Sergey Nikolayevich Blazhko (November 17, 1870, Khotsimsk – February 11, 1956, Moscow) was a Russian and Soviet astronomer, a corresponding member of the Academy of Sciences of the Soviet Union (1929). He was a graduate of Moscow State 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.

Awards and honours

Crater on the Moon and asteroid No. 2445 are named after Blazhko.