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Articles

1980: Vol. LVII, No. 2

From Ephemeris to Epetis

Submitted
August 6, 2015
Published
2015-07-13

Abstract

Geographic positioning invariably implies solving “ triangles of position". On the celestial sphere, the angles of a triangle are the celestial pole, the observer’s zenith and the zenith of either a terrestrial mark or a celestial point. I do not propose to elaborate on this fact since it is one well known to navigators and geodesists, but only to point out the singularity of the situation. In astronomic positioning the celestial point (**) has by definition the corresponding star’s hourly angle at the meridian of origin as Longitude and the sta r’s declination as Latitude. The distance and bearing of this point are deduced from the star’s height and azimuth. No difficulties are posed by the fact that this point is mobile, provided the hourly coordinates of the star at the time of the observation can be determined.