美国国家公共电台 NPR The Largest Digital Camera In The World Takes Shape（在线收听）

RACHEL MARTIN, HOST:

Astronomers are building the world's largest digital camera to capture images of the night sky. This thing is two stories tall, a scientific marvel. So of course NPR's science correspondent Joe Palca traveled to California to check it out.

JOE PALCA, BYLINE: A two-story-tall camera - I couldn't wait to see that. But when I got to the SLAC National Accelerator Laboratory where the camera is being put together, I got some bad news.

AARON ROODMAN: Right now every piece of the camera is under construction in various places.

PALCA: Aaron Roodman is the physicist at SLAC in charge of putting the camera together. He says the final assembly is still about two years away. But Roodman says even the small parts of the camera are astounding and worth a look. He offers to take me into the two-story-tall clean room they built at SLAC just for this project.

ROODMAN: Clean room procedures are pretty common for working with CCD cameras.

PALCA: You can't just walk into a clean room. You have to put on gloves, hats, booties and extremely clean white coveralls. Fully garbed, you look a bit like an Easter Bunny. This super-clean getup is necessary.

ROODMAN: A piece of dust on any of those surfaces we'll really notice. It will actually have a significant negative effect on the camera.

PALCA: Roodman points to a small box with cables coming out of it sitting on a lab bench.

ROODMAN: All by itself, this little unit is 144-megapixel camera.

PALCA: That's six times more megapixels than a high-end digital camera.

ROODMAN: So by itself, it's kind of a remarkable device.

PALCA: And there will be 21 of these boxes in the camera. Astronomers have big ambitions for this giant camera. It's going on a giant telescope being built in Chile called the Large Synoptic Survey Telescope. That telescope will be unlike any other. Instead of staring at a tiny patch of the sky and taking essentially one snapshot in time, the new telescope will take a panorama of every part of the sky. And it will do so over and over and over and over. The idea is to see what's moving or changing in the heavens.

ROODMAN: That could be everything from asteroids to variable stars to Supernova to maybe new phenomenon that we don't know about yet.

PALCA: Roodman is right to expect the unexpected. But don't ask him what that might be because he has no idea. That's the whole point. Now, for the camera to work properly and make sure all the stars it sees are in focus, everything in the camera has to be in exactly the right place. Roodman takes me to another lab on campus where they're working on that.

ROODMAN: This is a metrology lab. This is a place to measure...

PALCA: A what lab?

ROODMAN: Metrology.

PALCA: Metrology.

ROODMAN: Metrology.

PALCA: It's a new word on me.

ROODMAN: Metrology is the science of measuring things.

PALCA: Roodman says they have to measure where things are to within a twentieth of the thickness of a human hair, depending of course on how thick your hair is. Not all the preparation and testing of the camera is super high-tech.

At another test bench, some graduate students are trying to make sure that the interior of a dark box is completely dark. And they're having a problem blocking out the glare from some LED lights mounted near the box. Roodman suggests putting some black tape over the lights. Then he laughs.

ROODMAN: This is the beauty of experimental physics. On the one hand, (laughter) we want - I'm interested in studying the makeup of the universe. But for today, we got to make sure that the tape is blocking out all the light from some LEDs.

PALCA: Roodman expects by 2020, astronomers should be able to start using his camera to study the makeup of the universe, presumably without the need for black tape. Joe Palca, NPR News.

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