Magnetic activity cycles in the chromospherically active secondary component induce changes in its radius of gyration that have been linked to recurrent orbital period variations on the order of ≈ 10−5 via the Applegate mechanism [REF].
Algol is about 92.8 light years from the Sun, but about 7.3 million years ago it passed within 9.8 light years of the Solar System[REF] and its apparent magnitude was about −2.5, which is considerably brighter than the star Sirius is today.