1938: Retirement of Joseph Vanderlinden, a scientist at the Observatory. He played a crucial technical role in the installation of the double astrographe (a state-of-the-art instrument for asteroid detection) and the original Schmidt telescope at Uccle.

1911:  The New Zealand physicist Ernest Rutherford publishes his revolutionary theory on the structure of the atom. Drawing on the gold-foil experiment conducted with Geiger and Marsden, he proves that Thomson's “plum pudding” model is incorrect. He proposes a new model of the atom: a massive, positively charged central nucleus, around which electrons orbit. This discovery lays the foundations of modern nuclear physics and redefines our understanding of matter, paving the way for the work of Niels Bohr and, later, for research into nuclear energy and medicine.