The sun and its atmosphere consist of several zones or layers. From the inside out, the solar interior is composed of the core, the radiative zone, and the convection zone. The solar atmosphere consists of the photosphere, the chromosphere, a transition region, and the corona. Beyond the corona is the solar wind, which is actually an outward flow of coronal gas. The sun's magnetic fields rise through the convection zone and erupt through the photosphere into the chromosphere and corona. The eruptions lead to solar activity, which includes such phenomena as sunspots, flares, prominences, and coronal mass ejections.