Number 160 (Story #4), January 14, 1994 by Phillip F. Schewe and Ben Stein THE SOLAR CHROMOSPHERE IS COLDER than we thought. The chromosphere is the region between the photosphere (the sun's surface, at a temperature of about 6000 K) and the corona (whose temperature is 1 million K or more). Previously scientists had figured that the chromosphere temperature was relatively cool---an estimated 4300 K at an altitude of 500 km above the sun's surface---but new measurements made at Kitt Peak show that the chromosphere is colder than this. High-resolution infrared observations of carbon monoxide molecules at the limb of the sun provide a new minimum temperature of 3500 K which, furthermore, seems to occur at a higher altitude, 1100 km. Robert Noyes of Harvard Smithsonian says that carbon monoxide clouds may be a transitory phenomenon in the solar atmosphere. (Science, 7 Jan. 1994, Science News, 8 Jan.)