Azimuth
The azimuth is the horizontal angle between the direction of an object and a direction of reference. The term is resulting from the Spanish acimut , him even resulting from the Arab .
This reference is the true north. The azimuth is measured since north in degree of 000° with 359° in the retrograde direction (direction of the needles of a watch): thus the is is with the 90°, the Southern with the 180° and the western with the 270°.
In Navigation, the azimuth of an object is measured using a Amplitude compass. This measurement is the azimuth compass ( Zc ); the true azimuth from of deduced while making the corrections (variation, deviation, variation) due to the compass used:
- Zv = Zc + W
- W is the variation of the compass;
- if it is about a gyroscopic compass, in general W = 0 ;
- in the case of a magnetic compass W = D + δ : summon magnetic Déclinaison and deviation specific to the compass.
- W is the variation of the compass;
In Astronomy, in the horizontal Frame of reference (local system), the direction of an celestial object can be given by its astronomical azimuth , horizontal angle measured since the true north in the direction of the needles of a watch, and its Height . Let us note that many works of astronomy always count the azimuths starting from the south (the advantage is that at the time of its passage to the meridian line the azimuth and the time Angle of a star are both null). It is enough to specify selected conventions.
See too
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