There’s an extension of the XKCD site that poses the question “What if” on various scenarios. Like:
If you could teleport to a random place of the surface of the Earth, what are the odds that you’ll see signs of intelligent life?
Of course, the first answer is you’ll probably land in water.
But the most interesting answer is this:
Wait for nightfall.
At any given time, there are hundreds of satellites in the sky. Most of them are too faint to see, but if you’re in an area without much light pollution, and you look carefully enough, there’s virtually always a satellite visible. Their rapid motion across the sky and various highly inclined orbits make them unlikely to be anything but artificial.
It’s often said that the Great Wall of China is the only human artifact that can be seen from space. This is wrong.
But in my opinion, the real problem with this factoid isn’t that it’s wrong—it’s that it overlooks a much cooler point. The Great Wall of China may not be the only artifact on Earth that you can see from a satellite … but our satellites are the only human artifacts that you can see from everywhere on Earth.
Want to see signs of intelligent life? Just look up.
When I lived in England, I used to go out at night and watch the satellites in the sky. Since I was living in the countryside, there was no light pollution, and the sky was always loaded with more stars than I had ever seen in my life. And amid all those stars, you could see shiny objects move across the sky, very small, but always there. If you live in the city, you’ll never see that.