To celebrate the upcoming total solar eclipse, the U.S. Postal Service is releasing its first thermochromic stamp.
The stamp reacts to heat. Touching it reveals an image of the moon, and as it cools, it turns back to black.
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The back of the stamp shows the path of the eclipse across the continental U.S.
It mimics what we can expect to see during the celestial event. As the moon passes in front of the sun, it should cast a shadow about 70 miles wide.
The last time a total solar eclipse swept across the U.S. from coast to coast was almost 100 years ago.
