The dam of the largest power plant in the world “Three Gorges Dam” is visible from space with the naked eye. The Great Wall of China is not. But with the Egyptian pyramids, not everything is clear.
View from space
People often ask what human-made objects are visible from space. For example, it is widely claimed that the only such human-made structure is the Great Wall of China. But if you figure out what people actually saw from orbit, everything turns out to be much more complicated.
You need to start with what is considered space. Its generally recognized limit is the Pocket line, located at an altitude of 100 km from the surface of our planet. This is much higher than any aircraft flies, but still lower than the orbits of spacecraft. For example, the average altitude at which the International Space Station (ISS) is located is 415 km.
You also need to remember that “a person can see with the naked eye” and “person can observe from space” are different things. The capabilities of optical systems on observation satellites are many times greater than the capabilities of human vision. With their help, you can consider not only individual buildings, but also people and cars.
So, later in this article, “visible from orbit” will be understood as the ability to see something with the naked eye from the ISS.
Human-made objects visible from space
You need to start with those objects that are accurately visible from space. These include the Bingham Canyon mine in Utah, USA. It is the world’s largest open-pit mining site and the largest human-made object in the world. Copper is being dug here and in its search they have already plunged to a depth of 1200 m.
Bingham Canyon has a length of 7.7 km and a maximum width of 4 km. It is not surprising that it is regularly observed by astronauts on board the ISS.
Another object that can be easily seen from orbit is the dam of the world’s largest power plant “Three Gorges Dam”. It is located in China on the Yangtze River, 185 m high and 2 km long. But the artificial archipelago of Palm Jumeirah, according to NASA reports, is clearly visible from the Pocket line, but individual islands from the ISS can only be seen with a powerful lens.
Human-made objects that are not visible well
Some human-made objects on the surface of the Earth can not always be seen. These include, for example, large autobahns. But they can be observed with the naked eye. For example, Canadian astronaut Chris Hadfield managed to observe them at one time.
But there is no consensus among astronauts about the possibility of observing the pyramids at Giza. American astronaut Leroy Chiao said that at least two of the greatest he managed to observe the perfect weather as two tiny dots. But Briton Tim Peake does not agree with him. According to him, giant 150-meter buildings can only be seen with a powerful lens.
Objects that are not visible
Finally, there are numerous objects that are not visible to the naked eye from orbit. These include the Great Wall of China. The already mentioned Leroy Chiao photographed it from orbit, but by his own admission it is impossible to see it in the photo. It’s too narrow for that, and the surrounding terrain is too colorful.
It is also almost impossible to consider individual buildings in cities. The human settlements are clearly visible to the naked eye as large gray spots. But to see even individual broad avenues in them is a very difficult task.
According to www.space.com
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