Since its first launch in 1998, up 9 astronauts permanently occupy the International Space Station. Confined in their solitude, away from sunlight, astronauts paradoxically see the immense space that surrounds the Earth, while they themselves are kept in a small space considerably. They glide at the speed of 7.7 km / s in low Earth orbit and eyes traverse the vast land areas scrolling "under" the station. They attend every day about 16 sunrises and sunsets. But it is "downward" in the night they see their only horizon, the Earth.
The spectacle of the night offers them red and green lights, as well as lights of big terrestrial cities with in the background, multicolored stars. The atmosphere of the Earth reflects sunlight..
nota: Weightlessness or zero gravity?
The term zero gravity that is used in everyday language, but today it is preferred that weightlessness. Weightlessness is a theoretical state because it does not exist in the universe, there is always in the cosmos a residual gravity. On board a spacecraft, speaking generally microgravity. Microgravity has a value of one millionth of the Earth's gravity.
Image: The first free flight of an astronaut in space, dates from 1984. Astronaut Bruce McCandless became the first man to move freely with an MMU (Manned Maneuvering Unit), it is propelled by jets nitrogen. One can easily imagine the anxiety can feel a man flying at 27 700 km / h in this state of weightlessness, with as horizon our planet.
Image: The International Space Station is a 400-ton structure, stuffed with technology. With its 110 meters wide, 74 meters long and 30 meters high, the station orbit at 340 km altitude. Here, the NASA astronaut Reid Wiseman when preparing the launch of May 19, 2014 in Kazakhstan. Its only horizon is his cabin.