On Monday, August 21st, the continental US will experience its first total solar eclipse since 1979. And to get the country prepared, the Postal Service is releasing a heat-reactive commemorative stamp. The stamp is printed using thermochromic ink, and when rubbed using fingers or thumbs it will react to body heat, changing from an image of a total solar eclipse to a picture of the Moon. And, if you’re someone who loves to get your astronomical news from stamps, the back of the will also show a map of where to best view the eclipse.

If you’ve forgotten your high school science lessons, a total solar eclipse happens when the Moon moves between the Sun and the Earth, blocking out the former’s light. The Moon casts a shadow that moves across the surface of the Earth in what’s called a “path of totality.” On August 21st, this 67-mile-wide path will travel west to east across mainland America, crossing 14 states as it moves from Oregon to South Carolina. In any given point on the path, the total solar eclipse will be viewable for approximately two minutes.

”Tens of millions of people in the United States hope to view this rare event, which has not been seen on the U.S. mainland since 1979," said the Postal Service in a statement. And if you miss it, you can always buy the stamp.