Publicly available chapter of the book written by Alexander I. Shapiro, Hardi Peter and Sami K. Solanki
Our Sun is a special star - not only for the reason that it is vital for us and life on Earth, but even in comparison to other stars, which are of similar size, luminosity, and magnetic properties. The Sun’s radiative emission varies on many different time-scales, ranging from a fraction of a second to centuries. Variations on time-scale longer than a day are linked to magnetic fields, where the solar magnetic cycle is of nearly 11-years. Investigations of the past years show that the Sun’s brightness variations following an eleven year cycle are markedly weaker than those of most comparable stars. This research group, "Connecting Solar and stellar Variables", searches of the reason of this difference by looking at a link between the Sun and stars. Why do these bodies behave so similarly and yet so differently? And can findings from solar research be transferred to distant stars?
Traditionally, solar and stellar research are rather separate disciplines. One of the reasons is the completely different accessibility of their research objects: While numerous satellites orbiting Earth and space probes observe the Sun from close up and supply a wealth of different measurement data, information about other stars has to be excerpted from light that has traveled many trillion kilometers to reach Earth. In recent years, however, the situation has changed. One of the driving forces behind this development was the discovery of stellar brightness fluctuations following their activity cycles – and thus very akin to the Sun’s eleven-year cycle. These stellar variations have proven to be much stronger than those of the Sun. Possibly, this also holds true for variations on shorter time scales. Thanks to the CoRoT and Kepler space telescopes provided by the French and European space agencies, exact measurements from a large number of stars are now available with an unprecedented level of accuracy. The planned missions TESS and PLATO will further improve the data situation.