Cold, icy Pluto is so very far from the warmth and, more pertinently, the light of the sun. On our solar system's lonely dwarf planet, the sun appears roughly 150 times to 450 times brighter than the full moon from Earth, varying based on Pluto's distance from the sun due to its elliptical orbit.
To relate that to Earth terms, NASA calculated that the brightest time on Pluto in the middle of the day was equivalent a dim period at dawn and dusk on a clear day on Earth. It called this snapshot of time "Pluto Time", and launched a web tool that calculates Pluto Time in any given location and time of year around the world.
The social media campaign to photograph Pluto Time and send the photos to NASA launched in June. Since that time, over 7,000 photos of Pluto Time have been submitted from around the world.
You can, of course, view these photos via the Pluto Time web page, but NASA has been having some fun with them too. More specifically, the Solar System Exploration Public Engagement team at NASA's Jet Propulsion Laboratory in Pasadena, California, assembled thousands of the images into three photo mosaics: one of Pluto, one of Pluto's largest moon, Charon, and one of Pluto and Charon together.
Each mosaic contains between 1,500 and 2,100 photos, using software to select the right colours and shapes for Pluto's colours and shapes. And the resulting files are enormous: at full resolution, they would print out at 3.35 by 3.35 metres (11 by 11 feet).
The photos include landscapes, selfies, pets and famous landmarks, but there's also a secret homage. In the informally named Tombaugh Regio region of Pluto's now-famous "heart," the team included a photo of Clyde Tombaugh, who discovered Pluto in 1930, with his home-made nine-inch telescope.
"It's gratifying to see the global response to Pluto Time, which allowed us to imagine what it's like on Pluto, some three billion miles away," said NASA director of planetary science Jim Green. "This is a wonderful example of how space exploration and science unite us with a common bond."