‘Crown Jewels’ Installed on Hobby-Eberly Telescope

By Damond Benningfield

The “crown jewels” of the Hobby-Eberly Telescope (HET) upgrade — a set of four mirrors designed to sharpen the view to pinpoint precision — have been installed on the telescope. They soon will allow scientists to take their first views of the night sky with the refurbished telescope.

Together, the mirrors form the Wide-Field Corrector. The assembly sits at the top of the telescope, where it will capture light reflected from the primary mirror. Because of the mirror’s spherical surface, the image it produces is spread across a wide area. The corrector’s mirrors were carefully shaped to correct the view, focusing it to an area roughly the width of a human hair.

The mirrors also increase the telescope’s field of view, and they will allow scientists to use the 10 meters (33 feet) of the HET’s primary mirror. Originally, they could use no more than 9.2 meters during any single observation.

The corrector was built by the University of Arizona College of Optical Sciences in Tucson — a process that took five years. Engineers tested it on a sophisticated rig that used laser light, holograms, and computer algorithms to simulate the HET’s primary mirror.

Transporting the corrector from Tucson to McDonald Observatory — a trip of more than 500 miles — required careful planning and preparation as well. The corrector was sealed against dust and humidity and wrapped inside a thermal blanket to keep its temperature constant during the long drive, mounted atop shock-absorbing springs, and housed inside a custom-built shipping container. The package left Tucson on the evening of May 27, escorted by HET personnel and a University of Texas at Austin police car.

Final testing will start when the refurbished HET takes its first look at a star. After that, the scientific instruments will be tested and verified, allowing the HET to return to service.