But new evidence showed that shock waves did not have enough energy to actually heat the corona. We do not actually know how the corona is heated. It probably comes from the solar magnetic or electric fields. Bumps on the sun are called granules. They are the opposite of sunspots.
Sunspots are lower on the surface while the granules are higher.
They last only a few minutes and then are replaced by another one just like waves in the ocean. They are the size of an Earth continent. Granules are created by convection. They are about a hundred kilometers across. Their volume of gas is rising from and falling a shell of convection otherwise known as the convection zone located under the photosphere.