M: Glaciers in the Tian Shan mountains in Kyrgyzstan.

It took Adam P. Voiland three years and the help of readers and colleagues to “find an alphabet in the sky.” In August 2015, he clinched it.

With the addition of “M” – captured in an image of glaciers in the mountains of Kyrgyzstan – the NASA science writer and social media manager completed the collection of all 26 letters of the alphabet depicted in gorgeous natural wonders photographed by NASA satellites and astronauts.

The “Reading the ABCs from Space” project started in 2012, when Voiland spied a giant letter “V” in a satellite shot of smoke drifting over mountains in northern Canada. “It made me wonder how many other letters have satellites captured momentarily gracing Earth’s atmosphere and oceans,” he wrote in the NASA Earth Observatory blog.

Voiland, who works at the NASA Earth Observatory at Goddard Space Flight Center in Greenbelt, Maryland, invited others to join in the hunt, searching imagery at several NASA sites for letters hidden in “the ceaseless mixing and swirling of clouds, smoke, dust, ice and even phytoplankton that constantly occurs across our planet.” He documented each letter shape as it was identified, noting where the image was taken, the date and time.

Some letters – “O” and “C” – were easy to find, he wrote. Others, including “A,” “B” and “R” were tough.

See the remarkable series, released in December, starting with a lowercase cursive “A”: