When the shadow of the moon swept across Europe, the Middle East and India last August 11th, for a few minutes millions of people were able to gaze up in the sky and observe the surface of the sun while it was in a state of high excitement.
Figure 1. Imagery from the Solar and Heliospheric Observatory (SOHO) spacecraft captures solar prominences of every shape and size. A "pseudo-flame" coloration of monochromatic images taken at 304 angstroms' wavelength (in the extreme ultraviolet, at a spectral resonance line of singly ionized helium) dramatizes the glow of material at temperatures between 60,000 and 80,000 kelvins. Although some of the prominences visible in this set are relatively modest in size, others, such as one seen on September 14, 1999 (upper right), are enormous. Reaching hundreds of thousands of kilometers outward, the span of this gargantuan arch is about as large as the separation between the Earth and the Moon. And whereas some of the prominences shown form uncomplicated loops, others are obviously twisted. As the author explains, such helical structures reveal the presence of huge electric currents flowing within the hot gas. He bases this conclusion, in part, on the results of his experiments with small-scale analogues of solar prominences. These miniature prominences are about a billion times smaller than the structures seen above, and they evolve about a billion times faster. But because they are governed by the same equations, inferences about the sun can be drawn from them.
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