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Flying with the top down

Put a huge scope in an old 747, and you can almost see forever

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Right now, tucked away near the Bay Area in California, NASA scientists are building an entire astronomical observatory in a 747 airplane.

You may have noticed that astronomers tend to build their telescopes in the most out-of-the-way places. All major ground-based observatories are perched on top of desert mountains or on icy plateaus near the South Pole. The highest observatory on Earth is on the top of Mauna Kea in Hawaii. At 14,000 feet, astronomers working there routinely pass out from lack of oxygen. Why put yourself through that?

Astronomers aren't just trying to go to places with good weather, they're trying to go to places with comparatively little air.

If you're on Earth looking up at the stars, that light had to pass through the atmosphere to get to you. And if you're an astronomer who's trying to make very accurate measurements, all those air currents make the stars look wobbly and distorted, as if you were looking through the hot air rising above a barbecue. The problem is even worse than that, because air absorbs most of the radiation we get from space before it ever gets to us. Objects in space put out radiation in all forms of light, from gamma-rays and x-rays to microwaves and radio. Pretty much all of that gets taken out by our atmosphere, which is good for us, but bad for astronomy.

Cut to the early 1970s, with a bunch of astronomers trying to think out of the box. They wanted to build an observatory to look at infrared light coming from space. Infrared light is what we commonly think of as heat, and it's what most night-vision cameras "see." The reason you can see people in the dark is that these special cameras can image the heat coming from their bodies. Water vapor in our atmosphere absorbs nearly all infrared light from space, so for the longest time, this aspect of the universe was invisible. Even the highest mountains on Earth weren't above enough water vapor to see much infrared light.

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