Fredrik Carl Mülertz Størmer (3 September 1874 – 13 August 1957) was a Norwegian mathematician and astrophysicist.
In mathematics, he is known for his work in number theory, including the calculation of p and Størmer's theorem on consecutive smooth numbers.
In physics, he is known for studying the movement of charged particles in the magnetosphere and the formation of aurorae, and for his book on these subjects, From the Depths of Space to the Heart of the Atom.
He worked for many years as a professor of mathematics at the University of Oslo in Norway.
A crater on the far side of the moon is named after him.