Really Big Binoculars

Contributed by
Nov 6, 2005

Take a look at this:

Cool, huh? It's NGC 891, a relatively closeby edge-on spiral galaxy. OK, now keep that picture in mind for a sec while I digress.

A couple of years ago I bought a pair of binoculars at a star party. They're pretty nice, and I can see amazing stuff from my back yard (the Crab Nebula is a pretty easy target on a clear, moonless night). The problem is, they're so big that holding them is hard. The lenses are a full 7 centimeters across, and the binocs weigh about 1.5 kilos (3 pounds), so I can hardly keep them pointed. I bought a tripod to hold them up, which has helped a lot.

So I like them, and they're big enough to be impressive. At least, I used to think so. Then I heard about the LBT... the Large Binocular Telescope. Unlike your typical telescope which has one mirror, the LBT uses two mirrors to observe its targets. And these aren't small mirrors-- they are 8.4 meters across each-- the combined area is equivalent to a single mirror nearly 12 meters across. That's huge! But it's even better than that...

The mirrors are spaced several meters apart. By carefully combining the images produced by each mirror, details can be seen in an astronomical target that are far smaller than either mirror could do on its own. This technique is called interferometry, and it's been used in radio astronomy for decades. It's much harder at optical wavelengths, but we're clever, we apes. LBT will be able to use it routinely to see objects as small as 0.005 arcseconds across. By comparison, Hubble's resolution is about 0.1 arcseconds. That means LBT will be able to resolve an object just ten meters across if it were sitting on the Moon! Hubble's resolution limit at that distance is about 200 meters.

Currently, just one mirror is operating at LBT. But when you have a half million square centimeters of mirror, you can still do a lot. You can go pretty deep (seeing faint objects) and see lots of detail. OK, now go and look at that image of the galaxy NGC 891 again. That image is really deep, showing faint stars and galaxies. It was taken by the LBT, of course, in what's called the "first light" image (the first time the 'scope actually observes a target in the sky).

The LBT, with one mirror tied behind its back, took that image in just 5 minutes of observing! That's pretty impressive. Imagine what this thing can do when it's let loose on a target for an hour, or for five hours!

And when the second mirror comes online, it'll be more impressive. It'll be able to easily resolve Jupiter's moons, for example. It can look for planets orbiting other stars, and peer deep into the Universe to see what was happening a long time ago, near the time when the first stars formed.

When I was younger, this stuff was considered a pipe dream. Now it's a reality. Sometimes I wonder what could possibly be next.

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