(krō'mӘsfēr´´) [Gr.,=color sphere], layer of rarefied, transparent gases in the solar atmosphere; it measures 6,000 mi (9,700 km) in thickness and lies between the photosphere (the sun's visible surface) and the corona (its outer atmosphere). The flash spectrum has been a valuable tool in the study of the chromosphere. This spectrum is obtained before a solar eclipse reaches totality and is formed from the thin arc of the sun disappearing behind the moon's disk. An analysis of the emission lines gives information about the heights of the chromosphere and the heights at which various elements exist in it. Using the flash spectrum, scientists have found that the chromosphere is composed primarily of hydrogen, which causes its visible pinkish tint, and of sodium, magnesium, helium, calcium, and iron in lesser amounts. The chromosphere consists of three distinct layers that, moving outward from the sun's surface, decrease in density and increase abruptly in temperature. The lower…