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A nocturnal is an instrument used to determine the local time based on the relative positions of two or more stars in the night sky. Sometimes called a "horologium nocturnum" (time instrument for night) or nocturlabe (in French and occasionally used by English writers), it is related to the astrolabe and sun dial. Knowing the time is important in piloting for calculating tides and some nocturnals incorporate tide charts for important ports. Even if the nightly course of the stars has been known since antiquity, the mentions of a dedicated instrument for its measurement are not found before the Middle Ages. The earlier image presenting the use of a nocturnal is in a manuscript dated from the 12th century.〔Farre i Olive E., (1996): ''La Sphaera Horarum Noctis de Ramon Llull'', "La Busca de Paper" n. 22, Primavera, p. 3-12 (edicion bilingue)〕 Raymond Lull repeatedly described the use of a ''sphaera horarum noctis'' ou ''astrolabium nocturnum''.〔Raimon Lull, ''Liber Principorum medicinae'' in ''Opera omnia'', vol.1, Chap. 36, par.30, Mainz, 1721; Earlier Lull mentions the nocturnal in his ''Nova geometria'' (1299)〕 With Martín Cortés de Albacar's book ''Arte de Navegar'', published in 1551 the name and the instrument gained a larger popularity〔Harriet Wynter and Anthony Turner, ''Scientific Instruments'', Studio Vista, 1975, ISBN 0-289-70403-0〕 It was described also c. 1530 by Peter Apianus in his ''Cosmographicus Liber'' republished later by Gemma Frisius with a widely circulated illustration of the instrument while being used by an observer. ==Construction== Nocturnals have been most commonly constructed of wood or brass. A nocturnal will have an outer disc marked with the months of the year, and an inner disc marked with hours (and perhaps half hours, or quarter hours on the largest instruments) as well as locations for one or more reference stars. It will also have a pointer rotating on the same axis as the discs, sometimes extended beyond the rim. The axis, or pivot point, must be such that a star can be sighted through it; usually a hollow rivet is used. Since the instrument is used at night, markings may be exaggerated or raised. Often the inner disc has a diagram of the necessary constellations and stars, to aid in locating them. 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「Nocturnal (instrument)」の詳細全文を読む スポンサード リンク
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