isogonic lines

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Isogonic Lines

 

the isolines of the orientation of any physical variable.

In meteorology, isogonic lines are lines of identical wind direction. In terrestrial magnetism, isogonic lines are lines where the values of magnetic declination are equal. On magnetic maps, isogonic lines in the middle latitudes move in an approximately meridional direction, with the exception of eastern Asia, where they are closed. In higher latitudes isogonic lines converge toward the geographic and magnetic poles. Astronomy deals with the isogonic lines of a solar eclipse—the lines passing through the points on the earth’s surface from which the lines from the center of the sun to the pointsat which the darkened lunar disc touches the bright solar disc at the beginning and end of a partial eclipse have the same position angle. Isogonic lines are calculated in advance and used in setting up observations of solar eclipses.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

isogonic lines

Irregular lines across an aeronautical chart, along which the magnetic north and true north are separated by a given angle. This angle is known as a compass variation.

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