The chromosphere is the layer of the Sun's atmosphere outside
the photosphere and inside the solar transition region.
It is a few thousand 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,
with a dip down to 3800 K between.
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.