The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. However, in 1868 a method of observing them with a spectroscope at any clear time of day was developed, and in 1930 the invention of the coronagraph allowed them to be continuously photographed. prominences could be viewed extending from the edge of the sun's disk only during a solar eclipse. These are now known to be prominences seen against the bright background of the photosphere. Dark strandlike objects called filaments were discovered on the disk and were originally thought to be a special kind of feature. Eruptive prominences are thin flames of gas often reaching heights of 250,000 mi (400,000 km) they occur most frequently in the zones containing sunspots. Quiescent prominences bulge out from the surface about 20,000 mi (32,000 km) and can last days or weeks. Two major classifications are the quiescent and the eruptive prominences. Most spectacular of the solar features are the streams of hot gas, called prominences, that shoot out thousands or even hundreds of thousands of miles from the sun's surface at velocities as great as 250 mi per sec (400 km per sec). The elements of each layer are sometimes distributed in bright, cloudlike patches called plages, or flocculi, and in general are located along the same zones as sunspots and fluctuate with the same 11-yr cycle the relationship between the two is not yet understood. Other types of solar activity are found to occur in the chromosphere. Any point on the sun will erupt a spicule about once every 24 hr and there may be up to 250,000 of them at any instant. The spicules, each about 500 mi (800 km) in diameter, shoot out at 20 mi per sec (32 km per sec) and rise as high as 10,000 mi (16,000 km) before falling back. Solar Activity Originating in the Chromosphere Spicules and PlagesĪt 600 mi (1,000 km) above the photosphere, the chromosphere separates into cool, high-density columns, called spicules, and hot, low-density material. The chromosphere consists of three distinct layers that, moving outward from the sun's surface, decrease in density and increase abruptly in temperature. ![]() 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. An analysis of the emission lines gives information about the heights of the chromosphere and the heights at which various elements exist in it. 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. The flash spectrum has been a valuable tool in the study of the chromosphere.
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