Sergey Nikolaevich Blazhko (Сергей Николаевич Блажко in Russian) (November 5(17), 1870 - February 11, 1956, Moscow) was a Russian and Soviet astronomer, a corresponding member of the Soviet Academy of Sciences (1929). He was a graduate of Moscow University and held a number of positions there including head of the Moscow Observatory from 1920-1931. He discovered a secondary variation of the amplitude and period of some RR Lyrae stars and related pulsating variables, now known as the Blazhko effect.
- Hockey, Thomas (2009). The Biographical Encyclopedia of Astronomers. Springer Publishing. ISBN 978-0-387-31022-0. Retrieved August 22, 2012.
- Kulikovsky, P.G. (1970–80). "Blazhko, Sergei Nikolaevich". Dictionary of Scientific Biography. 2. New York: Charles Scribner's Sons. pp. 195–197. ISBN 978-0-684-10114-9.