To peer into the Universe's beginnings, scientists study the so-called cosmic microwave radiation (CMB) that was produced just 380,000 years after the big bang. On average, the CMB is a decidedly chilly 2.73 kelvins. In 1992, NASA's Cosmic Background Explorer (COBE) first detected tiny temperature fluctuations, or anisotropy, in the CMB. Nine years later, the Wilkinson Microwave Anisotropy Probe (WMAP) was launched to chart these temperature changes with greater accuracy, sensitivity and resolution. WMAP can resolve temperature differences of only millionths of a degree. Using these new data, a research team led by Charles L. Bennett of the NASA Goddard Space Flight Center and David Spergel of Princeton University compiled a full sky map that reveals our universe in its earliest stages. (The image above shows the map compiled by COBE (top) and the one from WMAP (bottom).) The refinement of the new measurements, comments John Bahcall of the Institute for Advanced Study in Princeton, N.J., represents "a rite of passage of cosmology from speculation to a precision science."
As a result of the information collected by WMAP, the researchers were able to sharpen their estimates of when the first stars formed. The team reports that the lights in our universe came on only 200 million years after the big bang, which is nearly 500 million years earlier than previously thought. "This is a beginning of a new stage in our study of the early universe," Spergel notes. "We can use this portrait not only to predict the properties of the nearby universe, but can also use it to understand the first moments of the big bang."