astronomical triangle

Astronomical triangle

astronomical triangle

A spherical triangle on the celestial sphere formed by the intersection of the great circles joining a celestial body, S, the observer's zenith, Z, and the north (or south) celestial pole, P (see illustration). The relationships between the angles and sides of a spherical triangle are used for transformation between equatorial and horizontal coordinate systems: the angle at S (q) is the parallactic angle; that at P (t) is the hour angle of S; that at Z (A) is the azimuth of S. The sides are equal to the zenith distance (ζ), the complement of the terrestrial latitude (90°–⊂), and the complement of the declination (90°–δ). The parallactic angle, for example, is given by the sine rule:

sin q = (cos ⊂ sin t )/sin ζ = (cos ⊂ sin A )/cos δ

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

astronomical triangle

[‚as·trə′näm·ə·kəl ′trī‚aŋ·gəl]

(astronomy)

A spherical triangle on the celestial sphere.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

astronomical triangle

The spherical triangle formed by joining the observer's elevated pole, his zenith, and the position of the body on the celestial sphere.

An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved