There’s a celestial trick to the latest postal stamp

CAPE CANAVERAL, Fla. — The U.S. Postal Service is going all out for this summer’s total solar eclipse, with a first-of-its kind stamp.
Just touch the stamp with your finger, and the heat transforms the image of the blacked-out sun into the moon. Remove your finger, and the eclipse reappears. The trick is using temperature-sensitive ink.
The ink is vulnerable to UV light; ironically, that means that the stamp should be kept out of direct sunlight to preserve the special effect, the U.