# Astronomic Definitions for Land Surveyors

**astronomic**– In surveying, azimuths or geographic positions determined by direct observation of the sun or a star (or stars) are known as astronomic azimuths or astronomic positions. Such astronomic determinations are always referred to the plumb line at the point of observation and not to the ellipsoid of reference.

**astronomic azimuth—**See *azimuth, astronomic. *

**astronomic bearing—**See *bearing; azimuth, astronomic. *

**astronomic control—**See *control, basic.*

**astronomic coordinates—**See *coordinates, astronomic; latitude, astronomic; longitude, astronomic.*

**astronomic equator—**See *parallel, astronomic.*

**astronomic latitude—**See *latitude, astronomic; longitude, astronomic; coordinates, **astronomic.*

**astronomic longitude—**See *longitude, astronomic; latitude, astronomic; coordinates, **astronomic.*

**astronomic meridian—**See *meridian.*

**astronomic North** [PLSS]–The local direction of the Earth’s axis of rotation as determined from celestial observations.

**astronomic parallel—**See *parallel, astronomic. *

**astronomical position—**See *position, astronomical. *

**astronomical refraction—**See *refraction, astronomical.*

**astronomical triangle—**The triangle on the celestial sphere formed by arcs of great circles connecting the celestial pole, the zenith, and a celestial body; PZS triangle. The angles of the astronomical triangles are: at the pole, the hour angle; at the celestial body, the parallactic angle; at the zenith, the azimuth angle. The sides are: pole to zenith, the co-latitude^{.}; zenith to celestial body, the zenith distance; and celestial body to pole, the polar distance.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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