The International Space Station (ISS) orbits Earth at a height of approximately 400 kilometres. It takes 90 minutes for the ISS to make one complete turn around the Earth. Day and night on board the ISS are different from day and night on Earth...
Let’s try to understand why!
When is it day on Earth? When is it night? The following diagram represents the ISS turning around the Earth (on the right), and the Sun (on the left).
When the ISS is in position A, does it see the light from the Sun? Is it daytime or night-time on board?
- When the ISS is behind the Earth (position B), does it see the light from the Sun? Is it daytime or night-time on board?
Activity: Divide the class into groups of three: one child is the Earth, one child is the Sun and the third one is the ISS.
The Sun is standing facing the Earth at 3 metres distance. It does not move at all during the activity. It counts how many times the ISS passes between the Earth and itself.
The Earth is standing still; it stays at the same place but rotates on its own axis. It counts out loud and very slowly from 1 to 16. As it counts, it rotates slowly so that it faces the corresponding number (see drawing, for example: as it says “4” the Earth should be facing into direction 4, etc…) To make it easier you can write the numbers down on different pieces of paper and tape them to the walls of the classroom
- The ISS is walking around the Earth at one metre distance. It should complete one turn every time the Earth counts, and should exactly face the Earth as it pronounces the number.
Ask the Suns how many times the ISS passed between the Earth and itself during one complete rotation of the Earth.
The ISS orbits the Earth in 90 minutes. The Earth rotates on itself in 24 hours (24 hours = 16 times 90 minutes). Can you compare these movements with the activity we have just realised?
Do you think an astronaut can use the day/night-time on board the ISS to know when he should be awake or sleeping? What time is it on board the ISS?
- 4. How many sunsets can an astronaut see from the window of the International Space Station during one Earth day?