NASA astronaut Sunita Williams has the rare experience of witnessing 16 sunrises and sunsets each day while aboard the International Space Station (ISS). Reflecting in 2013, Williams said, “After working hard to get to space, I was fortunate to see 16 sunrises and 16 sunsets daily aboard a fast-moving space shuttle.”
The ISS orbits Earth every 90 minutes at around 28,000 km/h, meaning astronauts observe a sunrise or sunset every 45 minutes. Consequently, those aboard experience 16 day-night cycles in a single Earth day, which is far more rapid than the typical 12-hour cycle of day and night on Earth. This creates a unique pattern of transitioning between light and darkness every 45 minutes, repeating 16 times a day.
Due to the lack of natural day-night cycles in space, astronauts adhere to Coordinated Universal Time (UTC) for their schedules. Their day is meticulously divided into brief intervals for tasks such as work, exercise, meals, and rest, which helps them sustain mental and physical well-being in space.
On Earth, people’s sleep-wake cycles are guided by the natural rise and setting of the Sun, a routine unavailable to astronauts in orbit, where the Sun doesn’t rise and set in a conventional way. The ISS’s rapid orbiting necessitates a fixed schedule, and astronauts rely on UTC to maintain balance amid their demanding tasks.
Sunita Williams, currently stationed on the ISS since June 2023, faced delays in her return due to Boeing’s Starliner issues. She is now expected to return to Earth in February 2025 aboard SpaceX’s Crew Dragon.
The extended stay has given Williams even more time to adapt to the fast-paced environment aboard the ISS and to carry out critical experiments and maintenance work. This delay highlights the challenges and unpredictability of space missions, where factors like technical issues and evolving timelines often demand resilience and flexibility from astronauts.
During her mission, Williams has engaged in a wide range of scientific research aimed at better understanding how the human body copes in microgravity over extended periods. Experiments have included studies on muscle atrophy, bone density loss, and sleep patterns—all key aspects of preparing for future long-term space exploration. These studies provide valuable insights that could help support the feasibility of future missions to Mars or beyond, where astronauts will face even greater challenges.
Beyond research, Sunita Williams has also played a crucial role in maintaining the ISS’s operational systems, conducting spacewalks to install new equipment, and troubleshooting any unexpected issues that arise. Spacewalks, often lasting several hours, require immense physical and mental preparation, further underlining the rigorous schedule and the demanding conditions astronauts endure in orbit.
Living on the ISS also involves building strong connections with Earth-based mission control and other space agencies, as collaboration and constant communication are essential for mission success. For Williams, coordinating with teams from NASA, SpaceX, and international partners has been pivotal, especially with the recent shift to SpaceX’s Crew Dragon for her return.
Despite the challenges of life in space, Williams has often spoken about the awe of viewing Earth from above and the profound impact it has on her perspective. The opportunity to see our planet as a single, interconnected entity reinforces her commitment to advancing space exploration for the benefit of all humankind. Her journey back to Earth in 2025 will mark the end of yet another remarkable chapter in her distinguished career, adding to her legacy as a pioneering astronaut who has broken barriers and expanded the boundaries of human exploration.
