The Great Wall of China is the only human-made object that can be seen from the moon or outer space.
You can see the Great Wall of China from the moon or outer space.
Hoax or Fact:
These are age old claims saying that the Great Wall of China is the only man-made object which is visible to the human naked eye even from the moon and outer space. This is simply NOT a fact.
It's a Popular Myth
The earliest known reference to this myth appears to be in a letter written by an English antiquary William Stukeley in 1754, who wrote "This mighty wall of four score miles in length (Hadrian's Wall) is only exceeded by the Chinese Wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the Moon." Similar claim was also mentioned by Henry Norman in 1895, stating "besides its age it enjoys the reputation of being the only work of human hands on the globe visible from the Moon." It appears like the prominent issue of "canals" on Mars in the late 19th century may have led to the belief that long, thin objects like the Great Wall of China were visible from space. Such a claim about the Great Wall also appears in Ripley's Believe It or Not! cartoon from May 1932, as "the mightiest work of man, the only one that would be visible to the human eye from the moon". The same claim was again raised in Richard Halliburton's 1938 book Second Book of Marvels. Since then this myth about the visibility of Great Chinese Wall from Space and Moon keeps resurfacing again and again.
The Actual Facts
The Great Wall of China is a 13,170 miles long defense system in North China spread across 15 Provinces, having a maximum 9.1 m (30 ft) wide wall, and is almost the same color as the soil surrounding it. From a low orbit of the earth, just like many artificial objects on earth are visible, like the highways, ships in the sea, railroads, cities, and some individual buildings, the same is the case with the Great Wall of China. But when you leave the earth's orbit and go to an altitude of more than a few thousand miles, no man-made objects will be visible to human eye. The same is explained by NASA:
China's Wall Less Great in View from Space
It has become a space-based myth. The Great Wall of China, frequently billed as the only man-made object visible from space, generally isn't, at least to the unaided eye in low Earth orbit. It certainly isn't visible from the Moon.
Considering the distance versus the width of the human iris and large telescopes, the optics of resolving power on moon was calculated. Taking into account the average distance of Moon from Earth as 384,393 km (238,851 mi), it was learnt that an object of reasonable contrast with its surroundings would be visible to the unaided human eye from moon only when it is 70 mi (110 km) or more in diameter (1 arc-minute). The Great Wall of China as seen from the Moon would be apparently of the size of a human hair viewed from 2 miles (3.2 km) away. This means, to see the Great Chinese Wall from Moon, we need to have 17,000 times better spatial resolution than the normal (20/20) vision we have. This is the reason why no lunar astronaut has ever claimed to have seen the Great Wall of China from the Moon. Such claims are just popular myth and a hoax.