The United States Postal Service is releasing a new stamp today that uses thermochromic ink to give us two different images on one stamp. The eclipse stamp is a commemoration of the total solar eclipse that will cross the U.S. on August 21.
The stamp image is a photograph taken by astrophysicist Fred Espenak, aka Mr. Eclipse, of Portal, AZ, that shows a total solar eclipse seen from Jalu, Libya, on March 29, 2006.
In the first U.S. stamp application of thermochromic ink, the Total Eclipse of the Sun Forever stamps will reveal a second image. Using the body heat of your thumb or fingers and rubbing the eclipse image will reveal an underlying image of the Moon (Espenak also took the photograph of the Full Moon). The image reverts back to the eclipse once it cools.
Stamp collectors (and people who take months to use a sheet of stamps) are warned to store the stamps away from sunlight to preserve the effect. You can buy a special envelope for them. The First-Day-of-Issue ceremony will be at the University of Wyoming library in Laramie today, during a summer solstice event. The eclipse stamps should roll out to post offices across the country soon. -via Metafilter