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Few people have ever claimed to see three rainbows arcing through the sky at once. In fact, scientific reports of these phenomena, called tertiary rainbows, were so rare—only five in 250 years—that until now many scientists believed sightings were as fanciful as Leprechaun's gold at a rainbow's end.

Special Issue: Cities The city is a solution to the problems of our age, and this week, we present it in the true urban spirit: best ideas forward

Special Issue: Cities The city is a solution to the problems of our age, and this week, we present it in the true urban spirit: best ideas forward

In this month's special issue of Physics World, which examines the science and applications of invisibility, Martin McCall and Paul Kinsler of Imperial College London describe a new type of invisibility cloak that does not just hide objects – but events.