Explained: Sunita Williams Experiences 16 Sunrises And Sunsets Every Day

For astronauts aboard the International Space Station (ISS), sunrise and sunset isn't a once-a-day occurrence. It happens as many as 16 times, and NASA astronaut Sunita Williams, currently on the ISS, is no stranger to this spectacular view. 

In 2013, when she was felicitated at the University of Gujarat in the presence of then Chief Minister Narendra Modi, Ms Williams reflected on this surreal experience. “Because I had wanted to go to space and worked hard for it, I was lucky to see 16 sunrises and 16 sunsets in a day in a fast-moving space shuttle,” the seasoned astronaut shared.

Her current journey to space was extended due to delays in the Boeing Starliner spacecraft's return schedule, keeping her in orbit until February 2025. Alongside fellow astronaut Butch Wilmore, Ms Williams is using this extra time to contribute to vital research and explore the unique experiences space offers, including the chance to see multiple sunrises and sunsets within 24 hours. But how does it happen?

The Science

Orbiting Earth at a speed of approximately 28,000 km per hour, the ISS completes a full orbit every 90 minutes. This rapid journey around the planet means astronauts witness a sunrise or sunset approximately every 45 minutes. For each orbit, they move from the dark side of Earth to the sunlit side and back again, experiencing what most people only see twice a day.

Day-Night Cycle In Space

Unlike life on Earth, where a day consists of about 12 hours of light and 12 hours of darkness, astronauts experience 45 minutes of daylight followed by 45 minutes of darkness repeatedly throughout their day. This rapid cycle creates a continuous rhythm of day and night, occurring 16 times within a single Earth day.

How Astronauts Mark Time In Space

For astronauts on the International Space Station (ISS), traditional day and night rhythms don't apply when they circle the planet every 90 minutes. In the absence of natural daylight patterns, astronauts rely on Coordinated Universal Time (UTC) to structure their schedules. Daily routines on the ISS are highly regimented, with work, meals, and rest scheduled in five-minute intervals. This rigorous routine is critical to maintaining both physical and mental health in a setting so far removed from Earth's natural cycles.

To stay synchronised with their teams on Earth, astronauts use atomic clocks, which provide extreme precision and are essential for navigation, particularly in missions beyond Earth's orbit.