Celebrating the coast-to-coast total solar eclipse next month, the USPS has released a commemorative stamp featuring thermochromic ink. When cool, the stamps show the eclipsed sun (below); when heat is applied, they show the moon (above!) They are beautiful in person, and I highly recommend picking some up (go for the folio. I admit, the framed art is pretty tempting!)
On August 21, 2017, tens of millions of people in the United States will have an opportunity to view a total eclipse of the Sun. A total solar eclipse was last seen on the U.S. mainland in 1979, but only in the Northwest. The eclipse this summer will sweep a narrow path across the entire country—the first time this has happened since 1918. The U.S. Postal Service® anticipates this rare event with a stamp celebrating the majesty of solar eclipses.
The Total Eclipse of the Sun stamp is the first U.S. stamp to use thermochromic ink, which reacts to the heat of your touch. Placing your finger over the black disc on the stamp causes the ink to change from black to clear to reveal an underlying image of the moon. The image reverts back to the black disc once it cools. The back of the stamp pane shows a map of the eclipse path. The stamp uses a photograph taken by astrophysicist Fred Espenak of a total solar eclipse that was seen over Jalu, Libya, on March 29, 2006. Mr. Espenak also took the photograph of the full moon that is revealed by pressing upon the stamp image. The reverse side of the stamp pane shows the path across the United States of the forthcoming August 21, 2017, total solar eclipse and gives the times that it will appear in some locations.