashville style, while many country music recordings employed lush orchestral backgrounds. Country music has become increasingly acceptable to urban audiences, retaining its vitality with diverse performers such as Willie Nelson, Waylon Jennings, Dolly Parton, Randy Travis, Garth Brooks, Emmylou Harris, and Lyle Lovett. Despite the influence of other styles, it has retained an unmistakable character as one of the few truly indigenous American musical styles.

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Music composed for small instrumental ensembles and performed without a conductor. Traditionally intended for performance in a room or reception hall, often solely for the performers' own pleasure, chamber music is now often heard in concert halls. It began with the 16th-century instrumental consort, and long continued to be associated with aristocratic households. The duo sonata (usually for violin and continuo) and trio sonata appeared in early 17th-century Italy. The string quartet arose in the 1750s and remains the best-known chamber genre and ensemble. The serenade, nocturne, and divertimento were Classical genres for varying instrumental forces, often intended to accompany meals and other activities. Standard ensembles include the string trio (violin, viola, cello), string quintet (two violins, two violas, cello), and piano trio (piano, violin, cello). The chamber orchestra, usually with fewer than 25 musicians, is often used for 18th-century music and usually requires a conductor. Seealso sonata.

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(from Latin, alea: “dice game”) Any 20th-century music, particularly that of the 1950s and '60s, the composition or performance of which incorporates elements of chance. In aleatory music aspects such as the ordering of a piece's sections, its rhythms, and even its pitches are decided at the moment of performance. When not purely improvising, players follow lists of arbitrary rules or interpreted “graphic” notation that merely suggest the sounds. Charles Ives and Henry Cowell had used such techniques, but John Cage became the principal figure in aleatory; other aleatory composers include Earle Brown (1926–2002), Morton Feldman (1926–87), and Pierre Boulez.

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Conservatory of music in Philadelphia, Pa., U.S. It was founded in 1924 by Mary Louise Curtis Bok (1876–1970), wife of the editor Edward Bok, and named for her father, the inventor Charles Gordon Curtis. Her endowment was adequate to assure scholarships for gifted students throughout the world. Many eminent musicians have served on its faculty, including Wanda Landowska, Bohuslav Martinů, and Rudolf Serkin. Graduates include Samuel Barber, Leonard Bernstein, and Gian Carlo Menotti.

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Period in European history traditionally dated from the fall of the Roman Empire to the dawn of the Renaissance. In the 5th century the Western Roman Empire endured declines in population, economic vitality, and the size and prominence of cities. It also was greatly affected by a dramatic migration of peoples that began in the 3rd century. In the 5th century these peoples, often called barbarians, carved new kingdoms out of the decrepit Western Empire. Over the next several centuries these kingdoms oversaw the gradual amalgamation of barbarian, Christian, and Roman cultural and political traditions. The longest-lasting of these kingdoms, that of the Franks, laid the foundation for later European states. It also produced Charlemagne, the greatest ruler of the Middle Ages, whose reign was a model for centuries to come. The collapse of Charlemagne's empire and a fresh wave of invasions led to a restructuring of medieval society. The 11th–13th centuries mark the high point of medieval civilization. The church underwent reform that strengthened the place of the pope in church and society but led to clashes between the pope and emperor. Population growth, the flourishing of towns and farms, the emergence of merchant classes, and the development of governmental bureaucracies were part of cultural and economic revival during this period. Meanwhile, thousands of knights followed the call of the church to join the Crusades. Medieval civilization reached its apex in the 13th century with the emergence of Gothic architecture, the appearance of new religious orders, and the expansion of learning and the university. The church dominated intellectual life, producing the Scholasticism of St. Thomas Aquinas. The decline of the Middle Ages resulted from the breakdown of medieval national governments, the great papal schism, the critique of medieval theology and philosophy, and economic and population collapse brought on by famine and disease.

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or Old Stone Age

Ancient technological or cultural stage characterized by the use of rudimentary chipped stone tools. During the Lower Paleolithic (circa 2,500,000–200,000 years ago), simple pebble tools and crude stone choppers were made by the earliest humans. About 700,000 years ago, the first rough hand ax appeared; it was later refined and used with other tools in the Acheulean industry. A flake-tool tradition emerged in the Middle Paleolithic, as exemplified by implements of the Mousterian industry. The Upper Paleolithic (40,000–10,000 BC) saw the emergence of more complex, specialized, and diverse regional stone-tool industries, such as the Aurignacian, Solutrean, and Magdalenian. The two principal forms of Paleolithic art are small sculptures—such as the so-called Venus figurines and various carved or shaped animal and other figures—and monumental paintings, incised designs, and reliefs on the walls of caves such as Altamira (in Spain) and Lascaux Grotto (in France). The end of the Paleolithic is marked by the emergence of the settled agricultural villages of the Neolithic Period.

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or New Stone Age

Final stage of technological development or cultural evolution among prehistoric humans. It is characterized by the use of stone tools shaped by polishing or grinding, the domestication of plants or animals, the establishment of permanent villages, and the practice of such crafts as pottery and weaving. The Neolithic followed the Paleolithic Period (and in northwestern Europe the Mesolithic) and preceded the Bronze Age. Its beginning is associated with the villages that emerged in South Asia circa 9000 BC and flourished in the Tigris and Euphrates river valleys from circa 7000 BC. Farming spread northward throughout Eurasia, reaching Britain and Scandinavia only after 3000 BC. Neolithic technologies also spread to the Indus River valley of India by 5000 BC and to the Huang Ho valley of China by circa 3500 BC. The term is not applied to the New World, though Neolithic modes of life were achieved independently there by circa 2500 BC.

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