International Space Station

The station orbits about four hundred kilometres up, less than the distance from London to Edinburgh. At that height it has to move at roughly 7.7 kilometres a second to stay up, so it goes around the planet in a little over an hour and a half. The people aboard see the sun rise and set about sixteen times in a day and keep to Greenwich time, a compromise between the clocks in Houston and Moscow.

No rocket carried it up whole. It was assembled in orbit, one piece at a time. The first piece went up in 1998, the first long-stay crew arrived in late 2000, and the last large module arrived in 2021, twenty-three years after the first. The finished structure is about a hundred and ten metres from one end of its solar wings to the other and weighs around four hundred and twenty tonnes. Five space agencies run it together, and it has hosted people from more than twenty countries.

The thin air at that altitude is still air. It drags on the station a little every day, and left alone the orbit would decay within a few years, so visiting spacecraft periodically push it back up. That is also how it will end. The plan is to lower it deliberately into the Pacific around 2030, and to have commercial stations flying by then to take its place.

It can be seen without any equipment. It appears for a few minutes around dusk or dawn, when the ground is dark but the station is still in sunlight, as a steady white point moving faster than any aircraft and never blinking. Space agencies publish the pass times for any town.