Malcolm Sim Longair (born 1941), British astronomer and physicist. Longair is currently (2007) Jacksonian Professor of Natural Philosophy at the University of Cambridge. His work has been primarily in high-energy astrophysics and cosmology. He has also worked to popularise science, delivering several public lectures on astronomy and astrophysics. He was Astronomer Royal for Scotland (and thus also Regius Professor of Astronomy at the University of Edinburgh), from 1980 to 1990, and also President of the Royal Astronomical Society (1996-1998). He was made CBE in 2000.