The Observatory of Leiden University was founded in 1633, but it was Frederik Kaiser (1808-1872) who laid the foundations for the institute in its modern incarnation. He came to Leiden in the 1820s, and in 1860 founded the new Observatory next to the botanical gardens in Leiden.

Kaiser’s main research program was fundamental astrometry (precision measurement of star positions), using a meridian circle. He had few students. His successor Hendrikus van de Sande Bakhuyzen continued his work. Both Kaiser and Bakhuyzen were also active in geodesy (measuring the earth). Bakhuyzen was succeeded by his younger brother Ernst. By that time, the Observatory was in decline.

In 1918, Willem de Sitter succeeded the younger Bakhuyzen as director of the Observatory. He had already been professor of astronomy since 1908. Together with professor and deputy professor Ejnar Hertzsprung, he started a reorganisation, expanding the institute and introducing new research and education programmes. In 1924 they contracted young Jan Oort. Over the following decades, the Observatory became a prominent astronomical institute with a renowned education programme.

After the Second World War, the Observatory expanded further. Especially radio astronomy became an important subject. In 1974, the institute moved to a new location elsewhere in Leiden.