The solar eclipse 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.
Thermochromic ink makes the stamp work. Using the heat of your finger, the image will reveal an underlying image of the moon, which Espenak also took. The image reverts back to the eclipse once it cools.
Thermochromic inks are vulnerable to UV light and should be kept out of direct sunlight as much as possible to preserve this special effect. To help ensure longevity, the Postal Service will be offering a special envelope to hold and protect the stamp pane for a nominal fee.
The back of the stamp will have a map of the eclipse path.