Visibility from the moon of china wall

One of the earliest known references to this myth appears in a letter written in 1754 by the English antiquary William Stukeley. Stukeley wrote that, "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." The claim was also mentioned by Henry Norman in 1895 where he states "besides its age it enjoys the reputation of being the only work of human hands on the globe visible from the moon." The issue of "canals" on Mars was prominent in the late 19th century and may have led to the belief that long, thin objects were visible from space. The claim that the Great Wall is visible also appears in a 1932 Ripley's Believe it or Not cartoon and in Richard Halliburton's 1938 book Second Book of Marvels.
The claim the Great Wall is visible has been debunked many times, but is still ingrained in popular culture.The wall is a maximum 9.1 m (30 ft) wide, and is about the same color as the soil surrounding it. Based on the optics of resolving power (distance versus the width of the iris: a few millimeters for the human eye, meters for large telescopes) only an object of reasonable contrast to its surroundings which is 70 mi (110 km) or more in diameter (1 arc-minute) would be visible to the unaided eye from the moon, whose average distance from Earth is 384,393 km (238,851 mi). The apparent width of the Great Wall from the moon is the same as that of a human hair viewed from 2 miles away. To see the wall from the moon would require spatial resolution 17,000 times better than normal (20/20) vision Unsurprisingly, no lunar astronaut has ever claimed to have seen the Great Wall from the moon.

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