The collision of two giant clusters of galaxies has been imaged by NASA’s Chandra X-ray Observatory. For the first time, the pressure fronts in this system, which has been compared to a cosmic “weather system,” can be traced in detail. “We can compare this to an intergalactic cold front,” said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. and leader of the international team involved in the analysis of the observations. “A major difference is that in this case, cold means 70 million degrees Celsius.” The gas clouds are in the core of a galaxy cluster known as Abell 2142. The cluster is six million light years across and contains hundreds of galaxies and enough gas to make a thousand more.