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Chi Cygni (χ Cyg, χ Cygni) is a variable star of the Mira type in the constellation Cygnus. Chi Cygni shows one of the largest variations in magnitude known. Typically it brightens and fades from 5th to 13th magnitude. The average period of this brightness fluctuation is 407 days. Observed extremes were 3.3 and 14.3 respectively. Thus Chi Cygni is visible at its minimum only with telescopes larger than 30 centimeters, while at maximum brightness is easily visible to the naked eye. Its distance is approximately 600 light years. The astronomer Gottfried Kirch discovered its variability in 1686. Thomas Dick, LL.D, writes: "The period of this star has been settled by Maraldi and Cassini at 405 days; but from a mean of the observations of Mr. Pigot, it appears to be only 392, or at most 396-7/8 days. "The particulars relating to it are, #When at its full brightness, it undergoes no perceptible change for a fortnight. #It is about three and a half months in increasing from the eleventh magnitude to its full brightness, and the same in decreasing; for which reason it may be considered as invisible during six months. #It does not always attain the same degree of lustre, being sometimes of the 5th and sometimes of the seventh magnitude. "It is situated in the neck (the Swan constellation ), and nearly equi-distant from ''Beta'' and ''Gamma'', and south by west from ''Deneb'', at the distance of about twelve degrees, and is marked ''Chi''." ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chi Cygni」の詳細全文を読む スポンサード リンク
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