A surveyor in the sky

Abstract

This article is both a scientific account and a personal testimony about the development of modern astrometry. Erik Høg describes how accurete measurements of star positions have evolved from classical meridian circles to advanced satellite missions. The article follows a fascinating research journey from the early observations in Brorfelde to the development of ESA's Hipparcos satellite, which revolutionized the measurement of stars' distances and motions. Along the way, it explains how new technologies—especially photoelectric recording and computer-based data analysis—made it possible to dramatically increase measurement accuracy. Høg also describes the organizational and technical challenges of realizing an astrometric satellite and the crucial contributions from international collaborations. At the same time, the article provides a historical perspective on how accurate position measurements are fundamental to almost all branches of astronomy. Finally, Høg points forward to the ESA mission Gaia, which is expected to deliver a star catalog on an unprecedented scale and with great precision and accuracy.