Geodetic Astronomy

Question 1

“The scientific study of the universe beyond the earth~ especially the observation, calculation, and theoretical interpretation of the positions, dimensions, distribution~ motion, composition, and evolution of celestial bodies and phenomena”. (Morris, 1975).

Answer 1

Astronomy

Question 2

The art and science for determining, by astronomical observations, the positions of points on the earth and the azimuths of the geodetic lines connecting such points. (Mueller, 1969)

Answer 2

Geodetic Astronomy

Question 3

Why study Geodetic Astronomy? (10)

Answer 3

(1) Knowledge of celestial coordinate systems, transformations amongst them, and variations in each of them
(2) Celestial coordinate systems define the link between satellite and terrestrial coordinate systems
(3) The concepts of time for geodetic purposes are developed
(4) Tidal studies require a knowledge of geodetic astronomy
(5) When dealing with new technologies (e.g. inertial survey systems) an understanding of the local astronomic coordinate system is essential
(6) Astronomic coordinates of terrain points, which are expressed in a “natural” coordinate system, are important when studying 3-D terrestrial networks
(7) Astronomically determined azimuths provide orientation for terrestrial networks
(8) The determination of astrogeodetic deflections of the vertical are useful for geoid determination, which in turn may be required for the rigorous treatment of terrestrial observations such as distances, directions, and angles
(9) Geodetic astronomy is useful for the determination of the origin and orientation of independent surveys in remote regions
(10) Geodetic astronomy is essential for the demarcation of astronomically defined boundaries

Question 4

Angle between the astronomic normal (gravity normal), tangent to the plumbline at the point of interest, and the plane of the instantaneous equator measured in the meridian plane.

Answer 4

Astronomic Latitude (Φ)

Question 5

Angle between the Greenwich Mean Astronomic Meridian and the astronomic meridian plane measured in the plane of the instantaneous equator

Answer 5

Astronomic Longitude (^)

Question 6

Height of the point of interest .above the geoid, measured along the plumbline, as obtained from spirit leveling and en route gravity observations

Answer 6

Orthometric Height (H)

Question 7

The distance between the geoid and a reference ellipsoid, measured along an ellipsoidal normal.

Answer 7

Geoidal Height (N)

Question 8

On the surface of a reference ellipsoid, it is the clockwise angle from north between the geodetic meridian of i and the tangent to the ellipsoidal surface curve of shortest distance (the geodesic) between i and j.

Answer 8

Geodetic Azimuth (α)

Question 9

Angle between the astronomic meridian plane of i and the astronomic normal plane of i through j, measured clockwise from north.

Answer 9

Astronomic Azimuth (A)