Some of you reading this are young enough to get a realistic chance to travel into space sometime in the future. When you look down on Earth, what do you expect to see? Yes, there will be oceans and continents, and even large lakes, but will there be any signs of human handiwork?

This question is addressed in “What Human-made Structures can be Seen From Space?” by Joe Phelan on the LiveScience website (https://www.livescience.com/human-made-structures-seen-from-space?).

First, the article defines where space begins. The most widely accepted definition is the Kármán line, named after physicist Theodore von Kármán. It’s usually defined as 100 kilometers (62 miles) above Earth’s surface. So assuming we’re just above that line, what should we look for?

Many people automatically think one observable structure would be the Great Wall of China. Nope, at least not with the naked eye. It’s really long, but just too narrow. The most visible man-made structure to date is actually the Bingham Canyon Mine, about 20 miles (32 km) southeast of Salt Lake City. As the largest human-made excavation in history and also the deepest “open-pit” mine in the world, it has been seen from the Space Shuttle, which orbited at an altitude of between 190 and 330 miles.

According to NASA, China’s Three Gorges Dam across the Yangtze River is also visible from space. At 607 feet (185 m) tall and more than 1.2 miles (2 km) long, it’s easily the largest power-producing facility in the world.

How about Egypt’s Pyramids of Giza? Here there is some disagreement. Leroy Chiao, a former NASA astronaut and ISS commander, insists he spotted the pyramids while in orbit, although others are skeptical. Cities can also be seen, although they look like grey blobs. For more examples, please check the article.

In my lifetime, I’ve seen the introduction of jet aircraft and the beginning of space travel. If you see the same advances in your lifetimes, I expect you’ll be able to test your eyesight from the Kármán line yourselves.