Meridian Circle Astrometry at the U. S. Naval Observatory

Abstract

For 150 years meridian circles have played an essential part in the mission of the U. S. Naval Observatory (USNO) in its dual role as a naval observatory, in support of celestial navigation, and as a national observatory, improving the celestial reference frame of fundamental astronomy. Examining two 20th century USNO instruments, we depict meridian circles as multiple ensembles: of sets of supporting devices, of calibrations and reductions for precision, of collected observations forming catalogues of stars, and of multiple meridian circles cooperating to solve astronomical goals and to map the heavens from pole to pole. We end briefly summarizing the contributions of the USNO meridian circles in the satellite era, with some implications for astrophysics and cosmology.