The chromosphere is the layer (approximately 4,000 kilometers deep) immediately outside the photosphere (from the Greek chroma meaning color, a reference to its pinkish appearance due to its primary emission at the red hydrogen wavelength, the Hα line). This region is seen during solar eclipses when light from the brighter photosphere is blocked from view. This region is also known as the reversing layer because it is the source of most of the absorption lines seen in the spectrum (whereas the primary process in the underlying photosphere is emission of light). At its base, the temperature is 4,500 K, but at its top, the temperature is 10,000 K, a reversal of the trend for temperature to decrease from the center of the Sun up through the photosphere (see Figure ). Shock waves moving faster than the speed of sound, generated by the convective turbulence in the photosphere, move into the thinner chromosphere, heating its material. Features associated with the chromosphere are the spicules, narrow jet‐like fountains rising higher into the solar atmosphere. They are perhaps associated with the granules of the photosphere.
Figure 1
Temperature in the photosphere and chromosphere.