Nils Mustelin (11 August 1931 in Turku – 28 April 2004 in Helsinki) was a Finnish professor of physics, noted astronomer, and popular skeptic.
Mustelin was born in Turku, where he also spent his school years and studies. He matriculated in 1949 and studied physics at Åbo Akademi, graduating as a Ph.D. in 1963. He has worked at many places, including the University of Helsinki, Nordforsk, Tekes, and COST. After retiring he was a member of the board at the City of Helsinki, representing the Swedish People's Party.
Mustelin is known for his many scientific books, primarily his astronomic book Elämää maailmankaikkeudessa? ("Life in the universe?"). He is also famous for inventing sporalogy, a humorous pseudoscience parodying astrology. He was the chairman of Skepsis ry (the Finnish association of skeptics) in 1989-1992.
Nils Mustelin was an expert in Classical Music, often appearing on TV and Radio in various panels and competitions.