The horizontal coordinate system describes a direction by its altitude above the astronomical horizon and its azimuth. Always specify the origin and orientation of azimuth.
For a spherical Earth, geographical latitude is the angle of the local vertical above the equatorial plane. It equals the altitude of the north celestial pole in the northern hemisphere. Precision astrometry distinguishes geodetic and astronomical latitude.
Azimuth is the angle about the local vertical measured in the astronomical horizon. A common convention increases eastward from north; some astronomical formulae use westward from north. The convention changes the sign in the hour angle transformation.
The zenith is the direction of the local upward vertical on the celestial sphere. Azimuth is undefined there.
The astronomical horizon is the great circle perpendicular to the local vertical. It is a geometric horizon, distinct from a terrain boundary or an apparent refracted horizon.
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The Horizontal Coordinate System, also known as the Altitude/Azimuth Coordinate System, is a locally defined system used in astronomy to specify the position of celestial objects in the sky as viewed from a particular location on Earth at a specific time. ### Key Components: 1. **Altitude (Alt)**: - The angle measured from the observer's local horizon to the object in the sky.