Building the world’s highest-resolution telescope
Ars Technica said:If Lowell Observatory’s Gerard van Belle gets his way, you’ll soon be watching an exoplanet cross the face of its star, hundreds of light-years from the Earth. He can’t show you that right now, but he should be able to when the new mirrors are installed at the Navy Precision Optical Interferometer in northern Arizona. They're arriving now and should soon start collecting starlight—and making it the highest-resolution optical telescope in the world.
Van Belle recently showed Ars around the gigantic instrument, which bears almost no resemblance to what a non-astronomer pictures when they hear the word “telescope." There are a couple of more traditional telescopes in dome-topped silos on site, including one built in 1920s in Ohio, where it spent the first few decades of its life.
Going big
The best way to improve imagery on these traditional scopes is to increase the diameter of the mirror catching light. But this has its limits—perfect mirrors can only be built so large.
The Keck Telescopes in Hawaii pushed the boundary by constructing a 10-meter mirror made of many smaller hexagonal mirrors arranged together. The Keck works because the only requirement for a telescope, van Belle explained, is that every ray of celestial light must travel exactly the same distance, even as it strikes the telescope's primary mirror, bounces off the smaller secondary mirror at the telescope’s snout, and arrives at the camera. No matter where light hits the hardware, every possible bouncing path must be the same length to within 50 nanometers—just one-thousandth the width of a human hair.
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But what is this telescope used for, you ask? The US Navy’s interest in this facility is in cataloging the positions of objects very precisely. While naval ships aren’t exactly following the North Star anymore, the world’s GPS navigation still depends on the stars, in part. Stars define the reference frame used to pinpoint the position of GPS satellites so that their signals can tell you exactly where you are.
And astronomers have taken advantage of the Navy's interests. Scientists at the Lowell Observatory have used this telescope to study the surfaces of nearby stars, for example. And with new mirrors comes new possibilities. “The thing that I really want to do, that would be just, kind of mind-blowing…” van Belle says with a grin. “We’re finding more and more planets around other stars, and some of them line up so they pass between the host and us, and we could actually make a movie of the shadow of another world as it goes in front of its host. It’s not quite imaging the surface of the planet, but you know, you’re basically seeing ‘not-planet’, which is kind of cool.”
They’ll also be able to push further into still-forming stellar systems of planets. Astronomers have imaged some of these rotating disks of dust and clumping baby planets, but we can’t make out too many details. At the wavelength used by these telescopes, we can really only see the cold outer reaches of these disks. With the new, larger mirrors, van Belle and his colleagues should be able to see into the warmer portions of the disk where liquid water could exist and planets could be forming.
This is, after all, how the game is played in astronomy: build a better telescope and see the next level of things you’d only dreamed of.
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