)
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
[′al‚gȯl]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
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.