Inside the Sun

The outer third of the solar interior, where energy is carried by convection — hot plasma rises, cools, and sinks, like a pot of boiling water. This churning is visible at the surface as granulation and drives the magnetic activity of the Sun. It sits above the tachocline and below the photosphere.

The layer surrounding the core, from about a quarter to seven-tenths of the solar radius, where energy travels outward as radiation. Photons are absorbed and re-emitted so many times that a single packet of energy can take on the order of a hundred thousand years to cross it. The plasma here rotates almost as a rigid body.

The innermost region of the Sun, out to about a quarter of its radius, where nuclear fusion powers the star. At roughly 15 million kelvin and immense density, hydrogen fuses to helium mainly through the proton–proton chain, releasing the energy that slowly works its way outward. Almost all of the Sun's luminosity is generated here.

The thin shear layer near seven-tenths of the solar radius, where the rigidly rotating radiative interior meets the differentially rotating convection zone. This velocity shear is widely thought to be where the Sun's large-scale magnetic field is generated — the seat of the solar dynamo.