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© Copyright 1997, Jim Loy
I've heard several people say that the Great Wall of China is the only man-made structure that can be seen from outer space. Once, I even read that the Great Barrier Reef, off the coast of Australia, is the only structure on earth, made by a form of life, that can be seen from outer space. The Great Barrier Reef is huge, dwarfing anything that humans have made, and it was built by corals, which are small sea animals. But, it turns out, all sorts of human creations can be seen from space, at least from Earth orbit.
I once saw a photo, from a Gemini mission, which startled me. It was a photo of the border between Alberta and Montana, part of the Canada/USA border. This photo showed a very distinct line, running East and West. How could something like that show up? That border is marked on globes, but on the Earth itself? It turns out that that part of Montana is largely wheat fields, while that part of Alberta is largely range land for cattle. Similar change in farm or ranch land can be seen all over the world. Circular plots of land, irrigated by pivot sprinkler systems, are especially easy to spot, because of large clusters of these green circles, often in deserts.
Cities can be seen from space, especially at night. Harbors can be seen.
Factories can be seen, by their smoke and sometimes by the water pollution that spews into rivers and harbors. Forest fires can be seen from space, and many are human-made.
Individual buildings, like the Astrodome and the Pentagon can be seen from space. But, smaller buildings have been photographed, including individual houses. Ships can be seen, usually because of their distinctive wakes.
Supposedly, spy satellites can spot individual people. Maybe they can't read Sadaam Husein's lips, yet.
Incidentally, when I was young I wanted to be an astronaut. You see, my teachers claimed that I was just taking up space.
Addendum: Astronauts say that it is very difficult to see the Great Wall of China from space.