It's not hard to find a heat-changing mug that displays an impressive picture, but this design really reaches for the sky. ThinkGeek offers a $15 mug that reveals the aurora borealis, the astronomical event often called the northern lights. When empty, the outside of the ceramic cup shows a blank night sky—but add a little coffee, and the mug brightens right up. The heat from your beverage causes a stream of vibrant green colors to appear along the container's side.
ThinkGeek explains their inspiration on their website:
Much as caffeine particles pass into our bloodstream and make us bounce off walls, so, too, the particles from solar winds pass through the Earth's magnetosphere near the poles and share energy, causing a spectacular display in the upper atmosphere. When these particles collide with oxygen in particular at lower altitudes (up to 150 miles), the photon released appears green or yellow, giving a similar light show as to the one captured on this mug when you fill it with warm liquid.
For more heat-sensitive kitchenware, also check out this Pac-Man pint glass that comes to life with a cold drink.