azimuth

[In Dut., Ger., & Sp. azimuth; Fr. & Port. azimut; Ital. azzimutto; from Arab. a amt, pl. as- sumût = a way, a path.] [ZENITH.] Astronomy: 1. Sing .: "The angular distance of a celestial object from the north or south point of the horizon (according as it is the north or south pole which is elevated), when the object is referred to the horizon by a vertical circle." Or "the angle comprised between two vertical planes, one pa ing through the elevated pole, the other through the object." It is generally reckoned eastward or westward, from the north or south point for 180° either way; but Herschel prefers always reckoning it from the points of the horizon most remote from the elevated pole westward, so as to agree in its general direction with the apparent diurnal motion of the stars. Of course he therefore counts from 0° to 360°. (Herschel: Astron., 5th ed., 1858, § 103.) 2. Plural: Azimuths, called also vertical circles, are great circles intersecting each other in the zenith and nadir, and cutting the horizon at right angles in all the points thereof. On these are reckoned the altitude of the stars, and of the sun when he is not in the meridian. Magnetical Azimuth : Magnetical azimuth is an arch of the horizon, contained between the sun's azimuth circle and the magnetical meridian; or it is the apparent distance of the sun from the north or south point of the compa . azimuth and altitude instrument. An astronomical instrument designed to ascertain the altitudes and azimuths of the heavenly bodies at any particular time. It has two axes, the principal one vertical and the other horizontal; the former, therefore, corresponding to a vertical circle of the heavens, and the latter to the celestial horizon. The angles measured on the latter are therefore azimuths or differences of azimuth, and those on the former zenith distances, according as the graduation is from the upper point of the limb, or a point distant from it 90. ( Herschel : Astron., §§ 182-187.] (ALTAZIMUTH.] azimuth compa . An instrument used for finding the sun's magnetical azimuth, or the amplitude of any other heavenly body. azimuth dial. A dial, the stile or gnomon of which is at right angles to the plane of the horizon.