It started with a plume of smoke in the shape of a ‘V’ on an image of Earth taken by one of NASA’s satellites. Soon it grew into an addictive hunt for more letters, made out of glaciers, storms, lakes and craters.
For years, NASA science writer Adam Voiland has been on the lookout for letter-shaped natural phenomena, combing through thousands of satellite images slowly collecting the entire alphabet and chronicling it in an online gallery. It was a hit, and soon Voiland was back for a second round, collecting another entire alphabet, this one all capitals, for a new children’s book, ABCs from Space.
Finding Earth’s alphabet involved a lot of scrolling through NASA’s Worldview or Google Maps in satellite mode, late into the night. Along the way, Voiland learned where some letters are more likely to hide. For instance, fjords, glaciers, and sea ice are good places to look for characters with lots of straight lines, like A, X, E and W.
The hardest letter to find? “R, for sure,” Voiland says. “Turns out that nature doesn't like to put curved, straight, and diagonal lines right next to each other.”
Though it could get tedious, the hunt was also rewarding, especially when a satellite just happened to catch the clouds as they formed a perfect shape. “For the H, there is something about the way the wind has dispersed those ship track clouds a little and given them just the right amount of texture that is absolutely stunning,” he says (see below).
Some of the letters are more exotic, like the ‘O’ formed by Africa’s Richat Structure (see NAT GEO image at the top of the post). This mysterious circular feature in Mauritania, also known as the Eye of the Sahara, has confounded geologists. Some thought such a perfect circle had to be an impact crater, formed when an asteroid crashed into Earth. Others argued that it was the remnant of an extinct volcano. The favored theory today is that it is an eroded geologic dome.
The 'G' in “NAT GEO” is tropical storm Douglas captured on July 4, 2014 by NASA’s Terra satellite. Many of the letters, including this one, are “false-color” images that are produced by wavelengths of light that humans can’t see with the naked eye. Scientists use these wavelengths to study things like changes in vegetation, which shows up as bright red when viewed with near-infrared light.
Shortwave infrared light can help distinguish between snow (which shows up as orange), ice (red), and clouds (peach). In true-color satellite images, all three are white and can be hard to tell apart. In the image of Douglas, the shortwave infrared light causes clouds with ice crystals in them to show up in orange while clouds made entirely of liquid water are white. The false color has the added benefit of creating some very beautiful and otherworldly images.
If readers want to know more about what’s in the images, notes in the back of the book explain all the various natural features that make up the letters. There’s also a map of where on Earth all the letters were found. Voiland hopes the ABCs from space will fuel kids’ curiosity about the Earth. “I think it would be really cool if people got inspired to do their own satellite ABC hunt with their kids,” he says.
Though he’s tracked down the entire alphabet more than once, Voiland is always ready for more. In fact, he sleuthed out a brand new ‘A’ and ‘T’ for the “NAT GEO” image in this post. And he says there are still a few natural features on his wish list: “How cool would a letter spelled in hot, flowing lava be, for instance?”