This stamp is very unique in that it reacts to the temperature. When heated by touch, an image of the Moon appears in the middle. The image below shows the stamp in two states. The left image shows the normal stamp. The right image shows the same stamp after being warmed by your hand. This process uses Thermochromatic ink, the first of its kind by the USA postal service.
Because thermochromatic ink reacts to UV light you should keep the stamps out of direct sunlight (somewhat ironic given the subject matter of the stamp). From USPS announcement:
"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 stamp images come from Fred Espenak (Mr Eclipse). He supplied both images (eclipse and Moon).
Stamp sales are expected to be brisk. Local post offices may run out of them quickly so if you plan to send post cards or letters with the stamp on them (or just add a few to a collection of eclipse stamps) you need to move quick to get some. As the eclipse date approaches the stamps may be difficult to obtain.
These stamps are a rare honor to both the eclipse taking place across the continental USA and the Fred Espenak who has provided many years of eclipse details to us all. Lobbying by eclipse chasers led to this special commemorative and Fred worked in secret (he didn't tell any of us!) with the postal service to deliver this cool (err, hot?) product. Thanks to all involved, this is a unique and special way to commemorate a very unique and special eclipse.
To see other eclipse stamps from the past visit the virtual stamp collection gallery at www.eclipse-chasers.com