1911 Encyclopædia Britannica/Cygnus
CYGNUS (“The Swan”), in astronomy, a constellation of the northern hemisphere, mentioned by Eudoxus (4th century B.C.) and Aratus (3rd century B.C.), and fabled by the Greeks to be the swan in the form of which Zeus seduced Leda. Ptolemy catalogued 19 stars, Tycho Brahe 18, and Hevelius 47. In this constellation β Cygni is a fine coloured double star, consisting of a yellow star, magnitude 3, and a blue star, magnitude 5½. The fine double star, µ Cygni, separated by Sir William Herschel in 1779, has magnitudes 4 and 5; it has a companion, of magnitude 7½, which, however, does not form part of the system. A double star, 61 Cygni, of magnitudes 5.3 and 5.9, was the first star whose distance was determined; its parallax is 0".39, and it is therefore the nearest star in the northern hemisphere with the exception of σ Centauri. A regular variable, χ Cygni, has extreme magnitudes of 5 to 13.5, and its period is 406 days. Nova Cygni is a “new” star discovered by Johann Schmidt in 1876. There is also an extended nebula in the constellation.