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Azimuth

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An azimuth is a horizontal angle that defines a specific direction. It is measured from a chosen reference direction on a flat plane. In most cases, this reference is true north. The azimuth tells an observer which way to face to see a target. This target could be a star in the sky or a mountain on the horizon.

Azimuth-Altitude schematic
Azimuth-Altitude schematic

To understand the mechanism, imagine a coordinate system centered on you. You are the origin of this system. To find the azimuth of a distant object, you project a line from yourself to that object. This line is then projected perpendicularly onto a horizontal reference plane. The angle between your north reference vector and this projected line is the azimuth. In astronomy, this is one of two main coordinates. The other is altitude, which measures how high an object is above the horizon.

Brunton
Brunton

Azimuths can be expressed using different mathematical ranges. Most commonly, they use a positive range from 0° to 360°. In this system, moving clockwise from north gives you specific values. East is at 90°, south is at 180°, and west is at 270°. Another way to write it is using a signed range from -180° to +180°. Some systems also use other angular units, such as grads or mils. While north is the standard zero, any direction can be a reference if it is clearly defined.

True North Mount Allen.fw
True North Mount Allen.fw

Navigators sometimes use a different method called a bearing. A bearing might be written as S30°E. This tells you to start at south and turn 30 degrees toward the east. In this specific notation, the reference direction is stated first. The direction of the turn is stated last. This method ensures the angle stays positive between zero and 90 degrees. If a direction is exactly on a cardinal point, people simply say "due east" or "due south."

Bearing and azimuth along the geodesic
Bearing and azimuth along the geodesic

The history of the term is rooted in medieval science. The word azimuth comes from the Arabic word al-sumūt, which means "the directions." It entered late medieval Latin through the study of astronomy. This happened specifically through the use of the astrolabe, an ancient astronomical instrument. The first known record in a Western language was in Spanish in the 1270s. This was in a book called Libros del saber de astronomía. This book was commissioned by King Alfonso X of Castile and was largely based on Arabic sources. In English, the first recorded use was in the 1390s by Geoffrey Chaucer.

Brunton
Brunton

In the field of geodesy, azimuths become more complex due to the shape of the Earth. Because the Earth is an oblate spheroid, it is slightly squashed rather than a perfect sphere. This leads to two distinct types of azimuths. The first is the normal-section azimuth. This is measured by a theodolite with an axis perpendicular to the surface. The second is the geodetic azimuth, also called the geodesic azimuth. This is the angle between north and the shortest path on the surface of the spheroid. For distances under 100 km, the difference between these two is usually less than 0.03 arc seconds.

Bearing and azimuth along the geodesic
Bearing and azimuth along the geodesic

Azimuth is also a vital concept in cartography and mapping. Cartographers use azimuthal map projections to create different types of charts. These projections have a special property: they preserve directions from a central point. This makes them very useful for certain types of navigation. In math, the azimuth is related to polar, cylindrical, and spherical coordinates. In a mathematical polar coordinate system, the angle is often measured anticlockwise from the x-axis. This is a key difference from the clockwise measurement used in land navigation.

Azimuth-Altitude schematic
Azimuth-Altitude schematic
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🖼️ Images & Media (4)
File:Azimuth-Altitude schematic.svg
Azimuth-Altitude schematic.svg
File:True North Mount Allen.fw.png
True North Mount Allen.fw.png
File:Bearing and azimuth along the geodesic.png
Bearing and azimuth along the geodesic.png
File:Brunton.JPG
Brunton.JPG
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