A century of existence: it may seem short on the time-scale of the evolution of the universe, but very consequential to that of a scientific association. The fact that the IAU may be able to celebrate such a milestone is in itself a meritorious collective achievement, for it was not obvious at the very beginning that this organization was going to last more than a decade. Drawing on the historical sociology of scientific institutions, my paper will discuss the moral economy through which the IAU – and its dated but persistent form of scientific internationalism – has stabilized and maintained its identity since its creation in 1919, under the unifying auspices of a global scientific object to be known as: Under One Sky.
