A muon-neutrino created in earth's atmosphere has interacted to create a muon in the Super- Kamiokande detector (SK) located 1000 metres under Mt Ikenoyama, Japan. A cylinder of ultra-clean water 41m tall and 39m in diameter, SK is lined with 11200 phototubes to record Cerenkov light produced when charged subatomic particles travel through water faster than light does. Here, coloured dots show tubes that have recorded light. The red end of the spectrum indicates the earliest light to arrive. The muon travelled through the detector from upper left to lower right, producing a clear Cerenkov 'ring' with well-defined edges.