Identifier: newtreatiseonpra00thomrich (find matches)
Title: A new treatise on the practice of navigation at sea : containing all the details necessary to enable the mariner to become a good practical navigator.
Year: 1902 (1900s)
Authors: Thoms, William
Subjects: Navigation Nautical astronomy
Publisher: New York : Printed for the author and sold by John Bliss & Co
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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cension is reckoned on the Celestial Equator, exactly as Longitude of places on the Earth is reckoned on the Terrestrial Equator. The first point of Aries being usedas a first Meridian, and from which the Right Ascension of all the Heavenly Bo^les are reckoned in hoursand minutes, the same as the first Meridian of Greenwich is used to reckon the Longitude from, in Degreesand Minutes. Right Ascension is therefore used in determining the places of the Heavenly Bodies, and is their distancein time from the first point of Aries. Sidereal Time begins when the first point of Aries is on the Meridian, and is counted through the 84hours, till the same point returns again, which is called a Sidereal Day, and consists of 23 hours 56 mm-Btes 4 seconds of Common or Mean Time. The Hour Angle of the first point of Aries is the Right Ascension of the Meridian. ft? NAUTICAL ASTRONOMY. DIAGRAM,Sktnnng the Motion of the Heavenly Bodies round the Pole, drawn on the Plane of tht Celestial Equal** Fig. 4.
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tK th%* Figure the Spectator ts supposed to be standing on the North Pole, facing toward tht South, havinr East on the Right hand and West on the Left. TO CONSTRUCT THE FIGURE. Take 60* from the Chords and describe a circle which will represent the Celestial Equator. Draw aperpendicular line to represent the Meridian. Make HP the first point of Aries, and mark the Hours ofRiaht Ascension round the Equator from Right to Left, according to the progression of the HeavenlyBodies, which is, from East to West. Mark the Sun, whose Right Ascension from the first point of Aries isVII h. Then the Suns Hour Angle West of the Meridian at M is 3 hours. The first point of Aries having passed the Meridian 7 hours before the Sun, the Suns Hour Angle addedto it gires X h. as the Right Ascension of the Meridian, or, as it is called, the Sidereal Time, which commences when the first point of Aries is on the Meridian, and is counted through the 24 hours, until it againcomes to the same Meridian. Suppose

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