Stellar triangulation is a method of geodesy and of its subdiscipline space geodesy used to measure Earth's geometric shape. Stars were first used for this purpose by the Finnish astronomer Yrjö Väisälä in 1959, who made astrometric photographs of the night sky at two stations together with a lighted balloon probe between them.
Even this first step showed the potential of the method, as Väisälä got the azimuth between Helsinki and Turku (a distance of 150 km) with an accuracy of 1″. Soon the method was successfully tested by ballistic rockets and for some special satellites.
