ESA's Proba satellite here shows a winding segment of the 7240-km long Great Wall of China situated just northeast of Beijing
Editor's Note: This
image, it turns out, is not what we first reported. The European Space Agency
said May 19 that what they first declared to be the Great Wall is, instead,
a river. Story
The following Image of
the Day text appears as it was originally published:
"The Earth looked very beautiful from space, but
I did not see our Great Wall," lamented China's first astronaut, Yang Liwei,
after 21 hours in orbit last October. The comment triggered
a round of news stories that implied the structure could not be seen by any
astronaut, disappointing many Chinese who thought it was the only manmade
structure visible from space.
This photo, released yesterday, was taken by the European Space Agency's Proba
satellite on March 25. It shows a short stretch of the wall atop hills northeast
of Beijing. The wall is highlighted in the upper right. (The lower left of the
image is purposely washed out; it shows a stretch of engineered waterways called
the Da Yunhe, or Grand Canal, a marvel all its own.)
Sure, spotting the Great Wall of China from space is easy with the right telescope and camera. But why couldn't China's new hero see it? He just didn't have enough time or the right conditions, it would seem.
"In Earth's orbit at a height of 160 to 320 kilometers [100-200 miles], the Great Wall of China is indeed visible to the naked eye," says astronaut Eugene Cernan.
A low angle of sunlight casting long shadows can help.
"You can see the Great Wall," confirms astronaut Ed Lu, who was the science officer of Expedition Seven on the International Space Station. The station circles Earth higher than Yang Liwei's orbit.
The misconception is wrapped up in broader myths about what is and what is not visible from space. For the record: No manmade structures on Earth can be seen with the unaided astronaut's eye from the Moon. But many things -- highways, dams and even large vehicles -- are easily spotted from Earth-orbit with no optical aids. [What's Visible from Space]
-- Robert
Roy Britt
Credit: ESA/Proba
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