Number 194 (Story #4), September 13, 1994 by Phillip F. Schewe and Ben Stein THE TEMPERATURE OF THE COSMIC MICROWAVE BACKGROUND (CMB) , a uniform 2.7 K (not counting tiny fluctuations at the mK level) across the sky, is in effect the ambient temperature of the universe. According to the big bang model, this temperature would have been higher in the past; in fact, it should increase linearly with redshift as we look farther back in time. Using the Keck Telescope, astronomers have indirectly measured the CMB temperature at a redshift of 1.776 by looking at the fine features in the absorption spectrum of carbon atoms in an interstellar cloud sitting in front of a more distant quasar. The measured CMB temperature, 7.4 K, is very close to the big bang prediction of 7.6 K. (A. Songalia et al., Nature, 1 Sept.)