Viewing Earth: How Much can be Seen from Space?
Even when the shuttle flies regularly, there is still a very limited number of humans who have had the privilege to see our home from space. Fortunately the shuttle and the International Space Station astronauts have returned a myriad of images of our home planet. Everyone knows that we can see the continents and oceans and frozen Arctic and Antarctic ice sheets, but what man made objects can be seen from space?
Many people believe that the Great Wall of China is the only man made object which can be seen from the shuttle or space station. The surprising truth about that is that unless the astronauts know exactly where to look, it is very difficult to spot. There are portions of the wall not even visible from Earth. They have long since been buried by sand, perhaps for centuries. NASA has used space-based radar to help map out these unseen stretches of the wall. Ed Lu, science officer for the recently returned Expedition Seven crew on the ISS (International Space Station) spent time looking for the Great Wall but had to battle clouds and haze.
Though Ed Lu never did get a really good picture of the Great Wall of China, he was nevertheless amazed at just how much else he could see from space, things that were much easier to see than the wall!
One of Ed Lu's favorite things to view were the great Egyptian pyramids at Giza. Though a bit tough to pick out with unaided eyes, they are easily visible with binoculars. The largest pyramid is 745 feet (227 meters) wide and 449 feet (137 meters) tall. The pyramids were photographed with a simple digital camera and high powered lenses.
Cities are easily distinguishable from surrounding countryside by both shuttle astronauts in an Earth orbit 135 miles (217 kilometers) high. They are just as visible on the space station which is in a higher orbit, circling the planet at 250 miles (400 kilometers). Using binoculars, the astronauts can see roads, airports, damn and even large vehicles. Harbors and even large ships and tankers can be seen on the oceans.
Astronauts can see things in Earth's atmosphere as well. Ed Lu watched for contrails from airplanes and could sometimes see the sunlight glint off the airplane itself. And just above the atmosphere, in various orbits, there are countless satellites which the astronauts would occasionally see go by.
As you get farther away from Earth, what you can see on our planet diminishes. From their vantage point on the Moon, Apollo astronauts could not make out any man made features on the planet. They could make out oceans and land masses but not much more. Further out, one sees even less. Should humans stand on Mars one day, and look for their home planet, Earth would appear as no more than a tiny blue dot, a bright "star" in the Martian night time sky. Even further out, from the realm of Pluto, the most distant planet, Earth cannot be seen. From here, the distant reaches of the Solar System, even the Sun appears as only a very bright star in the inky black of space.
If you would like to explore Earth from space, please visit the Visible Earth website run by NASA. http://visibleearth.nasa.gov/
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Kathy Miles, Author, and Chuck Peters, Systems Administrator
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