chro·mo·sphere / ˈkrōməˌsfi(ə)r/ • n. Astron. a reddish gaseous layer immediately above the photosphere of the sun or another star. Together with the corona, it constitutes the star's outer atmosphere.DERIVATIVES: chro·mo·spher·ic / ˌkrōməˈsfi(ə)rik; -ˈsferik/ adj.

chromosphere Layer of the Sun's atmosphere between the photosphere and the corona. It is c.10,000km (6000mi) thick and is briefly visible near the beginning and end of a total solar eclipse as a spiky red rim around the Moon's disk. At its base the temperature of the chromosphere is c.4000K, rising to 100,000K at the top.