corona

The structure of the Sun. Nuclear reactions at the core release vast amounts of energy in the form of light and heat that radiate out to the photosphere and corona. Surges of glowing gas rise as prominences from the surface of the Sun and cooler areas, known as sunspots, appear as dark patches on the star's surface.

Faint halo of hot (about 2,000,000°C/3,600,000°F) and tenuous gas around the Sun, which boils from the surface. It is visible at solar eclipses or through a coronagraph, an instrument that blocks light from the Sun's brilliant disc. Gas flows away from the corona to form the solar wind. It is not certain why the corona is so much hotter than the surface of the Sun (about 6,700°C/12,100°F). The heating may be due to interactions with the Sun's magnetic field, or to pulses of sound waves from the Sun. NASA's Reuven Ramaty High-Energy Solar Spectroscopic Imager mission, launched in 2001, studies the evolution of energy in the corona.

Corona

City in Riverside County, southwestern California, USA, on the northeast of the Santa Ana Mountains, 66 km/42 mi east-southeast of Los Angeles and 14 km/9 mi southwest of Riverside; population (1990) 76,100. Industries include quarrying, glass and ceramics. Orchard equipment, citrus juices, and wood items are produced, and Corona is a packing and shipping centre for regional citrus fruits.

Founded in the late 19th century, Corona thrived on deposits of clay, sand, and gravel. Noted for its circular Grand Boulevard, the city doubled in population as a residential suburb in the 1980s.

The Cleveland National Forest lies to the southwest.