Photo: National Aeronautics and Space Administration · Public domain
16
Astronauts on the space station see about 16 sunrises every day.
5 min readLast updated
The short answer
Yes. The International Space Station orbits Earth about every 90 minutes at roughly 28,000 kilometers per hour, so its crew passes from night into day around 16 times every 24 hours.
Why it's true
The station flies about 400 kilometers above Earth. To stay in orbit at that height, it must travel at about 28,000 kilometers per hour, or roughly eight kilometers every second. At that speed, one full lap of the planet takes around 90 minutes, and the station completes about 15 to 16 orbits a day.
On each orbit it crosses from Earth's sunlit side to its dark side and back. That means a sunset roughly every 90 minutes, followed about 45 minutes later by a sunrise. Seen from the station, each sunrise is a fast, vivid band of colour sweeping along the curved horizon, lasting only seconds.
Astronauts often describe these orbital sunrises as one of the most beautiful sights of their missions.
By the numbers
~400 km
Typical altitude
~28,000 km/h
Orbital speed
~90 min
Time for one orbit
2000
Continuously crewed since
The backstory
The first long term crew, Expedition 1, arrived at the station on 2 November 2000, and people have lived aboard continuously ever since. The station was assembled piece by piece in orbit by several space agencies, including NASA, Roscosmos, the European Space Agency, Japan's JAXA and the Canadian Space Agency. End to end it is about 109 meters long, close to the length of an American football field.
With the Sun rising and setting so often, the crew cannot live by what they see outside. They follow a schedule based on Coordinated Universal Time, with planned work, exercise and sleep periods. Window shades, sleep masks and carefully timed lighting help their bodies keep a normal daily rhythm despite the constant swings between day and night.
Why 90 minutes matters for science
Frequent day night cycles expose experiments to dramatic temperature swings. Outside the station, surfaces can move from well over 100 degrees Celsius in sunlight to far below freezing in shadow.
Engineers design the station's radiators, insulation and equipment to cope with these swings, which repeat thousands of times a year.
Worth remembering
- The ISS orbits Earth about every 90 minutes.
- Its crew experiences around 16 sunrises and sunsets a day.
- Astronauts keep a normal schedule using Coordinated Universal Time.
In context
Orbiting is really falling. The station is pulled toward Earth by gravity, but it moves sideways so fast that the ground curves away beneath it as quickly as it falls. That balance is what keeps it circling, and it is why speed and altitude are so tightly linked for anything in orbit.
Lower orbits are faster and higher ones slower. The Moon, about 384,000 kilometers away, takes about 27 days to go around once, while satellites near the station's height zip around in an hour and a half.
A closer look
What a sunrise looks like from orbit
Because the station moves so quickly, the Sun seems to leap above the horizon. Light passes through thin layers of atmosphere along the edge of the planet, creating bands of red, orange and blue.
Astronauts have photographed these bands many times. They show how thin Earth's atmosphere looks from above, like a narrow glowing line.
Keeping the station up
At 400 kilometers there is still a trace of atmosphere. It creates a tiny drag that slowly lowers the station's orbit.
Engines on the station or on visiting spacecraft fire from time to time in reboosts, lifting it back to the right altitude.
Body clocks in space
Human circadian rhythms rely heavily on light. Rapid day night cycles can disrupt sleep, so the station has adjustable lighting that shifts colour and brightness through the day.
Research aboard the station on sleep and lighting has helped design better lighting for people on Earth who work night shifts.
Related facts
The station's height has other surprising effects astronauts are often the nearest people to Point Nemo.
For more about the light those sunrises bring sunlight is about 8 minutes old.
Compare with a telescope much farther away Webb does not orbit Earth at all.
Fast moving satellites face strange physics GPS needs Einstein's relativity.
Key terms
- Orbit
- The curved path an object follows as it falls around a planet or star.
- Low Earth orbit
- Orbits up to about 2,000 kilometers above Earth, where the station flies.
- Circadian rhythm
- The body's roughly 24 hour internal clock that controls sleep and alertness.
Myth vs reality
Myth
Astronauts float because there is no gravity in orbit.
Reality
Gravity at the station's height is about 90 percent of the surface value. Crews float because they are constantly falling around Earth.
People also ask
How fast does the International Space Station travel?
About 28,000 kilometers per hour, or roughly 17,500 miles per hour. That speed keeps it in orbit about 400 kilometers above Earth.
How many times does the ISS orbit Earth each day?
Around 15 to 16 times. Each orbit takes about 90 minutes, which is why crews see so many sunrises and sunsets.
What time zone do astronauts use?
The station runs on Coordinated Universal Time, essentially Greenwich Mean Time. It is a neutral choice that works for the international partners.
How do astronauts sleep with so many sunrises?
They follow a fixed schedule, sleep in small crew quarters, and use window covers, eye masks and lighting designed to support a normal body clock.
Can you see the space station from the ground?
Yes. It often appears as a bright, steady moving light shortly after sunset or before sunrise. NASA's Spot the Station service lists sighting times.
