The last meridian circles: An epilogue

Abstract

The aim is to document the last 35 years of meridian circles, a type of instrument with a fundamental role in astronomy for a very long time, and to do so while witnesses are still alive and can contribute. Meridian circles provided fundamental star positions for centuries. These positions were tied to a well-defined celestial coordinate system of right ascension and declination, and accurate proper motions ensured the transformation of the positions over long periods of time. This function of the meridian circles has been taken over by space astrometry and VLBI, Very Long Baseline Interferometry. The Hipparcos astrometric satellite was approved by ESA, the European Space Agency, in 1980 and launched to a successful 3-year mission in 1989. Its successor, Gaia, completed a mission of 10.5 years in January 2025. An account is given of the last 18 meridian instruments, which were active for some part of the 35 years between 1980 and 2015. This account was made possible by input kindly supplied in correspondence with many colleagues.