Surveys and Star Counts: The Kapteyn Legacy

Abstract

Modern survey technology and databases vastly exceed Kapteyn’s ambitions for his liftime: yet modern research techniques are still built on the methodologies Kapteyn developed, have the strengths and weaknesses he understood, and, remarkably, are largely still addressing the same questions. Galaxy surveys, where complemented by large radial velocity programs, are beginning to map the large scale structure of the Universe in a reliable way. Stellar photometric surveys, covering many wavelengths, and so determining interstellar extinction, and quantifying several percent of all the stars in the Milky Way, now outline reliably the general structural features of the Galaxy, dust permitting. Deduction of the physical processes which have led to the present Galaxy is however still impossible, since, as did Kapteyn, we lack a reliable and accurate proper motion, parallax and radial velocity census. Next generation astrometric and photometric space missions will finally be able to achieve Kapteyn’s scientific aims.