NASA astronaut Sunita Williams has the unique opportunity to witness 16 sunrises and sunsets every day aboard the International Space Station (ISS). In 2013, Williams said: “After working hard to get to space, I was lucky enough to see 16 sunrises and 16 sunsets a day aboard a fast space shuttle. »

How do multiple sunrises and sunsets occur?

Every 90 minutes, the ISS completes a full orbit around Earth at a speed of about 28,000 km/h, meaning astronauts see a sunrise or sunset every 45 minutes. The astronauts aboard the SSI experience 16 day-night cycles in a single earth day. The ISS moves at a much faster pace than life on Earth, where day and night typically last about 12 hours. Astronauts experience a transition between light and dark every 45 minutes, creating a unique cycle that repeats 16 times per day.

How do astronauts know when to sleep?

Astronauts follow a schedule based on Coordinated Universal Time (UTC) because there are no regular day-night cycles in space. Their days are divided into periods of approximately 5 minutes for work, exercise, food and rest, a schedule they strictly adhere to in order to maintain their mental and physical health in space.

On Earth, humans use sunrise and sunset as indicators of sleep and wake cycles. However, in space, astronauts do not have these natural cues because the Sun does not rise or set in the same way. As a result, the constant movement of the ISS creates the need for a fixed schedule, and astronauts follow UTC to maintain a balanced lifestyle alongside their demanding work schedules.

Astronauts also rely on precise atomic clocks to stay in sync with Earth-based teams, which is especially crucial for navigation on deep space missions.

Sunita Williamsa NASA astronaut stationed on the International Space Station since June 2023, faced delays in his return to Earth due to problems with Boeing’s Starliner. She is now expected to return to Earth in February 2025 aboard SpaceX’s Crew Dragon.