Growing up, my uncle had this collection of glasses that had sexy women on them. When you put cold liquids into them, the clothes disappeared on the glasses leaving the ladies in their undies. I thought those were the greatest glasses ever made. ThinkGeek has something sort of the same, but with much less naked, and much more astronomy.
The Constellation Heat Change mug has landed, and it’s designed to show you Cassiopeia, Cepheus, Cygnus, Hercules, Leo, Lynx, Lyra, Orion, the Big Dipper, and the Little Dipper when hot liquids are added. When in its default state, the mug has no lines on it to connect the stars into constellations.
As soon as you add that hot beverage to the mug, the lines show up and you can find constellations on the side of the mug. No lines means your coffee is too cold. The mug is hand wash only and is available for $11.99 (USD).