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An electron-neutrino created in earth's amtosphere has interacted to create a electron 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 electron produces a fuzzy 'ring' due to radiation of subsidiary photons that turn into electron-positron pairs. (KEYSTONE/SCIENCE PHOTO LIBRARY/TOMASZ BARSZCZAK/SUPER-KAMIOKANDE COLLABORATION)