double interferometer for visual astrometry

But even GPS satellites need a frame of reference from which they determine their own positions and develop their vaunted accuracy. In these days of global-positioning satellites, it may seem strange to think in terms of celestial navigation, Dr. The Naval Research Laboratory is also using the interferometer to study the distorting effects of Earth's atmosphere on light passing through it. In addition to the six movable mirrors, the facility hosts four more dedicated to astrometry or star-mapping. Much of the demand for this precision comes from the US Navy, which is charged with accurately measuring the positions of stars for navigation.

'If you could turn the array on its side and look at the San Francisco peaks' some 20 miles away, 'you could measure the diameter of a mouse's eyelash' on the summit of the tallest peak, enthuses Nathaniel White, a senior astronomer at the Lowell Observatory in Flagstaff who heads the NPOI development effort. The spacing of the array gives the facility the resolving power of a mirror 437 meters across, far surpassing the resolution of any single ground-based telescope. But when it comes to ground-based telescopes distinguishing two tightly-spaced objects, the NPOI can't be beat - at least not yet. The light-capturing mirrors at Keck are 10 meters across, compared with 50 centimeters for the NPOI. The array is decidedly modest compared with behemoth 'light buckets' such as the twin Keck telescopes in Hawaii. To accomplish this, the facility uses a technique called interferometry, in which light from the six widely spaced mirrors is gathered and combined to yield images of astronomical objects. And they've given detailed shape to shells of hot gas that old stars are ejecting before they go through their final death throes. They've mapped brightness variations across the surface of stars, leading to deeper insights into the stars' properties. The team expects to generate its first images in 2007.Īlthough the NPOI is still a work in progress, astronomers using it have discovered that familiar stars thought to be lone suns in the night sky actually are double-star systems. Earlier this month, Magdalena Ridge project officials signed a contract for the first of 10 telescopes that will dot the site. And the lessons the development team learns here are expected to benefit a similar but larger array planned for New Mexico's Magdalena Ridge, near Socorro. The array, dubbed the Navy Prototype Optical Interferometer (NPOI), is already yielding insights into nearby stars. The mesa is home to a unique array of telescopic 'eyes' - light-gathering mirrors that allow astronomers to study the surfaces of stars, search for extrasolar planets, and map positions of stars with high precision. On a broad mesa 12 miles southeast of Flagstaff, Ariz., astronomers are testing the notion that when measuring some of the brightest stars in the sky, six eyes are better than one.

Double interferometer for visual astrometry