国产av不卡一区二区_欧美xxxx做受欧美_成年人看的毛片_亚洲第一天堂在线观看_亚洲午夜精品久久久中文影院av_8x8ⅹ国产精品一区二区二区_久久精品国产sm调教网站演员_亚洲av综合色区无码一二三区_成人免费激情视频_国产九九九视频

Spotting Great Wall from space IS possible
By Raymond Zhou and Ravi Shankar (China Daily)
Updated: 2005-04-19 00:04

First, the good news: The Great Wall of China can, indeed, be seen from outer space with the naked eye.

So education officials, who fretted about changing textbooks - which have long held that the Great Wall and the dykes in the Netherlands were the only man-made structures visible from space - can breathe easy. 

This shot of the Badaling section of the Great Wall was taken by space station astronaut Leroy Chiao on the morning of February 20 when he flew over Beijing at an altitude of 360 kilometres. The photograph, the first ever released by Chiao, was studied by Professor Wei Chengjie, an expert in remote sensing, who added the markings and toned down the blue colour so that it closer resembles the view one would have from an aeroplane.

Yang Liwei, the nation's first spaceman, disappointed a lot of Chinese when he said he did not see the wall during his orbit of less than 24 hours in October 2003, prompting calls for revisions in textbooks.

But there is a rider: There are many, many structures which can also be seen, such as the Pyramids of Egypt, airports, highways - and even Beijing's Third Ring Road.

Apparently, it requires an atmospheric "perfect storm" in outer space, defined as an altitude of about 350 kilometres and you have to be in the right place at the right time, amid the right conditions to spot a particular structure.

Chinese-American astronaut Leroy Chiao, who has been on three space flights and is currently coming to the end of his six-month stint on the joint US-Russian space station, has provided the first photographic evidence of sections of the Great Wall using commercially available equipment.

The photos have been authenticated by Professor Wei Chengjie of the Institute of Remote Sensing Applications at the Chinese Academy of Sciences.

However, Chiao is himself not certain: "It is hard to say whether or not I have seen it. That's because from our altitude, I cannot distinguish between the Wall and roads." He described his picture, taken on February 20, as a "region northwest of Beijing."

Spotting and photographing Chinese landmarks is Leroy Chiao's big hobby. All the equipment he uses is commercially available. There is no miracle telescope involved here. [Courtesy of Leroy Chiao]

While the layman might have difficulty in telling the highways, railways and mountain ridges apart, Wei easily identifies all of them.

Also, a group of snow-enhanced shots Chiao took in November last year have also been confirmed by the US National Aeronautical Space Agency as the "first verifiable views of the Great Wall of China ever identified in astronaut photography."

Chiao describes the near-impossible odds of spotting the wall or getting the perfect picture.

The space station orbits the earth every 90 minutes at an altitude of 360 kilometres and travels at a speed of 8 kilometres a second.

And the flight path is different for each orbit.

So the chances of shooting the Great Wall area are "maybe once every few days and only during daylight every three months."

Since late March, Chiao has had just one opportunity to fly over the Great Wall, but the weather was dodgy.

He has one last chance before he is scheduled to land in Kazakhstan on April 25 - and he will be keeping a sharp lookout.

Close

Today's Top News     Top China News
Tang: Japan failed trust of the Chinese people         Spotting Great Wall from space IS possible         NPC to discuss Basic Law interpretation         Invitation for second Taiwan party chief         Agreements pave way for China-Australia FTA         Bush says raising retirement age a possibility	Spotting Great Wall from space IS possible       Sino-ASEAN ties hit high prior to Hu's visit       Folk music makes it into the classroom       Cuban leader's trip seals two-pronged co-operation       Hainan gets legal adviser to help government       Germ warfare site bids for heritage status