I have no proof but I also have no doubt that at some point in your childhood you were told that the Great Wall of China was the only human-built structure visible from space . This statement does not go back to my childhood or yours, it does not even go back to the first satellites capable of taking photos from hundreds or thousands of kilometers high. The earliest known reference to such a claim is from William Stukeley , an English physician and antiquarian, who mentioned in passing that the Great Wall could be visible from the Moon in a letter written in 1754 , more than 200 years before anyone could. go there to check it out. Now that we have gone to the Moon and we have photos taken from there, it is evident that no, the Great Wall of China is not visible from so far away.
Ok, from the Moon surely not, but what about from space? Well, all you have to do is go to your favorite mapping application, type “Great Wall of China” in the search engine and realize that it is technically visible from space . But with the satellites we have in orbit, a car or a garbage can and even a person can be seen. This is certainly not what Stukeley was referring to or what you imagine when you say something is “visible from space.” More precision will be needed. Let us then ask what is visible to a human in orbit with the naked eye . That is, without the help of binoculars, telescopes or cameras.
This is a photo taken from the International Space Station by astronaut Leroy Chiao in 2004. The photo was taken from an altitude of about 348 km and with a 180mm focal length lens. The lens of a camera has greater zoom the greater its focal length . Human vision is generally considered to be equivalent to a focal length of about 35mm, so we cannot consider the 180mm in Chiao’s photo as what we would see with the naked eye. For obvious reasons I cannot show you what he saw before taking the picture, without using the camera. But anyway, what exactly does the photo show? According to Stukeley it should be self-evident. A piece of the Great Wall of China is shown in the photo. Looking at this photo, we can then say that, without a doubt, the Great Wall of China would not be visible from space with the naked eye, because it would not even be visible magnified several times.
So what would be visible? Take the International Space Station as the most likely location for anyone who wants to spend some time in space , especially some time sightseeing and observing the Earth’s surface. The angular resolution of the human eye is about 1 minute of arc , or about 0.28 milliradians. That is, the apparent size of a soccer ball at a distance of about 750 meters. In addition, the International Space Station is located at an average height of about 400 km above the earth’s surface. With these two data it can be calculated that the minimum that a person with perfect vision, without clouds and good atmospheric conditions could distinguish would be an object of about 110 meters in diameter . For example, you would be able to see the Santiago Bernabeu stadium in Madrid. However this would be at the limit of his visual capacity and would be barely distinguishable. The following 5 buildings (or constructions or structures), unlike the Great Wall or a football stadium, would be visible. We will not take into account things like “the lights of a city at night” or “the deforestation of the Amazon”, which although clearly visible, are not comparable to the Great Wall of China.
Aerium, Germany
This 360-meter-long by 210-meter-wide structure was originally built as a hangar to build planes, but later changed owners and currently houses the Tropical Islands water park. This is one of the largest buildings (by volume) in the world and would undoubtedly be visible to the naked eye from space.
Masjid al-Haram Grand Mosque, Saudi Arabia
This mosque, located in the city of Mecca, is the most important in Islam for housing the Kaaba and is also the largest temple in the world and a place of obligatory pilgrimage for all Muslims. With its more than 500 meters in diameter and its white color, it would be visible from Earth orbit.
Artificial Islands, United Arab Emirates
This series of mega-constructions located on the coast of Dubai, in the United Arab Emirates, is so large that it houses residential areas, shopping centers and a multitude of hotels and resorts on its surface . They are not a building, but they are eminently artificial and, more importantly, highly visible from space.
Bingham copper mine, USA
This mine, located in the state of Utah, near Salt Lake City, is the largest excavation (in volume) ever made with a depth of almost 1000 m and a diameter of more than 4 km . Some 17 million tons of copper have been extracted from it and it is so large that numerous avalanches and rock falls have occurred during its history.
Campo de Dalias, Spain
The prize for the most visible human structure or group of human structures from space goes without a doubt to Campo de Dalías. In this region of the province of Almería, intensive agriculture under plastic has been practiced since the 1960s, that is, cultivation in greenhouses. Since the first greenhouse in the area was built in 1963, this practice has grown to occupy more than 200 km 2 , an area comparable to that of the island of El Hierro , distributed throughout the province, most of which are in this region. The fruit and vegetables grown in these greenhouses account for approximately half of all those sold from Andalusia and these crops are the main economic driver of the province. But all that is secondary, what matters to us here is that they are the most visible human construction from space.
It is truly a shame that the last three structures, to be in that position, have to have a considerable impact on the ecosystems of the area. With this article we do not intend to praise bad ecological practices, but only to dismantle a myth and give several alternatives and curious data.
