Algol

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Algol

(ăl`gŏl), famous variable starvariable star,
star that varies, either periodically or irregularly, in the intensity of the light it emits. Other physical changes are usually correlated with the fluctuations in brightness, such as pulsations in size, ejection of matter, and changes in spectral type, color, or
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 in the constellation PerseusPerseus,
in astronomy, northern constellation lying E of Cassiopeia and N of Taurus. It contains the bright star Mirfak (Alpha Persei) and Algol (Beta Persei), a visible variable star of the type known as an eclipsing variable.
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; Bayer designation β Persei; 1992 position R.A. 3h07.7m, Dec. +40°55'. Algol's variation in apparent magnitudemagnitude,
in astronomy, measure of the brightness of a star or other celestial object. The stars cataloged by Ptolemy (2d cent. A.D.), all visible with the unaided eye, were ranked on a brightness scale such that the brightest stars were of 1st magnitude and the dimmest stars
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, from 2.06 to 3.28, is due to the fact that it is an eclipsing binary starbinary star
or binary system,
pair of stars that are held together by their mutual gravitational attraction and revolve about their common center of mass. In 1650 Riccioli made the first binary system discovery, that of the middle star in the Big Dipper's handle, Zeta
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, with one component revolving about the other with a period of 2 days, 20 hr, 49 min. Because the plane of revolution is almost parallel to the line of sight, the star dims noticeably when the dimmer component passes in front of, or eclipses, the brighter component, and dims again very slightly when the brighter component eclipses the dimmer one (see eclipseeclipse
[Gr.,=failing], in astronomy, partial or total obscuring of one celestial body by the shadow of another. Best known are the lunar eclipses, which occur when the earth blocks the sun's light from the moon, and solar eclipses, occurring when the moon blocks the sun's light
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); the primary minimum, when the brighter component is eclipsed, lasts about 10 hr. Algol is of spectral classspectral class,
in astronomy, a classification of the stars by their spectrum and luminosity. In 1885, E. C. Pickering began the first extensive attempt to classify the stars spectroscopically.
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 B8 V and is about 105 light-years from the earth. The name Algol comes from the Arabic Ras al Ghul, which means "demon's head," and the star is sometimes called the Demon Star.

ALGOL:

see programming languageprogramming language,
syntax, grammar, and symbols or words used to give instructions to a computer. Development of Low-Level Languages

All computers operate by following machine language programs, a long sequence of instructions called machine code that is
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.
Algolclick for a larger image
Algol: light curve of Algol.

Algol

(al -gol) (Demon Star; Winking Demon; β Per) A white star that is the second-brightest one in the constellation Perseus. It was the first eclipsing binary to be discovered, being the prototype of the Algol variables, although its variations in brightness were known to early astronomers. The theory of a darker companion periodically cutting off the light of the brighter star (Goodricke, 1782; Pickering, 1880) was confirmed spectroscopically in 1889. The brighter star (Algol A) is about three times the Sun's diameter; the fainter orange 3rd-magnitude companion (Algol B) is about 20% larger. The two stars revolve about one another in a period of 68.8 hours, and the eclipses cause the magnitude to drop from 2.2 to 3.5 (see illustration). There is also a third more distant star, Algol C, which orbits Algol A and B in 1.86 years.

Algol A is about 3.7 times as massive as the Sun, while Algol B has a mass of only 0.8 solar masses. According to stellar evolution theory, a more massive star evolves more rapidly; yet in the Algol system the more massive Algol A is still a main-sequence star while Algol B has evolved to become a subgiant. This is the Algol paradox, which is explained by slow and continuous mass transfer from Algol B to Algol A (see Algol variables). This mass transfer, along with apsidal motion, accounts for slight changes in the time of Algol's eclipses. The streams of gas passing from Algol B to Algol A make Algol an erratic radio and X-ray source. mv : 2.1 (A), 3.5 (B); Mv : –0.2 (A), 1.2 (B); spectral type: B8 V (A), K0 IV (B); distance: 29 pc.

Algol

 

an abbreviated name denoting a series of programming languages formed from the initial letters of the English words “algorithmic” and “language.” ALGOL was devised by an international group of scientists in 1958–60. The final form of the language, as adopted by an international conference of January 1960 in Paris, was given the name ALGOL-60 to distinguish it from the initial version, called ALGOL-58.

The basic symbols of ALGOL are decimal digits, upper and lowercase letters of the alphabet, punctuation marks, symbols of mathematical and logical operations, and various other special signs, as well as certain English words (in particular, “begin” and “end”). From the basic ALGOL symbols, following definite rules, constructions are formed —numbers and expressions (arithmetic, logical, and others), descriptions, notes, and operators; these operators, in turn, in combination with the basic symbols, combine to form more complicated operators, and so on. An algorithm assigned in ALGOL is a so-called ALGOL program. With the help of a second special program it is transformed into a program in the language of the particular digital computer.

REFERENCES

Algoritmicheskii iazyk ALGOL-60. Moscow, 1965. (Translated from English.)
Lavrov, S. S. Universalnyi iazykprogrammirovaniia (ALGOL-60), 2nd ed. Moscow, 1967.

Algol

[′al‚gȯl]
(astronomy)
An eclipsing variable star of spectral classification B8 in the constellation Perseus; the star β Persei. Also known as Demon Star.
(computer science)
An algorithmic and procedure-oriented computer language used principally in the programming of scientific problems.

ALGOL

ALGOL

(ALGOrithmic Language) A high-level programming language that was developed as an international language for the expression of algorithms between people and between people and machines. ALGOL-60 (1960) was simple and widely used in Europe. ALGOL-68 (1968) was more complicated and scarcely used, but was the inspiration for Pascal. The following example changes Fahrenheit to Celsius. See Pascal.

 fahrenheit
 begin
  real fahr;
  print ("Enter Fahrenheit ");
  read (fahr);
  print ("Celsius is ",(fahr-32.0)*5.0/9.0);
 end
 finish