These are only going to be available for a limited time. If you are a stamp collector you should pick up a set.

There will be a solar eclipse that cuts right across the USA on Aug 21, 2017. It's a rare event and particularly rare in how it crosses the country.

The USPS has issued a unique stamp to commemorate the event.

The total eclipse stamps are thermochromic in that if you press your finger on one of the stamps the moon is revealed underneath. Fun and unique little stamp. You can buy them at the post office for face value. You can also buy them on Amazon for a bit of a mark up.

Total Eclipse of the Sun - USPS Forever Stamps Sheet of 16 - New 2017 Release

Here is a sheet of the stamps.

You press a finger on a stamp...

And the moon appears.

Here is the NASA map that shows the path of the eclipse. You can download the official NASA map pdf here.