German astronomer who established the study of variable stars as an independent branch of astronomy and is renowned for his great catalog listing the positions and magnitudes of 324,188 stars. He studied at the University of Königsberg, Prussia, where he was a pupil and later the successor of Friedrich Wilhelm Bessel. Argelander was appointed director of the Åbo (Turku) Observatory in Finland in 1823 and of the Helsinki Observatory in 1832. In 1837 he published the first major investigation of the Sun's motion through space and in the same year was appointed director of the new observatory in Bonn. In 1844 he began studies of variable stars.

His greatest achievement was the publication of the Bonner Durchmusterung (1859–62), which cataloged stars from the north celestial pole to 2° south of the celestial equator. The result of 25 years' labour, the catalog included all stars down to about the ninth magnitude. This work was reissued in 1950.

Argelander founded the Astronomische Gesellschaft (Astronomical Society), whose object was to expand his work in collaboration with many observatories.