How did gravity build astronomical objects that rotate? It seems to me a safe bet, supported in part by observation, that the heterogeneous assembly of known astronomical objects comprising the observed universe, whose contents range from minor planets (one named for my mother) to the recently imaged remote galaxies observed by the Hubble telescope, and are all busily revolving or rotating. I’d like to understand, in broad terms, how this conglomerate, believed to have started out as a hot, dense, nearly homogeneous fluid some 13.7 billion years ago, became so heterogeneous and accumulated so much locally stored angular momentum. The short answer that “Gravitational condensation did it” doesn’t quite satisfy me, although it is of course correct. In struggling to gain a better understanding for myself of the fundamentals of structure formation, without relying on computer modelling done by others, I’ve had the thought that fluid shear must have been an important aspect of the process. The elastic or plastic shear of solids is reasonably well understood, but involves descriptions of shear appropriate only for uniform deformation, like pure shear (described by a symmetric second-rank tensor) and engineering or simple shear (described as the sum of a pure shear and a rotation). In an astronomical context the dynamic behaviour of fluids within larger host structures involves more complicated shearing deformations and motions, as in gravitating gases and gravitating particulate fluids; like the rings of Saturn, interstellar dust clouds (Orion Nebula) or, on a larger scale, the star clouds in the central Milky Way. I suppose that even galaxies in clusters (e.g. Fornax) are likely to be collectively sheared by gravity. The conclusion I’ve come to is that: “Gravitational condensation was aided in creating a heterogeneous universe of rotating and revolving structures, which on different scales store angular momentum, by its central-force character that generates Keplerian shear, which can causes matter to rotate and revolve.” Is this oversimplified guess anywhere near correct? And, finally, since tonight (30 September) is Full Moon, let me ask: does the Moon always present the same appearance to us because Keplerian shear stresses the Earth produces, acting on the Moon, partly compensate for the centripetal stresses generated by the Moon’s 28-day periods of axial rotation and Earth-orbit revolving?