Stars are the most visible components of the Universe. Most of what we know of the universe comes from studying stars. Variability of Stars provides powerful access to their structure, environment and evolution. Stars are crucial elements for understanding the history and evolution of our Universe, of galaxies, of our local solar system, and Stars most probably host zillions of planets.

Stars represent laboratory sites for physical processes that cannot be tested experimentally on Earth. They are crucial for understanding basic physics, such as nuclear physics, particle physics, statistical physics, hydrodynamics, atomic physics and opacities, and more. We are facing the limitations in theoretician’s modelling of the basic radiation, plasma and other physics, which oversimplify (or ignore) the treatment of radiation–matter coupling, magnetic fields, dynamical processes, etc. 

Observing Stars from satellites has significantly increased the data volume and parameter space for a realistic modelling of these objects. Variability can now be traced down to incredibly low noise levels allowing to uncover new populations of stars and reveal limits in our physical understanding of their structure and evolution. In particular, BRITE-Constellation has demonstrated the unique advantage of nano-satellites for exploring stars which are bright (and close) enough to allow access to other fundamental techniques, like interferometry, high accurate parallaxes, direct imaging, very high spectral and temporal resolution, etc.