On Monday, August 21, a total solar eclipse will make its way across the US, a rare event that was last seen in 1979.
In honor of this awesome moment, the US Postal Service is going to release some neat stamps that change when you rub your finger on them. Come on, that’s kind of cool right?
The stamp will use thermochromic ink to change the image when heat is applied, such as rubbing it with your finger. The initial image will show a picture of the eclipse taken by astrophysicist Fred Espenak from Libya in 2006. Rubbing it will reveal an underlying image of the Full Moon, also taken by Espenak.
The stamps, designed by Antonio Alcalá of Alexandria, Virginia, will be available nationwide and in post offices on June 20, a spokesperson for the USPS told IFLScience. They can also be pre-ordered from usps.com/shop.
“Thermochromic inks are vulnerable to UV light and should be kept out of direct sunlight as much as possible to preserve this special effect,” the USPS noted, adding it was the first time thermochromic ink had been used in US stamps.
On the back is a map showing the path of the eclipse. © 2017 USPS
A total eclipse is caused by the mathematical oddity in which the Sun’s disk is 400 times greater than the Moon’s, but the Moon is 400 times closer to Earth. With the Moon in orbit around Earth, there are times when it passes directly in front of the Sun from our point of view and blocks its light, sometimes entirely (a total eclipse) and sometimes just a bit (known as an annular or partial eclipse).
There are actually two total solar eclipses around the world every three years on average, and many more partial eclipses (when the Moon covers only part of the Sun’s surface). But the shadow caused by totality is relatively small, so seeing it from a particular location is rare.
For this upcoming eclipse, it will be the first time since 1918 that the Moon’s shadow (about 110 kilometers or 70 miles wide) will cross from the Pacific west coast of the US to the Atlantic east coast. It will pass through 14 states during the course of August 21, including Oregon, Kansas, Illinois, and North Carolina.
It will take the Moon more than three hours to cross the Sun, but the actual period of totality is much smaller – about two minutes, depending on where you are. The best viewing locations are likely to be in the western US, which is less prone to afternoon summer thundershowers than the southeast.
The next total solar eclipse that will be visible in the US will be in 2024, and after that it’s 2045. But at least you can have a commemorative stamp to remember this one, right?