| Sergey Nikolayevich Blazhko | |
| Native Name: | Серге́й Никола́евич Блажко́ |
| Native Name Lang: | ru |
| Birth Date: | 17 November 1870 |
| Birth Place: | Khotsimsk |
| Death Place: | Moscow, Soviet Union |
| Education: | Moscow State University |
| Occupation: | Astronomer |
| Organization: | Academy of Sciences of the Soviet Union (1929, corresponding member) |
| Known For: | Blazhko crater, planet No. 2445 |
Sergey Nikolayevich Blazhko (ru|Серге́й Никола́евич Блажко́; 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[1] 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.
Crater on the Moon and asteroid No. 2445 are named after Blazhko.[2]