Roemer, Olaus Christensen

Born Sept. 25, 1644, in Aarhaus; died Sept. 19, 1710, in Copenhagen. Danish astronomer. Professor at the University of Copenhagen (from 1681).

In 1675, Roemer determined the speed of light from observations of occultations of the satellites of Jupiter. He also invented several astronomical instruments, including the meridian circle and the equatorial telescope with an hour circle and a declination circle. With these instruments, he determined the declination and right ascension of more than 1,000 stars.