China's Wall Less Great in View from Space

May 10, 2005
China's Wall Less Great in View from Space

It has become a space-based myth. The Great Wall of China, frequently billed as the only man-made object visible from space, generally isn't, at least to the unaided eye in low Earth orbit. It certainly isn't visible from the Moon.
You can, though, see a lot of other results of human activity.
The visible wall theory was shaken after China's own astronaut, Yang Liwei, said he couldn’t see the historic structure. There was even talk about rewriting textbooks that espouse the theory, a formidable task in the Earth’s most populous nation.

Image: This photo of central Inner Mongolia, about 200 miles north of Beijing, was taken on Nov. 24, 2004, from the International Space Station. The yellow arrow points to an estimated location of 42.5N 117.4E where the wall is visible. The red arrows point to other visible sections of the wall. Credit: NASA.

The issue surfaced again after photos taken by Leroy Chiao from the International Space Station were determined to show small sections of the wall in Inner Mongolia about 200 miles north of Beijing.

Taken with a 180mm lens and a digital camera last Nov. 24, it was the first confirmed photo of the wall. A subsequent Chiao photo, taken Feb. 20 with a 400mm lens, may also show the wall.

The photos by Chiao, commander and NASA ISS science officer of the 10th Station crew, were greeted with relief and rejoicing by the Chinese. One was displayed prominently in the nation's newspapers. Chiao himself said he didn't see the wall, and wasn't sure if the picture showed it.

Kamlesh P. Lulla, NASA's chief scientist for Earth observation at Johnson Space Center in Houston, directs observation science activities from the Space Shuttle and the International Space Station. He says that generally the Great Wall is hard to see and hard to photograph, because the material from which it is made is about the same color and texture as the area surrounding it.

"The interpretation of this (Nov. 24) ISS photo," Lulla said, "seems to be good. It appears that the right set of conditions must have occurred for this photograph to capture the small segment of the wall." It was a sunny day and a recent snowfall had helped make the wall more visible.

The theory that the wall could be seen from the Moon dates back to at least 1938. It was repeated and grew until astronauts landed on the lunar surface.

"The only thing you can see from the Moon is a beautiful sphere, mostly white, some blue and patches of yellow, and every once in a while some green vegetation," said Alan Bean, Apollo 12 astronaut. "No man-made object is visible at this scale."

From space you can see a lot of things people have made, Lulla said. Perhaps most visible from low Earth orbit are cities at night. Cities can be seen during the day too, as can major roadways and bridges, airports, dams and reservoirs.

Of the wall visibility theories, Lulla said: "A lot has been said and written about how visible the wall is. In fact, it is very, very difficult to distinguish the Great Wall of China in astronaut photography, because the materials that were used in the wall are similar in color and texture to the materials of the land surrounding the wall -- the dirt."

It's questionable whether you can see it with the unaided eye from space. "The shape, the age of the structure, the resolution of the camera, the condition of the atmosphere -- all these factors affect the ability to detect an object from space." But, he added, "you can see the wall in radar images taken from space."

Source: NASA (by John Ira Petty)

Explore further: Image: The colors of sunset over the ISS

add to favorites email to friend print save as pdf

Related Stories

Researchers study fluctuations in solar radiation

Mar 18, 2015

The Sun is the Earth's principal source of energy and climate driver. Yet sometimes it sends more light to the Earth than other times. Astronomers working with Natalie Krivova at the Max Planck Institute ...

Image: Optical bench of LISA Pathfinder

Mar 12, 2015

An intimate view of a key part of the payload of ESA's LISA Pathfinder satellite, which will be the 'stillest' ever flown in space – in fact, the distant-orbiting spacecraft is set to become the single ...

A grand extravaganza of new stars

Mar 11, 2015

This dramatic landscape in the southern constellation of Ara (The Altar) is a treasure trove of celestial objects. Star clusters, emission nebulae and active star-forming regions are just some of the riches ...

Carina Nebula survey reveals details of star formation

Mar 09, 2015

A new Rice University-led survey of one of the most active star-forming regions in the galactic neighborhood is helping astronomers better understand the processes that may have contributed to the formation ...

Recommended for you

Russian, American ready for a year in space

16 minutes ago

The Russian astronaut heading off for a year in space says he'll miss the natural landscapes on Earth. His American counterpart jokes he won't miss his twin brother.

Galaxy clusters collide—dark matter still a mystery

5 hours ago

When galaxy clusters collide, their dark matters pass through each other, with very little interaction. Deepening the mystery, a study by scientists at EPFL and the University of Edinburgh challenges the ...

Using 19th century technology to time travel to the stars

10 hours ago

In the late 19th century, astronomers developed the technique of capturing telescopic images of stars and galaxies on glass photographic plates. This allowed them to study the night sky in detail. Over 500,000 ...

Image: The colors of sunset over the ISS

12 hours ago

ESA astronaut Samantha Cristoforetti took these images from the International Space Station during her six-month mission. The Progress cargo ship and Soyuz crew spacecraft reflect sunlight as our star sets ...

Feud on Earth but peace in space for US and Russia

15 hours ago

Hundreds of kilometres below on Earth, their governments are locked in a standoff over Ukraine—but up in space, Russian cosmonauts and American astronauts are still working together side by side.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.