Talcott Method

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 It might be outdated or ideologically biased.

Talcott Method


a method for measuring the astronomical latitude ϕ of a point. The method involves measuring with the eyepiece micrometer of an astronomical instrument the small (16’–20’) difference Δz between the zenrth distances of two stars, one south and one north of the zenith, at the moment the stars pass across the meridian plane. The method was proposed by the Danish astronomer P. Horrebow in 1740. It is named after the American geodesist A. Talcott, who developed its practical implementation in 1857.

If both stars are at upper transit, then

If the northern star is at lower transit, then

Here, δs is the declination of the southern star, δN is the declination of the northern star, zs is the zenith distance of the southern star, and zN is the zenith distance of the northern star. In addition, corrections may be made, for example, for the Talcott level (for the change in inclination of the telescope when it is rotated by 180°), for the difference in refractions ρs and ρN in the directions of the southern and northern stars, and for the curvature of the diurnal circle.

The Talcott method is widely used in astronomical determinations of the first class and in the work of the Latitude Service in the USSR and abroad at latitudes of up to 65°.


Kuznetsov, A. N. Geodezicheskaia astronomiia. Moscow, 1966.
Uralov, S. S. Obshchaia leoriia metodov geodezkheskoi astronomii. Moscow, 1973.


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