NASA's Sunita Williams witnesses 16 sunrises, sunsets daily in space, here’s how

NASA astronaut Sunita Williams has had the rare privilege of experiencing an extraordinary view aboard the International Space Station (ISS): 16 sunrises and sunsets each day. This phenomenon is due to the ISS’s rapid orbit around Earth. Williams, reflecting on her time in space in 2013, mentioned that after her hard work to reach space, she was "lucky to see 16 sunrises and 16 sunsets daily aboard a fast-moving space shuttle." This experience continues as she remains stationed on the ISS.

How multiple sunrises and sunsets occur

The ISS orbits Earth at an impressive speed of around 28,000 kilometers per hour, completing a full orbit in about 90 minutes. This means that astronauts on board witness a sunrise or sunset every 45 minutes. Over a 24-hour period, this results in 16 complete day-night cycles, a stark contrast to Earth’s typical 12-hour rhythm of day and night. In each 90-minute orbit, the ISS transitions between sunlight and darkness as it travels over different parts of Earth. This unique cycle repeats throughout the day, providing astronauts with a fast-paced sequence of light and dark.

Maintaining routine in space

The rapid sequence of sunrises and sunsets makes it impossible for astronauts to rely on natural cues for sleep. On Earth, we typically use the Sun’s rise and set as signals for waking and sleeping, but in space, a different approach is required. Astronauts aboard the ISS follow a tightly regulated schedule based on Coordinated Universal Time (UTC), which keeps them synchronized with operations back on Earth. The schedule is split into segments of roughly 5 minutes for work, exercise, meals, and rest to maintain both physical and mental well-being. Without regular day-night cycles, this strict schedule is essential to prevent disorientation and fatigue, especially during the long-duration missions common on the ISS.

Additionally, the astronauts depend on precise atomic clocks to coordinate with Earth’s mission control and, in future deep-space missions, these clocks will become even more critical for navigation and communication.

Sunita Williams’ ongoing mission

Sunita Williams has been on the ISS since June 2023, although her return to Earth has faced delays due to technical issues with Boeing’s Starliner capsule. She is now scheduled to return aboard SpaceX’s Crew Dragon in February 2025. This extension in her mission not only adds to her time in space but also gives her additional opportunities to witness the awe-inspiring cycle of 16 sunrises and sunsets each day. Her continued stay highlights the resilience of astronauts and the complex logistics involved in space travel and re-entry, ensuring they stay connected with Earth while adapting to the unique demands of life in space.

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