A RUDIMENTARY MUON MAP OF THE SKY has been carried out by the Soudan-2 detector, located deep in a Minnesota mine and built originally to look for proton decay. To be exact, Soudan records muons produced by incoming cosmic rays hitting the atmosphere. The muon imaging process clearly senses the shadow cast by the passing Moon, which temporarily blocks cosmic rays coming from that position in the sky. (Science, 18 June.)