7 - Stellar activity and activity cycles

Summary

Scintillate, scintillate, globule vivivic

Fain would I fathom thy nature specific.

Variation on a well-known theme

The solar-stellar connection

Hale's conviction that solar physics is an essential component of astrophysics was shared by some, but unfortunately not by all, astrophysicists. Nevertheless, a further important initiative in this spirit was taken at Mount Wilson in 1966, when, using the 100-inch Hooker telescope, Olin Wilson and his colleagues began a long-term study of 91 cool dwarf stars (Wilson 1978). In 1978 this project (the ‘HK Project’) was transferred to the Mount Wilson 60-inch telescope, which was dedicated entirely to the continuation and extension of this work and has become identified with a particular methodology known as the solar-stellar connection.

Although the Sun permits the detailed two-dimensional study of its activity phenomena, it exhibits only a single set of stellar parameters, since its mass, size, composition, and state of evolution are necessarily fixed at this point of time. On the other hand, stars, as observed from earth, are essentially one-dimensional objects, but they offer a wide range of physical parameters which permit a more thorough testing of theories and conjectures regarding common phenomena than is possible for the Sun alone. The solar-stellar connection aims to bring these two lines of investigation together in order to further our understanding of the properties of the Sun and other late-type stars.

Even before the solar-stellar connection methodology became recognized as such, there were many examples of the successful application of solar results to stellar investigations.