Øystein Elgarøy (13 June 1929 – 8 September 1998) was a Norwegian astronomer, with a specialty in solar radio astronomy.
He was appointed as a lecturer of astrophysics at the University of Oslo, located in Oslo, Norway, in 1968, and was a professor from 1983. Elgarøy published several books, including textbooks.
He was a brother of composer Jan Elgarøy. He was a strong apologist for Christianity until he became an atheist.
His son, also named Øystein Elgarøy (born 1972), is a professor of astrophysics at the University of Oslo.