A method primarily of determining geodetic azimuths from astronomical observations, by measuring the angle θ' between a star and the marker of interest, the star and marker being at large zenith distances z* and z_m, respectively. The difference between measured angle θ'and the corresponding angle θ in a geodetic coordinate system is θ' - θ = cotz* (y cos A* - x sin A*) - cot z_m (y cos A_m - x sin A_m) where x and y are the deflections of the vertical in the meridian and in the prime vertical, respectively; A* and A_mm are the astronomic azimuths of the star and marker, respectively. The astronomic azimuth of the star is given by A* = sinφ cot H - tanδ cosφ cosec H, where φ is the latitude of the observer and H and δ are the hour angle and the declination, respectively, of the star. At large zenith distances, θ'- θ is very small, and the geodetic azimuth is given closely by the second equation. If it is not small, three or more observations are made on different stars to determine x and y also. The method is particularly useful at high latitudes. The method has also been used to determine astronomic latitude and longitude.