The chromosphere is a region in the atmosphere of a star between the photosphere and the corona.
The solar chromosphere has a characteristic red colour due to certain lines in the hydrogen spectrum (the H-alpha line). It is a layer about 10,000 km thick of which the temperature increases from 4500 K to 500,000 K.
It was discovered and observed during eclipses of the Sun, it was studied photographically using filters, and later using coronographs and spectroheliographs.
Spicules formed in the photosphere pass through the chromosphere.
The solar prominences that originate there were studied by Lockyer as early as 1868. These thin structures are composed of relatively cool gas (7000° K) projected into the solar atmosphere in the form of filaments that can extend up to 400,000 km from the surface of the Sun. They are easy to observe during eclipses. They appear dark on the disk of the Sun and bright outside the disk. There are active prominences (associated with a centre of activity), quiescent ones and eruptive ones.
Eruptive prominences are a sudden eruption of energy from the Sun's disk. They last from between several minutes and a few hours during which time radiation and particles are emitted.