The mystery of some atmospheric halos remains unexplained after 5,000 years
For the first time in nearly 5,000 years of observation, researchers have fully cataloged the optical illusion created in the sky when light shines through ice crystals known as atmospheric halos. The detailed ‘inventory’ of atmospheric halos often looks at atmospheric optical illusions from known sources and explains rarer halos, including those whose origins remain a mystery. Halos are caused by the accumulation of water ice crystals smaller than 10 micrometers in the atmosphere. The qualities of these atmospheric illusions, such as their color or whether they have white arcs, spots or rings, are determined by the shape and orientation of the ice scattering from and the path that light takes towards these crystals. Often, the type of crystal behind the scattering can be identified by the shape of the halo they create. Related: What makes Earth’s atmosphere so special? This atmospheric illusion has been documented by mankind since at least the Babylonian era — which began around 189