On the ISS, astronauts see 16 sunrises every day as the station circles Earth, but their bodies refuse to follow the 90-minute cycle, forcing crews to stick to a familiar 24-hour routine despite living through multiple days and nights

If you watched Earth from the International Space Station, sunrise would quickly lose its usual meaning. The ISS circles Earth roughly once every 90 minutes, so astronauts can see about 16 sunrises and 16 sunsets during a 24-hour period, as per a report.

But they do not start a new day every time the Sun appears. Instead, astronauts follow a carefully managed 24-hour schedule while the station repeatedly moves between darkness and daylight outside the windows. Their bodies can experience changes in sleep and circadian timing in space, but the station's 90-minute orbit does not become their biological day.