The U.S. Postal Service is anticipating the upcoming total eclipse of the sun with a stamp celebrating the majesty of solar eclipses. This new stamp will be the first U.S. stamp to use thermochromic ink, which reacts to the heat of your touch. When you place your finger over the black disc on the stamp (left), the ink will change from black to clear and reveal an image of the moon (right). The image reverts back to the black disc when it cools. The stamp is a photograph of a total solar eclipse that was seen over Libya in 2006 by astrophysicist Fred Espenak.