Early in 1996, scientists working at the CERN accelerator laboratory in Geneva, Switzerland, reported seeing 11 electrical signals that seemed to come from antihydrogen atoms, and estimated that two of these were noise. Even though most physicists were quite certain that antihydrogen could be formed, this report generated great interest because for the first time an antimatter atom had been directly observed. The antihydrogen atom is the antimatter counterpart of the simplest atom, the hydrogen atom. Within the hydrogen atom, a single electron orbits a single proton. Within the antihydrogen atom, the electron and proton are replaced by their antiparticle counterparts, the positron and antiproton. A single positron thus orbits a single antiproton.