Astronauts on the International Space Station see sunrise far more often than people on Earth. Instead of one sunrise each day, they see about sixteen because the station races around Earth in about 90 minutes. Each orbit carries the ISS from the dark side of Earth into sunlight, creating a new orbital sunrise.
This makes orbital sunrise a clear example of how motion, light, and shadows work in space.
The Sun is always shining on one side of Earth, while the other side lies in Earth’s shadow. As the ISS follows its curved path around Earth, it repeatedly enters the shadow and then exits back into sunlight. The moment it leaves the shadow, astronauts see the Sun rise over Earth’s edge, called the limb.
Since a full day has 1440 minutes, a 90 minute orbit gives about 1440 ÷ 90 = 16 sunrises per day.
Key Facts
- The ISS completes one orbit around Earth in about 90 minutes.
- Number of ISS orbits per day = 1440 minutes ÷ 90 minutes = 16 orbits.
- Astronauts see about 16 sunrises and 16 sunsets each Earth day.
- Orbital sunrise happens when the ISS moves from Earth’s shadow into sunlight.
- The ISS travels about 28,000 km/h, fast enough to circle Earth many times per day.
- Earth’s shadow is caused when Earth blocks sunlight from reaching part of the ISS orbit.
Vocabulary
- Orbit
- An orbit is the curved path an object follows around a planet, moon, star, or other body in space.
- International Space Station
- The International Space Station, or ISS, is a large spacecraft where astronauts live and work while orbiting Earth.
- Orbital Sunrise
- An orbital sunrise is the moment a spacecraft moves out of Earth’s shadow and back into sunlight.
- Earth’s Shadow
- Earth’s shadow is the dark region behind Earth where sunlight is blocked by the planet.
- Limb
- The limb is the visible curved edge of a planet or moon seen against space.
Common Mistakes to Avoid
- Thinking the Sun rises because it moves around the ISS. This is wrong because the ISS is moving rapidly around Earth while the Sun stays in nearly the same direction during one orbit.
- Counting only one sunrise per day in space. This is wrong because a sunrise happens every time the ISS exits Earth’s shadow, which occurs about once per 90 minute orbit.
- Assuming Earth’s shadow means the Sun turns off. This is wrong because the Sun keeps shining, but Earth blocks the sunlight from reaching the ISS for part of its orbit.
- Using 24 instead of 1440 when dividing by 90 minutes. This is wrong because 24 is in hours, and the orbit time is given in minutes, so the units must match.
Practice Questions
- 1 The ISS completes one orbit in 90 minutes. How many orbits does it complete in 24 hours? Use 24 hours = 1440 minutes.
- 2 If astronauts see one sunrise each orbit, how many sunrises would they see during a 6 hour period? Use 1 orbit = 90 minutes.
- 3 Explain why astronauts on the ISS can see many sunrises in one day even though people on Earth usually see only one.