Giant Convection Cells: Unlike the Sun's millions of tiny granules, Betelgeuse has only ~5-10 massive convective cells covering the disk. These cells are responsible for its dramatic surface asymmetry.
Pulsation: Semi-regular with ~420 day and ~185 day periods. Radius changes by ~15%, driving TiO molecular absorption variations that make it appear to dim and brighten (Δmag ~1).
Great Dimming (2019–2020): A dust ejection event caused Betelgeuse to fade to its dimmest level in modern records. A large convective plume ejected material that condensed into dust south of the star.
Molecular shell: TiO, AlO, and SiO form in the cool extended atmosphere, creating additional opacity layers beyond the photosphere.