The sun is a magnetically active star. Its activity manifests itself as dark sunspots and bright faculae on its visible surface, as well as violent mass ejections and the acceleration of high-energy particles resulting from the release of magnetic energy in its outer atmosphere.
The frequency with which these phenomena occur varies in a somewhat irregular activity cycle of about 11 years, during which the global magnetic field of the Sun reverses.
The solar magnetic field and the activity cycle originate in a self-excited dynamo mechanism based upon convective flows and rotation in the outer third of the solar radius.
Analysis of radioactive isotopes in tree rings and in polar ice sheets show that other such grand minima of solar activity have occurred over the past millennium, and also revealed a number of quasi-periods in the activity variations, ranging from 80 to about 2,000 years.
Before the magnetic nature of sunspots and other phenomena were discovered, a popular theory associated the activity cycle with the planetary orbital periods, primarily motivated by the similarity between the approximately 11-yr solar cycle and the 11.87 orbital period of Jupiter.
R. Cameron and M. Schussler compared the quasi-periods found in this data set between 40 and 600 years with periods in the tidal torque exerted on a thin shell in the solar interior, which they assumed to be ellipsoidally deformed. Abreu et al. found seemingly striking similarities between the solar and the planetary periods in 5 period bands.
Their statistical analysis appeared to show that these coincidences are not due to chance, which would mean that the planets affect solar activity after all.
The findings have been published in Astronomers and Astrophysics.
--ANI (Posted on 06-09-2013)