Skip to main content
Science Journal hero astronomy with stamp

Eberly Impact: The Hobby-Eberly Telescope

9 March 2021
Eberly 30th anniversary banner

The Eberly Family Trust’s 1986 gift to the college provided critical support to design and construct the Hobby-Eberly Telescope (HET), then the world’s largest optical telescope. The HET, which took its first look at the universe in 1997, is now the world’s third-largest telescope and one of the premier instruments for finding and studying exoplanets, or planets outside our solar system.

The HET is also named after former Texas Lieutenant Governor William P. Hobby and results from a partnership between Penn State, the University of Texas at Austin, Stanford University, and two German universities, Ludwig-Maximilians-Universitaet Muenchen and Goerg-August-Universitaet Goettingen. It sits atop Mount Fowlkes as part of the University of Texas at Austin’s McDonald Observatory.

The HET opened the door to a new era in large-sized telescopes thanks to its unique and innovative design by Lawrence W. Ramsey and Daniel W. Weedman, which dramatically reduced the cost of the telescope and won the Discover Magazine Award for Technological Innovation in 1997. Its $20 million price tag was less than one-fourth of the cost of other telescopes in its size class. Soon after the HET’s construction, a telescope patterned after it—the South African Large Telescope (SALT)—was built in the southern hemisphere.

“The HET represented a different philosophy in building a large telescope, one which rests on a foundation of cost consciousness,” said Ramsey, who also served as the HET’s project scientist and later as the chairman of its board of directors. “At the core of the concept was constraining or eliminating the major cost drivers: the primary mirror and its support structure.”

Hobby Eberly Telescope at McDonald Observatory at night
Credit: Ethan Tweedie Photography 

Unlike other large telescopes, which track astronomical objects by moving their primary mirror, the HET’s primary mirror remains at a fixed angle during observations and instead sits on a rotating platform, maximizing sky coverage while minimizing cost. The primary mirror itself is composed of 91 identical segments, each about one meter across and weighing close to 250 pounds. Their small size and ease of handling and fabrication allowed the consortium to take advantage of low-cost/large-volume manufacturing techniques.

“The HET concept facilitates large extragalactic surveys, which are fundamental to understanding how the universe and its components work, and its design was tailored for spectroscopy and narrow-field imaging,” Ramsey said. “Spectra are the major tool in probing the physical conditions of remote astronomical objects and the only way to probe their kinematic properties.”

Since its debut, researchers from around the world have used the HET to publish more than 400 papers in scientific journals.

In April 2017, the HET was rededicated after undergoing multiple upgrades in preparation for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), which is a large international project to determine the nature of dark energy, the mysterious force that is accelerating the expansion of the universe. (For more on this, see “HETDEX and the ‘Quest for the Rest’”)

Later that year, the HET was outfitted with another spectrograph, the Habitable-Zone Planet Finder, which was designed by a team including Ramsey and Professor of Astronomy and Astrophysics Suvrath Mahadevan to improve detection of small exoplanets around small, cool stars called M dwarfs. 

“Over the past two decades, the HET has played an absolutely crucial role in increasing the international stature of our department, highlighting the scientific research performed at Penn State and assisting recruitment of outstanding students and faculty,” said Donald Schneider, head of Penn State’s Department of Astronomy and Astrophysics. “Penn State astronomers have used the HET to make many significant discoveries, ranging from identifying new exoplanets orbiting nearby stars to determining the properties of the most-distant known objects in the universe. Given the recent installation of the new innovative instrumentation, I have no doubt that the HET will produce a steady stream of exciting discoveries in the coming years.”