Layer of the Sun's atmosphere, several thousand miles thick, above the photosphere and below the corona. The chromosphere (literally colour sphere) is briefly visible as a thin ring, red from hydrogen's emission spectrum, during solar eclipses when the photosphere is obscured by the Moon. At other times it can be observed only with special instruments. Its temperatures range from about 7,000 °F (4,000 °C) about 700 mi (1,100 km) above the photosphere, increasing with altitude to several hundred thousand degrees. Solar flares and solar prominences are mainly chromospheric phenomena.