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National Geographic : 1974 Oct
Contents
SOLAR STORMS, known as active regions, can be dissected and analyzed by observing them simultaneously in different wavelengths of ultra violet light. The active regions below, observed on September 11, 1973, are relatively hot areas that emit more intense ultraviolet radiation than their surroundings; they appear here in lighter colors. Each atom radiates light at certain wavelengths that characterize that atom only. When atoms collide with other fast-moving particles at high temperatures, they lose electrons and become ions. As more electrons are torn off, the light from these ions appears in ever-shorter wavelengths, from visible light to ultraviolet and finally X-ray. When light that is characteristic of a particular ion is observed, we know it was emitted from a region where temperature and density favor formation of that ion-and thus we can observe different layers of the sun's atmosphere. In the false-color photo graph at left, the presence of carbon ions, missing two electrons, betrays tempera tures of about 100,0000 F., indicating that this region of the storm occurs near the sun's surface. The active region extends to higher altitudes in the picture at lower left, whose hot spots represent atoms of oxygen stripped of five electrons. Searing gases of two mil lion degrees leap more than 40,000 miles above the sur face (below), as revealed by magnesium atoms missing nine electrons. HARVARDCOLLEGEOBSERVATORY ANDNASA
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