A cut-away view of the Sun.
Gas movements within the convective envelope.
A convective envelope is a region inside a star where energy is transported mainly by convection. In the Sun, the convective envelope begins just below the photosphere and extends down for about 180,000km (about a fifth of a solar radius); it accounts for about 2/3 of the Sun's volume but only about 1/60 of the Sun's mass. The temperature inside this layer is thought to vary between 2 million and 6,500K, and the density between 100 times more and 4,000 times less than that of air at Earth's surface.
In stars less massive than the Sun, the convective envelope extends down to comparatively much greater depths, and in stars of less than 0.4 solar mass energy transport is entirely convective. In high mass stars, however, the convective envelope is much smaller or is entirely replaced by a radiative envelope.