Chromosphere

A chromosphere ("sphere of color", from the Ancient Greek words χρῶμα (khrôma) 'color' and σφαῖρα (sphaîra) 'sphere') is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona.

The name was suggested by the English astronomer Norman Lockyer after conducting systematic solar observations in order to distinguish the layer from the white-light emitting photosphere.

Narrow jets of plasma, called spicules, rise from this homogeneous region and through the chromosphere, extending up to 10,000 km (6,200 mi) into the corona above.

The chromosphere has a characteristic red color due to electromagnetic emissions in the Hα spectral line.

They are different from solar prominences because they are concentric arches with maximum temperature of the order 0.1 MK (too low to be considered coronal features).

These cool-temperature loops show an intense variability: they appear and disappear in some UV lines in a time less than an hour, or they rapidly expand in 10–20 minutes.

Images taken in typical chromospheric lines show the presence of brighter cells, usually referred to as the network, while the surrounding darker regions are named internetwork.

An illustration of the structure of the Sun
When observed in the H α spectral line, the chromosphere appears deep red.
The red color of the chromosphere could be seen during the solar eclipse of August 11, 1999 .
High-resolution observations of the solar chromosphere show hair-like spicules, here shown in a false colored image made in borderline ultraviolet radiation of calcium K-line.