02 February 1990
Vol 247, Issue 4942

About The Cover

A photograph of dark sunspots and bright faculae near the sun's limb, obtained in broad-band light with the vacuum tower telescope at Sacramento Peak Observatory. These two kinds of photospheric magnetic structures both influence the total solar irradiance. The smallest facular elements visible are approximately 500 miles in diameter. See page 556. [By permission of the National Solar Observatory/Sacramento Peak, a division of the National Optical Astronomy Observatories, Inc., under cooperative agreement with the National Science Foundation]