What makes the Great Wall of China the only man-made object visible from space?

Category: Space
Published: December 11, 2012

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University

The Great Wall of China is not visible to the naked eye from space, even in low-earth orbit, according to NASA. Even though the wall is very long, it is also very thin, making it essentially invisible. In fact, no man-made objects are visible from space by the naked eye, according to astronauts. The earth is a very big place and human-sized objects are miniscule by comparison. With the help of zoom lenses, cameras in space can see much finer detail than human eyes. However, due to its thinness, the Great Wall of China is not the easiest man-made object for a camera in space to spot. If you slowly zoom in using a space camera, the Houston airport, for instance, is visible long before the Great Wall of China. Major highways radiating out like spokes from large cities are typically the most visible structures from space for a camera. This is because valleys are typically blasted through the hills to make way for the straight highways.

Topics: Great Wall of China, satellite, visible from space