Hobby-Eberly Telescope
Encyclopedia
The Hobby-Eberly Telescope is a 9.2-meter (30-foot) aperture
telescope
located at the McDonald Observatory
. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs. For instance, the telescope mirror itself does not move to track the night sky; instead, the instruments at the focus are moved across the face of the unmoving mirror, allowing a single target to be tracked for up to two hours. The primary mirror consists of 91 hexagonal elements, which is less expensive than a single large primary. The telescope is named for former Texas Lieutenant-Governor Bill Hobby
and for Robert E. Eberly
, a Penn State benefactor. Although the main mirror itself is fixed at 55 degrees angle, the telescope can rotate around its base, and the secondary can move;this allows access to about 70-81% of the sky at its location.
Three instruments are available to analyze the light from the targets. All three instruments are spectrograph
s. The instruments work at high, medium and low spectral resolution. The low-resolution spectrograph is housed at the prime focus, while the medium and high-resolution spectrographs reside in the basement and the light is fed into them via a fiber-optic cable.
Since achieving first light in 1996, the telescope has been used for a wide variety of studies ranging from our Solar System to stars in our galaxy and studies of other galaxies. The telescope has been used successfully to find planet
s orbiting around other stars by measuring radial velocities as precisely as 1 m/s. Using the low-resolution spectrograph, the telescope has been used to identify Type Ia supernova
e to measure the acceleration of the universe. The telescope has also been used to measure the rotation of individual galaxies. The telescope was upgraded for and took part in HETDEX.
The Hobby-Eberly Telescope is operated by The University of Texas McDonald Observatory for a consortium of institutions which includes The University of Texas at Austin
, Pennsylvania State University
, Stanford University
, Ludwig Maximilians University of Munich
, and Georg August University of Göttingen.
The physical main reflector mirror is larger than 9.2 meters; it is actually about 11 m by 9.8 m. However, the usable optical aperture at any given time is 9.2 m. The mirror itself is composed of 91 hexagonal segments, a segmented mirror
design like the Keck telescopes
. Updates to the telescope increased its field of view
from 4 arcminutes to 22 arcminutes (a full moon is 30 arcminutes for comparison). The telescope mirrors are aligned within a fraction of a wavelength of visible light by actuators under each segment. The tower next to the telescope, called the Center of Curvature Alignment Sensor Tower (CCAS), is used to calibrate the mirror segments. One of the advantages of this type, is that it was over 5 times more cost efficient for its aperture than a more traditional design.
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
located at the McDonald Observatory
McDonald Observatory
The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas...
. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs. For instance, the telescope mirror itself does not move to track the night sky; instead, the instruments at the focus are moved across the face of the unmoving mirror, allowing a single target to be tracked for up to two hours. The primary mirror consists of 91 hexagonal elements, which is less expensive than a single large primary. The telescope is named for former Texas Lieutenant-Governor Bill Hobby
William P. Hobby, Jr.
William Pettus “Bill” Hobby, Jr., is a Texas Democratic politician who served a record eighteen years as the 37th Lieutenant Governor...
and for Robert E. Eberly
Robert E. Eberly
Robert Edward Eberly , son of Orville and Ruth Eberly, served as Chairman of the Board of Eberly Natural Gas Company, an oil and natural gas exploration and production firm. He was also a director of Gallatin National Bank...
, a Penn State benefactor. Although the main mirror itself is fixed at 55 degrees angle, the telescope can rotate around its base, and the secondary can move;this allows access to about 70-81% of the sky at its location.
Three instruments are available to analyze the light from the targets. All three instruments are spectrograph
Spectrograph
A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
s. The instruments work at high, medium and low spectral resolution. The low-resolution spectrograph is housed at the prime focus, while the medium and high-resolution spectrographs reside in the basement and the light is fed into them via a fiber-optic cable.
Since achieving first light in 1996, the telescope has been used for a wide variety of studies ranging from our Solar System to stars in our galaxy and studies of other galaxies. The telescope has been used successfully to find planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s orbiting around other stars by measuring radial velocities as precisely as 1 m/s. Using the low-resolution spectrograph, the telescope has been used to identify Type Ia supernova
Type Ia supernova
A Type Ia supernova is a sub-category of supernovae, which in turn are a sub-category of cataclysmic variable stars, that results from the violent explosion of a white dwarf star. A white dwarf is the remnant of a star that has completed its normal life cycle and has ceased nuclear fusion...
e to measure the acceleration of the universe. The telescope has also been used to measure the rotation of individual galaxies. The telescope was upgraded for and took part in HETDEX.
The Hobby-Eberly Telescope is operated by The University of Texas McDonald Observatory for a consortium of institutions which includes The University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
, Pennsylvania State University
Pennsylvania State University
The Pennsylvania State University, commonly referred to as Penn State or PSU, is a public research university with campuses and facilities throughout the state of Pennsylvania, United States. Founded in 1855, the university has a threefold mission of teaching, research, and public service...
, Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
, Ludwig Maximilians University of Munich
Ludwig Maximilians University of Munich
The Ludwig Maximilian University of Munich , commonly known as the University of Munich or LMU, is a university in Munich, Germany...
, and Georg August University of Göttingen.
The physical main reflector mirror is larger than 9.2 meters; it is actually about 11 m by 9.8 m. However, the usable optical aperture at any given time is 9.2 m. The mirror itself is composed of 91 hexagonal segments, a segmented mirror
Segmented mirror
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric . They are used as objectives for large reflecting telescopes...
design like the Keck telescopes
Keck telescopes
The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of near the summit of Mauna Kea in Hawai'i. The primary mirrors of each of the two telescopes are in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio...
. Updates to the telescope increased its field of view
Field of view
The field of view is the extent of the observable world that is seen at any given moment....
from 4 arcminutes to 22 arcminutes (a full moon is 30 arcminutes for comparison). The telescope mirrors are aligned within a fraction of a wavelength of visible light by actuators under each segment. The tower next to the telescope, called the Center of Curvature Alignment Sensor Tower (CCAS), is used to calibrate the mirror segments. One of the advantages of this type, is that it was over 5 times more cost efficient for its aperture than a more traditional design.
External links
See also
- List of largest optical reflecting telescopes
- Southern African Large TelescopeSouthern African Large TelescopeThe Southern African Large Telescope is a 66m2 area optical telescope with a nominally 9.2 meter aperture but up to about 11.1m x ~9.8 m diameter aperture, and designed mainly for spectroscopy. It is located close to the town of Sutherland in the semi-desert region of the Karoo, South Africa...