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4/12/04 (lplarizona ) Will you become extinct?

Use this site to calculate "the seismic, blast wave, and thermal effects of an impact as well as the size of the crater produced by the impact."


3/12/2004: Earth from Space: (Yahoo) We grew up thinking you could see the Great Wall of China from space. This is a myth. The myth was shattered when Chinese astronauts Yang Liwei returned from a 21 1/2-hour space flight. Textbooks will have be rewritten according to a story that just came out today.

"The wall stretches thousands of miles across northern China but is only a few yards wide, making it impossible to see from space."

I found it interesting that ABCnews said, "like many astronauts, he is not very talkative." His admission about not being able to see the Wall is interesting because at least one US astronaut is on record as saying you CAN see it.

If the Great Wall can't be seen by humans, it can certainly be seen by cameras in space. With a camera you can also see the pyramids from space. According to Space.com "Shuttle astronauts can see highways, airports, dams and even large vehicles from an Earth orbit that is about 135 miles (217 kilometers) high. Cities are clearly distinct from surrounding countryside, and that's true even from the higher perch of the International Space Station, which circles the planet at about 250 miles (400 kilometers) up".

"You can see an awful lot from space," says astronaut Ed Lu, the science officer of Expedition Seven aboard the station. "You can see the pyramids from space, especially with a pair of binoculars. They are a little difficult to pick out with just your eyes." The October 6, 2003 article also asks about the Great Wall of China. "You can see the Great Wall," Lu says. But it's less visible than a lot of other objects. And you have to know where to look." Have both astronaughts really been to space? Does one have super vision? Perhaps you can only see the Great Wall of China from space if you are not Chinese? May be the Chinese didn't send Yang Liwei up with binoculars.

"Yang's flight aboard a Shenzhou 5 was reported to range from 125 miles (200 kilometers) above Earth about 220 miles (350 kilometers). The space station is roughly 250 miles (400 kilometers) high." Space.com says, "The Great Wall of China is visible from Earth orbit, too. Yang just didn't see it." Interesting how different the various stories are on this.

Is it possible to see something a few yards wide at a distance of 250 miles? The Wall's width averages from 15 to 25 feet, with about a 13-foot wide roadway on top. I agree with Yang Liwei, and here is why: Take a look at a 15 foot object seen at 500 feet. (I did this for a mini-article on a giant bird seen some time ago.) Now consider that 250 miles is one million three hundred and twenty thousand feet. ( 1,320,000 feet ). The Wall is very long but it is also stationary in comparison to the background. With all due respect, I think Ed Lu and space.com are dreaming on this one. Try it yourself. Pick something 15 feet across on a hill and see if you can drive 10 miles from it and still see it. Then try 50 miles. I'll try to do some experiments this weekend.

 

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