The chromosphere is the layer of the Sun's atmosphere outside the photosphere and inside the solar transition region. It is about 2000 kilometers deep and its density is a hundred millionth that of the Earth's atmosphere. The inner boundary is 6000 K and the outer boundary is 35000 K. The chromosphere is visible during a solar eclipse.
The term plage is used for certain kinds of bright regions of the chromosphere. They occur near sunspots.