The astronomer Olbers (who always kept a ‘day job’ in medicine, and is sometimes known as Heinrich Wilhelm Olbers) and the great mathematician and astronomer Gauss were regular correspondents. Encke told him (and Bessel and Gauss) when he made his momentous discovery of comets with short orbital periods. Struck by the self-taught Bessel’s prodigious talents, Olbers persuaded him to drop the security of his apprenticeship in commerce, and become an astronomer instead.