People living in the space station have to get used to all kinds of changes from life on Earth. It takes them only 90 minutes to orbit (go around) the earth, so the sun looks as if it is rising and setting 16 times a day. This can be confusing, especially when one is trying to decide when they should go to bed. The astronauts try to keep a 24-hour-schedule anyway. At bedtime, they have to sleep in sleeping bags that are stuck to the wall. They have to strap themselves inside so they will not float away while sleeping.