How Do Astronauts Aboard The ISS Know When It s Day Or Night

Days and nights are essential phenomena caused by the Earth's rotation, affecting not only our daily activities, but also our biological systems. For astronauts stationed on the International Space Station, however, this regular cycle is profoundly different. On Earth, the rotation of our planet gives us approximately 24-hour days, with around 12 hours of light and 12 hours of darkness. The ISS, however, orbits the Earth every 90 minutes, which means it experiences about 45 minutes of sunlight and 45 minutes of darkness during each revolution. Within 24 hours, the ISS experiences 16 sunrises and 16 sunsets, heavily disrupting the human body's circadian rhythm, which naturally operate on a 24-hour basis. To avoid confusion and maintain some semblance of normalcy, the ISS operates on Universal Coordinated Time, or UTC. This not only regularizes the sleep and work cycles of the astronauts, but also facilitates effective collaboration between the multinational agencies involved in the project. Even so, this doesn't completely solve the sleep problems experienced by the astronauts due to rapidly changing light conditions. To address this issue, scientists altered the lighting system on the space station. Initially, the ISS used general luminaire assemblies with fluorescent lamps for lighting. In 2016, these were swapped for solid-state LED modules that emit different wavelengths at varying intensities to simulate a day-night environment. The lights are set to a high brightness in the morning, a bluer wavelength for challenging tasks, and warmer tones towards the end of the day to promote rest. Activities on the ISS commence at 6 a.m. UTC and end at 9.30 p.m. UTC. After 9.30 p.m., the lights are dimmed to emulate nighttime, ensuring that crew members can comfortably rest, thus improving their efficiency. These modifications in the lighting have not only benefited inhabitants of the ISS, but were also instrumental in the wider commercialization of LED products, such as mood lights. Though strict schedules are adhered to aboard the ISS, astronauts have the rare opportunity to enjoy a full day in just 90 minutes by looking out the cupola of the ISS, offering an incredible view of the Earth's sunrises and sunsets, along with the endless cosmos beyond. If you enjoyed this video, we'd love to hear from you in the comments section. Your feedback not only supports us, but also helps our channel reach more viewers and continue to grow.