The Structure of the Sun: The Crhomosphere
Above the photosphere the temperature drops to a minimum of about 4,500 K, and then, remarkably enough, begins to rise. During a few seconds around totality during a solar eclipse, a thin ring (annulus) about 10,000 km (6,200 mi) thick around the limb is seen shining with a reddish glow, leading to its designation as the chromosphere ("color sphere"). Upon examination with a telescope and spectrograph at high resolution, most of the chromospheric emission is seen to come from very fine jets of outward-moving gas called spicules, at a temperature of about 15,000 K and a density of some 1011 particles/cm3. A spicule lasts some 5 to 10 minutes and is typically 6,000 km (3,700 mi) high and perhaps one-tenth as thick. The gases are moving outward at speeds of about 10 km/sec (22,000 mph).