Solar neutrino. A neutrino from the sun produces a ring of light in the Super-Kamiokande detector located 1000 metres under Mt Ikenoyama, Japan. A cylinder of ultra-pure water 41m tall and 39m in diameter, 'Super-K' is lined with 11200 phototubes to record Cerenkov light produced when charged subatomic particles travel through water faster than light does. In this electronic display, coloured dots show tubes that have recorded light when the solar neutrino set an electron in the water into motion. The electron emits a cone of Cerenkov radiation that forms a ring on the wall of the detector.