father of O. W. Struve. In 1819 he began to observe double stars, aiming to continue where F. W. Herschel left off. The next year he published the first of many double-star catalogues, the last of which (1852) compared separations and position angles with historical data (his catalogue numbers for doubles are still in use). Struve showed that double and multiple stars are more common than had been suspected. In 1833 Struve moved to Russia to set up the Pulkovo Observatory, near St Petersburg. He made the third reliable measurement of a stellar parallax, that of Vega, in 1840. He also refined values for astronomical constants, including the constant of aberration (see annual aberration).