Citizen science projects, which have gained a great deal of popularity in recent years, invite citizens from around the world to participate in scientific data gathering and analysis. Such projects enable scientists to explore research questions on a large scale thanks to the contributions of citizen scientists. We've featured a number of unique citizen science projects this past year, but one of our favorites is Cities at Night. What makes this project stand out is the fascinating material at the center of the project: photographs from the International Space Station that depict cities all around the globe. Through these photographs, Cities at Night provides important insight into the growing problem of light pollution. Astronauts on board the International Space Station (ISS) take hundreds of night-time pictures each year of cities around the globe. Cities at Night is a "citizen science project that aims to create a map, similar to Google maps, of the Earth at night using night-time color photographs taken by astronauts onboard the ISS." As the project team explains, human expertise is more effective at classifying and geo-referencing these photos than an algorithm. In the Maps section of this website, visitors can help the project team with these processes via a series of links (dark skies, lost at night, and night cities). In addition, this section contains photographs that have already been classified and geo-referenced by previous users, which are organized via a series of maps. The Cities at Night project is intended to collect information about light pollution: an issue that visitors may learn more about via the light pollution and research tabs, respectively.