From AMS Glossary
The layer of solar atmosphere above the photosphere and beneath the corona. It is a relatively thin solar layer (generally 2500–3000 km in depth) of predominantly hydrogen and helium gases. Various chromospheric phenomena can extend even higher (e.g., spicules up to 10 000 km) into the corona. The chromosphere is the source of the strongest lines in the solar spectrum, including the Balmer alpha line of hydrogen (H-alpha), and the source of the red color often seen around the rim of the moon during a total solar eclipse.
Term edited 13 August 2018.