That depends on what is meant by “seen” and “space” because the definitions of each determine whether or not the Great Wall of China can be seen from the heavens above.

First, let’s look at whether the Great Wall of China be seen by the unaided eye from space.  If we consider “space” to be a low Earth orbit–90 miles to 300 miles–it is possible for the Great Wall of China to be seen with the unaided eye… barely. Visibility of the Wall from this distance highly depends on ideal weather and lighting conditions.  The angle of the sun and the shadows produced by the Wall play a role in the visibility of the structure due to the fact that the eye most easily detects contrasting colors, especially from a distance. Visibility also depends on a person’s eyesight and whether or not he/she knows exactly where to look. Even then, only sections of the Wall may be visible. Since the Wall is made from stone, rock, and packed earth, it is similar in color to the soil surrounding it. Therefore, the structure can be extremely difficult to distinguish from its surroundings if searching for from space.

Since the Wall is very difficult to see from this distance, and because it is not the only landmark visible from within a low Earth orbit, it is easy for astronauts to mistake it for something else.  For instance, several astronauts claimed to have seen the Wall from Earth’s orbit, but it was later determined that what they actually saw was a river or the Grand Canal of China. So, yes, under perfect conditions, parts of the Great Wall of China are visible from a low Earth orbit, but it’s extremely difficult to distinguish and you need great eyesight. So practically speaking for most people and in most conditions the answers is no, but technically speaking, yes.

Obviously, if the idea of seeing the Great Wall of China from space is not limited to the unaided human eye, and a person uses the assistance of some sort of telescopic lens (binoculars/camera/satellite/etc.), then the likelihood of seeing the Wall from within a low Earth’s orbit, increases dramatically.

Now, if we consider space to mean a distance greater than the Earth’s orbit, like from the Moon, the answer for whether or not the Great Wall of China can be seen from space with the naked eye changes to a definitive “no”, despite what was often reported in the early 20th century. Since the Wall is barely visible from a low Earth orbit of 90 to 300 miles and the moon is located more than 225,000 miles from the Earth, it is impossible to see the Great Wall of China with the unaided eye from this distance. Some say viewing the Wall from the moon is like trying to see a single hair from two miles away. Astronaut Alan Bean is quoted as saying: “The only thing you can see from the moon is a beautiful sphere, mostly white, some blue, patches of yellow, and every once in a while some green vegetation. No man-made object is visible on this scale. In fact, when first leaving Earth’s orbit and only a few thousand miles away, no man-made object is visible at that point either.”

For many years before humans actually went to space, people believed the Great Wall of China was visible from space and that it was the only man-made structure visible from within a low Earth orbit. The origins of the myth are a little sketchy to determine, but one of the most notable sources supporting this theory was Richard Halliburton’s book, Second Book of Marvels – The Orient. The book was published in 1938 and stated: “Astronomers say that the Great Wall is the only man-made thing on our planet visible to the human eye from the moon.” Another source that supported the theory was Henry Norman’s, The People and the Politics of the Far East, from 1904: “Besides its age [the Great Wall of China] enjoys the reputation of being the only work of human hands on the globe visible from the moon.”

Considering the monumental event of sending the first person into space didn’t occur until 1961, no one could actually attest to whether or not the Wall could be seen from space before this, and people probably shouldn’t have accepted the theory so easily. However, given the size of the Great Wall of China (5,500 miles long, though with gaps, and 15-30 feet wide), it was probably easy for people to imagine such a large and significant structure being visible from hundreds and thousands of miles above Earth’s surface.  But once people started actually going to space and started searching for it, the myth was proved more or less false unless blessed by ideal conditions and eyesight.

Bonus Facts:

• In Chinese, the Great Wall of China is called “Wan-Li Qang-Qeng” meaning 10,000-Li Long Wall.
• The Great Wall of China is not actually one great wall like one might think, given its name. It is actually sections of individual walls joined together over time. The first sections of the wall were constructed during the Qin Dynasty between 221-206 BC. Through time, more sections of wall were built until they connected to form the Great Wall of China.
• The Great Wall of China was originally built to defend the Celestial Empire from enemies.
• The Great Wall of China is approximately 5,500 miles long, spanning from Shanhaiguan in east China to Lop Lake in west China. It consists of 3,890 miles of actual wall sections, 224 miles of trenches, and 1,387 miles of nature’s defenses including hills and rivers.
• During the next 20 years, more than 37 miles of the Wall is expected to erode away due to sandstorms in the Gansu province. Sections of the wall built from mud are more likely to erode than sections built from brick and stone.
• Rumor has it that nearly one million people lost their lives building the Wall.
• China has long prided itself on the supposed truth of the myth that the Wall can be seen from space. When Yang Liwei, the first Chinese person in space, stated he did not see the Wall in his 21.5 hour trip to space in 2003 when he orbited the Earth, China’s Ministry of Education decided to revise elementary school textbooks to remove the inaccurate information.