A periodic modulation of the amplitude and period of certain RR Lyrae stars, and other related pulsating variables. Blazhko periods range between about 10 days and over 530 days, with a marked peak at 20–40 days. The favoured explanation involves double-mode pulsation, but in certain cases it appears that the star is an oblique rotator. The Blazhko periods may themselves be variable, as in RR Lyrae itself, where a further 4-year cycle seems to occur. The effect is named after the Russian astronomer Sergei Nicolaevitch Blazhko (1870–1956).
Subjects: Astronomy and Astrophysics.