Move over, flags, flowers, and birds. A new postage stamp is coming to town—just in time for a huge solar eclipse.

On August 21, the Earth, Moon, and Sun will line up. The Moon will act like the middle person in a game of monkey-in-the-middle. It will block sunlight and cast a huge shadow on Earth. Day will turn to night in the United States—but only in the eclipse’s “path of totality.” That’s a 70-mile-wide strip. It will touch 14 U.S. states along its path. People in Oregon will see the eclipse first. People in South Carolina will see it last.

For sky watchers, the eclipse is a big deal. A solar eclipse has not crossed the United States from coast to coast for almost 100 years! But it’s also a big deal to philatelists. (Fuh-LAT-uh-lists is a big word for “stamp collectors.”) In honor of the eclipse, the U.S. Postal Service will release a one-of-a-kind stamp on June 20. The stamp doesn’t just use an image to show an eclipse. It acts out an eclipse. At first, the image on the stamp shows a total eclipse. (In a total eclipse, you can’t see the Sun. But you can see its corona—the bright atmosphere just outside it.) When you touch the stamp, the ink will react to the warmth of your finger. A new image will appear. Instead of the eclipse, you will see the full Moon. Totally cool!

The Postal Service will also sell protective envelopes to help keep the thermochromic (heat-sensitive) ink from wearing out. Even without fancy envelopes, the stamps will last much longer than the eclipse does. In most places, the eclipse will be over in just two-and-a-half minutes!