Photoelectric Observations in Geodetic Astronomy

Abstract

The Repsold micrometer method for stellar transit observations is still used widely in geodetic astronomy; unfortunately, it is not free from “personal bias”, which introduces uncertainty in the Laplace control of triangulation networks. Until very recently, the photoelectric transit detection method was reserved for fixed observatory use because of the elaborate and power-consuming equipment needed. However, highly accurate and portable amplifiers and recorders are now readily available, enabling the geodesist to adapt this method to his own needs. This article indicates a method of obtaining accurate times of transit from analogue recordings of photoelectric observations. In Part I, analytical expressions are developed for the variation of light intensity falling on a photomultiplier, as a stellar image is occulated by a fixed line in the focal plane of the telescope. Using these analytic approximations, the expected response of an amplifier-recorder system, coupled to the photo-multiplier with r. resistance-capacitance filter, is determined. Accurate corrections to the distorted response are then obtained. The only calibration required by this method is that of the system’s time constant. In Part II, a description is given of the experimental equipment used to verify the method, and the results are discussed.