The Sciences

Observer

By Stephen L Antczak and Amy EckertDec 3, 2004 6:00 AM

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WINSOME TELESCOPE

The 3.5-meter (137-inch) WIYN on Kitt Peak near Tucson in Arizona is the newest of 27 telescopes on the mountain and collects some of the world’s sharpest images, despite its relatively small primary mirror.

OWNERSHIP

The acronym WIYN stands for the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatory (NOAO). WIYN is the first public-private telescope collaboration. The universities put up most of the money to build the telescope; NOAO provides most of the operating money.

THERMAL CONTROL

Even slight temperature variations can distort images—one human’s heat output (about 100 watts) is more than enough to ruin results. Most of the dome can be opened at night so that the telescope and the observatory floor remain in sync with ambient temperatures. The base of the primary mirror is hollow. Air pumped through it keeps the glass within .5 degree Fahrenheit of the outside temperature.

MOUNT

The telescope is balanced on a platform that weighs a mere 36 tons. By contrast, the four-meter Mayall telescope a few blocks away weighs 375 tons because it has an equatorial mount aligned with Earth’s axis of rotation. WIYN uses a computer-controlled altitude-azimuth mount that can constantly change aim to follow an object through the sky. The scope is so finely balanced that a child can move it.

SHAPE-SHIFTING

The primary mirror’s curvature can be changed to offset distortions caused by temperature and gravity. Sixty-six computer-controlled rods filled with transmission fluid can each push with a force of 250 pounds against the mirror.

LIGHT

The telescope has three mirrors—a primary (spun melted glass that was molded onto a honeycomb back to save weight), a secondary, and a tertiary. It also has a collection of optional lenses. Each reflection off a mirror results in a loss of about 8 percent of the photons coming into the dome. The primary mirror must be removed and realuminized every other year to maintain the telescope’s image brightness and overall quality.

TURNS

Observing time on the telescope is allocated by investment. NOAO gets 40 percent of the time to dole out, Wisconsin gets 26 percent, and Indiana and Yale each get 17 percent. Two nights a month are allocated to maintenance and improvements during times when the moon is full and viewing is dismal. Any astronomer assigned time on the telescope can operate it remotely through the Internet from the Yale, Wisconsin, or Indiana campuses.

IMAGES

WIYN’s specialty is a high-quality wide-field (1 degree) view. Custom instrumentation is the key. Fiber optics allow simultaneous spectrographic readings of as many as 100 objects in the field of view; a fourth correcting mirror rapidly tips and tilts back and forth to cancel out image “wiggling” caused by turbulence in Earth’s atmosphere; new CCD image receptors can tip and tilt electronically. Engineers are at work on a larger, higher-quality CCD camera.

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