Earth’s atmosphere, here in light blue, acts like the window on a glass greenhouse. Some gases — such as CO2 — trap certain wavelengths of light (here shown in red). That trapped energy, or heat, warms our planet.
At a wearer’s command, an electric current can switch these sunglasses from dark to clear in about a second.
This explosion was ready for its close-up. Chemists used a high-speed camera to figure out why metals explode when they come in contact with water.