National Geographic : 1965 Nov
Three ways to see the sun THE FACE of the sun wears many expressions. Photographed in white light (right, top) through a solar telescope, it shows sunspots in the form of dark flecks. Viewed the same day in the violet light of radiant calcium ions, filtered by a spectroheliograph, the sun appears blotchy (center). Massive calcium clouds called plages hover over the sunspot areas visible in the top photograph, as well as over other sunspots that are waning or just beginning to form. Mirrored in a magnetogram taken at a different time, the sun's magnetic face (bottom) shows that the sun is a relatively weak magnet. Shades of gray indicate low intensity, white areas are stronger, and heavy black blots mark small regions of intense activity. These blots often coincide with sunspots, which may measure thousands of times the magnetic intensity of the sun as a whole. Sunspot movements prove that the sun rotates, as does the earth. This 1947 outbreak, largest sunspot group on record, covered seven billion square miles. Lacking rigidity, different parts of the sun spin at various speeds. Scientists believe that turbulence thus generated forces giant twisting loops of electrified gas to break through the surface, forming the sunspots. U. S. NAVALOBSERVATORY(RIGHT, UPPER); McMATH HULBERTOBSERVATORY(CENTER); MT. WILSON AND PALOMAROBSERVATORIES© N.G .S.