Azimuth

The acimut is the angle formed between the reference address (north) and a line between the observer and a point of interest planned in the same plane as the reference address.

The azimuth, also written as azimuth (from Arabic: السمت [as-sumūt] 'the directions') (which is the plural of samt 'direction') or more rarely azimud (plural azimudes), refers to an angle of orientation on the surface of a real or virtual sphere. The precise meaning of this term has some particularities depending on the discipline in which it is used.

When used as a celestial coordinate, the azimuth is the horizon direction of a star or other astronomical object in the sky. The star is the point of interest, the reference plane is the local area (for example, a circular area with a radius of 5 km at sea level) around an observer on the Earth's surface, and the reference vector points to true north. The azimuth is the angle between the north vector and the vector of the star in the horizontal plane.

Azimuth is usually measured in degrees (°). The concept is used in navigation, astronomy, engineering, mapping, mining, and ballistics.

Etymology

The word azimuth is used in all European languages today. It originates from medieval Arabic with السموت (al-sumūt, pronounced as-sumūt), meaning "the directions" (plural from Arabic السمت al-samt = "the direction"). The Arabic word entered late medieval Latin in an astronomical context and in particular in the use of the Arabic version of the astrolabe. The first known record in any Western language is in Spanish in the 1270s in a book on astronomy that was largely derived from Arabic sources, the Libro del saber de astrologia commissioned by King Alfonso X de Castilla. Its first recorded use in English is in the 1390s in Geoffrey Chaucer's Treatise on the Astrolabe.

Astronomy

In astronomy, the azimuth is the angle or arc length measured on the celestial horizon formed by the North cardinal point and the vertical projection of the body on the horizon of the observer located at some latitude. It is measured in degrees from the North cardinal point in a clockwise direction, that is, East-South-West-North.

By vertical projection, we understand the cut with the horizon that has the great circle that passes through the zenith and the star.

It is one of two horizontal coordinates, the other being height. The height and azimuth are coordinates that depend on the position of the observer. That is to say that, at the same moment, a star is seen under different horizontal coordinates by different observers located at different points on Earth. This means that these coordinates are local.

Nautical

In navigation, the azimuth is measured from the north cardinal point clockwise from 0° to 360° and is called the true (Azv) or true azimuth. The azimuth may be magnetic, if it is measured with respect to magnetic north (Azm), or compass azimuth (Azc), in English compass, if it is measured from the north point of the compass. In the case of air navigation charts, in which the magnetic azimuth is used, it is called heading.

Azimuths measured from true north

Conversions

To convert a heading to an azimuth, you first need to know the magnetic declination. In this way, if the magnetic declination is to the East, then the azimuth will be the heading plus the magnetic declination (Az = Rm+Dm). On the other hand, if the magnetic declination is to the west, then the azimuth is equal to the heading minus the magnetic declination (Az = Rm-Dm). To facilitate the equations and use only one, the equation where the azimuth is the heading plus the magnetic declination is used, taking into account the sign convention where East is positive and West is negative. Example: I need to find the azimuth at a point where the heading is 60° and the magnetic declination is 5° West (-5°). Using the formula: Az = Rm+Dm = 60° + (-5°) = 55°.

Nautical delays

In a sailing ship, this is the name given to the angle measured "from north", clockwise, to an object (lighthouse, star, boat, etc.).
Since there is a difference between north geographic and magnetic, there is a deviation when taking the measurements of the delays to a nautical chart. It can be true bearing (Dv) or needle bearing (Da). The true bearing is the needle bearing corrected with the total correction (Ct). It is the one that is actually marked on the nautical chart.
The total correction (Ct) is the sum of the magnetic declination (dm), the difference between the geographic and magnetic north, and the needle deviation, the deviation produced by the metallic masses and apparatus of a ship (Dv=Da+Ct).
If the angle is measured from the bow of the ship it is called "bearing". If the bearing is obtained from the port side of the vessel it is negative and if it is from the starboard it is positive.
Bearings can be converted into bearings using the formula: bearing=bearing+heading.

Instruments

The taking of horizontal angles in marine vocabulary is often called "bearing". On ships, "visual bearings" are taken from gimbaled platforms that have a rotating ring (alidade) called tachometers. On gyro-equipped vessels, tachymeters often have a "repeater" of the gyrocompass, which allows the "azimuth compass" to be taken directly, to which the known error must be added, if any.

You can also take a "radar bearing" to the identified echoes. If the radar is in a "relative" presentation, that is to say that its "line of faith" is indicating the bow, the heading is added to that "bearing". If the radar is in "true" presentation, the line of faith indicates North and the azimuth is taken directly.

Cartography

In cartography, the azimuth is also measured from the north cardinal point.

It is the angle of a direction counted clockwise from geographic north. The azimuth of a point to the east is 90 degrees and to the west is 270 sexagesimal degrees. The term azimuth is only used when dealing with geographic north. When you start counting from magnetic north, it is often called heading or magnetic azimuth. In geodesy or geodetic surveying, the azimuth is used to determine the orientation of a triangulation system.

Frequently in cartography, and especially in topography, azimuths are expressed in centesimal degrees instead of using sexagesimal degrees.

In architecture it is a stone placed horizontally on two nadirs, being the third piece that is needed to make a dolmen.