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The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles of a spherical coordinate system: altitude and azimuth. Therefore, the horizontal coordinate system is sometimes called the az/el system, [1] the alt/az system, or the alt-azimuth system, among
Coordinate system [2] Center point (origin) Fundamental plane (0° latitude) Poles Coordinates Primary direction (0° longitude) Latitude Longitude Horizontal (also called alt-az or el-az) Observer Horizon: Zenith, nadir: Altitude (a) or elevation Azimuth (A) North or south point of horizon Equatorial: Center of the Earth (geocentric), or Sun ...
Once the radius is fixed, the three coordinates (r, θ, φ), known as a 3-tuple, provide a coordinate system on a sphere, typically called the spherical polar coordinates. The plane passing through the origin and perpendicular to the polar axis (where the polar angle is a right angle ) is called the reference plane (sometimes fundamental plane ).
Local tangent plane coordinates (LTP) are part of a spatial reference system based on the tangent plane defined by the local vertical direction and the Earth's axis of rotation. They are also known as local ellipsoidal system , [ 1 ] [ 2 ] local geodetic coordinate system , [ 3 ] local vertical, local horizontal coordinates ( LVLH ), or ...
In the largest telescopes, the mass and cost of an equatorial mount is prohibitive and they have been superseded by computer-controlled altazimuth mounts. [5] The simple structure of an altazimuth mount allows significant cost reductions, in spite of the additional cost associated with the more complex tracking and image-orienting mechanisms. [6]
Another common coordinate system for the plane is the polar coordinate system. [7] A point is chosen as the pole and a ray from this point is taken as the polar axis. For a given angle θ, there is a single line through the pole whose angle with the polar axis is θ (measured counterclockwise from the axis to the line).
The axes of the original frame are denoted as x, y, z and the axes of the rotated frame as X, Y, Z.The geometrical definition (sometimes referred to as static) begins by defining the line of nodes (N) as the intersection of the planes xy and XY (it can also be defined as the common perpendicular to the axes z and Z and then written as the vector product N = z × Z).
For satellites orbiting the Earth it is normal to use the Equatorial coordinate system. The projection of the Earth's equator onto the celestial sphere is called the celestial equator . Similarly, the projections of the Earth's north and south geographic poles become the north and south celestial poles , respectively.