Duncan MacLaren Young Sommerville FRSE FRAS (1879–1934) was a Scottish mathematician and astronomer. He compiled a bibliography on non-Euclidean geometry and also wrote a leading textbook in that field. He also wrote Introduction to the Geometry of N Dimensions, advancing the study of polytopes. He was a co-founder and the first secretary of the New Zealand Astronomical Society. Sommerville was also an accomplished watercolourist, producing a series New Zealand landscapes.