The images are available to the public through The Gateway to Astronaut Photography of Earth, the most complete online collection of images of Earth taken by astronauts. This database contains photographs beginning with those taken during Mercury missions in the early 1960s up to recent images from the station, with more added daily. As of August 2014, the collection included a total of nearly 1.8 million images, more than 1.3 million of them from the space station. Approximately 30 percent of those were taken at night.

via Space Station Sharper Images of Earth at Night Crowdsourced For Science | NASA.

Lost at Night requires the most skill, seeking to identify cities in images encompassing a circle 310 miles around. “We don’t know which direction the astronaut pointed the camera, only where the station was at the time the image was taken,” explains Sanchez. “Some images are bright cities but others are small towns. It is like a puzzle with 300,000 pieces.”