Is Great wall of China really visible from Space?

It's actually a very popular Space-based Myth.

We have all been told from our school times that the only man-made object visible from space is the Great Wall of China but it isn't, at least to our naked eyes from Earth's lower orbit. And its definitely not visible from Moon.

In fact, it was one of China's astronaut named Yang Liwei who confirmed that he couldn't see the wall from space and there were discussions about correcting textbooks that talked about this theory but with such large population of this nation, it was such a daunting task.

The Chinese were relieved and rejoiced when Leroy Chiao took the first confirmed photo of the wall from the International Space Station. It was taken with a digital camera that had a 180mm lens. However, Chiao himself wasn't sure if the picture showed the wall. He took another photo later with a 400 mm lens that may show some wall.

Kamlesh P. Lulla, NASA's chief scientist for Earth observation at Johnson Space Center in Houston, says that generally the Great Wall is hard to see and photograph, because its material blends it with its surrounding. Thus a sunny day and a recent snowfall helped Chiao capture a small segment of the wall from the ISS. 

There are few human activities that you can actually see from space especially cities at night. In fact, you can see Cities and its elements like roadways, bridges airports, dams etc.

Great Wall of China however is really difficult to see or capture due to its material matching the surroundings however it can be seen in images taken by a radar from space.