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Is the emphasis on the construction of very large ground-based telescopes (6-10 meters) at the expense of smaller telescopes (1-4 meters) a poor allocation of resources?

Viewpoint: Yes, the emphasis on the construction of large telescopes is a poor allocation of resources, as smaller telescopes offer accessibility and affordability that larger telescopes cannot match.

Viewpoint: No, the emphasis on the construction of large telescopes is not a poor allocation of resources; on the contrary, such large telescopes are indispensable to the research questions at the heart of modern astronomy.

At the time of its invention 400 years ago, the telescope was a crude and arcane instrument known to only a few brilliant scientists such as Galileo. Today, it is a commonplace item available in department stores for less than $100. Small department store telescopes, however, often carry misleading advertising in the form of huge print on the box proclaiming "Magnifies 880X!" This means that with the proper eyepiece in place, the telescope will magnify an image 880 times—but it is hardly the most relevant property of the instrument.

Telescopes are most usefully characterized by the diameter of their primary light-gathering optical element, whether a lens or mirror. This main optical element is the telescope's "light bucket," with which it collects light from distant objects. The size of this element is therefore the real indicator of a telescope's power, and when astronomers talk about the size of a telescope, they invariably are referring to this quantity.

A very small telescope (with a 50 mm [2 in] objective lens, for example) collects only a small amount of light. Such an instrument cannot be productively used at high magnification, because it does not collect enough light to produce a bright, magnified image. To observe distant, faint objects in detail, there is no substitute for a larger light-gathering area. Telescopes have therefore grown over the years from the small refractor used by Galileo to huge reflecting telescopes with light collecting areas 10 m (33 ft) in diameter or more.

The size of the telescope used for modern research in astronomy obviously depends on the science in question. Some projects can be carried out with 1-m (39-in) class telescopes—that is, telescopes with a primary mirror on the order of 1 m (39 in) in diameter. If the observations being carried out are primarily of bright objects, such a telescope is perfectly adequate. Because the area of a circular mirror increases as the square of the diameter, however, a 4-m (157-in) telescope collects 16 times as much light as a 1-m (39-in) telescope, enabling it to take observations of fainter objects, or to observe comparably bright objects 16 times as rapidly. In addition, larger telescopes can provide greater resolution—the ability to see fine detail—than smaller ones. A very simple example is that of imaging two very close stars, which in a small telescope might look like a single point of light, but which a large telescope would resolve as two separate points.

Because of these two reasons—ability to observe fainter objects, and the ability to see greater detail—increasingly large telescopes have figured prominently in cutting-edge astronomical discovery. When one is suddenly able to observe objects that could not be observed before, exciting science invariably results.

The catch, of course, is the price. The cost of a telescope does not increase proportionally to the diameter of its collecting area. A 50-mm telescope (i.e., with a lens roughly 2 inches in diameter) might be purchased for $70, but a 200-mm (8-in) telescope costs not $280, but closer to $1,000. Multiply the mirror diameter by two again (400 mm, or 16 in), and you'll spend at least $15,000, while a high-quality, computer controlled 16-in (41-cm) telescope can be purchased and installed for $75,000.

Continuing into the realm of large research-grade telescopes, the costs rise sharply. A modern 4-m (157-in) telescope has a primary mirror 80 times as large as the little 50-mm (2-in) telescope's, but such an instrument will cost $20 to $30 million to build. Finally, the cost of the gargantuan 8-10-m (315-394-in) class instruments can easily reach nine figures: $100,000,000 or more. As will be seen in the articles that follow, these telescopes are now beginning to exploit multiple, segmented mirrors to produce a large whole, interferometric techniques to achieve extremely high resolution, and adaptive optics to counteract the degrada tion of image quality that results as light traverses Earth's atmosphere. This technology is extremely expensive, and one of these large telescopes therefore costs about as much as three brand-new, fully functional Boeing 737s.

Such staggering expenses are typically much more than a single educational institution can afford. A university with an astronomy department wishing to build a large telescope frequently must join a consortium of institutions with similar interests, who can collectively come up with the entire sum. Adding more cooks to stir the proverbial pot adds the usual difficulties of administration and competing agendas, often putting projects behind schedule and over budget. In some cases, private foundations have spearheaded the construction of large new telescopes. And there are large telescopes available for use, on a competitive basis, at nationally funded observatories such as Kitt Peak near Tucson, Arizona. In any of these cases, there is a finite amount of money, and frequently the high cost of constructing and then running a large telescope have precluded the construction or maintenance of smaller facilities. The question naturally arises: if you can build one 10-m (394-in) telescope, or 100 1-m (39-in) telescopes, for about the same amount of money, which is the proper way to go?

Certainly a 10-m (394-in) telescope can carry out projects that are simply out of the reach of a 1-m (39-in) instrument. But this is not to say there is no longer any useful science to be done with smaller instruments. Large telescopes offer unparalleled light-gathering capability, but there are plenty of poorly understood aspects of our own Sun, from which we receive no shortage of light. Examples of fundamental problems in astronomy involving bright, easily observed objects abound. In the light of perennial budget limitations, what should we be doing? In the following articles, we will examine the tradeoffs between pushing the limits of ever-larger light buckets that peer to the edge of the observable Universe, and maintaining the small observatories that gather fundamental data about brighter or more nearby objects, at a small fraction of the cost.

—JEFFREY C. HALL

Viewpoint: Yes, the emphasis on the construction of large telescopes is a poor allocation of resources, as smaller telescopes offer accessibility and affordability that larger telescopes cannot match.

Many large, national observatories are retiring smaller ground-based telescopes in order to increase funding for larger ground-based telescopes. However, small telescopes can effectively work both alone and in conjunction with larger telescopes if they are adapted to specialized or dedicated projects. For this reason, the emphasis on the construction of large, ground-based telescopes (from 6-10 m) at the expense of smaller telescopes (from 1-4 m) is a poor allocation of resources. (Telescopes are typically compared to one another by the diameter of their primary mirror, which in this article will be measured in meters; one meter is approximately equal to 3.28 feet.)

Scientific Impact

The scientific impacts of the various sizes of telescopes are often compared on the basis of their contributions within the astronomical community. Chris R. Benn and Sebastian F. Sánchez of the Isaac Newton Group of Telescopes in Santa Cruz de La Palma, Spain, found that ground-based small telescopes, from 1-4 m, had a strong prevalence in their contributions to the 1,000 most-often-cited research papers and to the 452 astronomy papers published in Nature from 1991 to 1998.

One conclusion of the Benn-Sánchez study with regards to both large and small, ground-based telescopes was that their usefulness was proportional to their light-gathering area and approximately proportional to their cost. In other words, the smaller cost of building a small telescope is as well spent as the larger cost of building a large telescope, thus supporting the stance that telescopes in the 1-4 m category should continue to be built. Benn and Sánchez further concluded that small-and mid-size telescopes should not be deactivated to help pay for building larger new ones. They stated that "cutting-edge" advancements by the smaller class of telescopes support the continuing impact that small telescopes make in the scientific community.

Scientific Discovery

Gopal-Krishna and S. Barve, members of the Astronomy Society of India, stated in 1998 that after analyzing 51 astronomy papers published in Nature from 1993 to 1995 that were based on data from ground-based optical telescopes, 45% of the researchers solely used data from telescopes with mirror diameters less than 2.5 meters. The authors suggested that many of the leading scientific researches being performed within astronomy are still done by smaller-sized telescopes, further highlighting the essential role that these telescopes perform in astronomical research.

Current Trends

A 10-year review conducted at the end of the twentieth century of astronomy priorities by the National Research Council (NRC) barely mentioned the critical function of small telescopes in modern scientific research, a viewpoint held by many astronomers. The report, instead, focused on large projects such as a proposed 30-meter segmented-mirror telescope that would have a construction cost of at least $500 million for the United States and its international partners. Even though many astronomers hold a firm belief in the value of small telescopes, the unfortunate trend, as shown in the NRC study, is toward emphasizing the large telescope.

The National Optical Astronomy Observatories (NOAO) of Tucson, Arizona, recently transferred its 1-meter telescopes to private consortia of universities. NOAO, one of the largest astronomy-based organizations in the United States, provides U.S. research astronomers with access to ground-based telescopes that image in the optical-and-infrared (OIR) portions of the spectrum. The effect of such transfers is to remove smaller telescopes from access to the general astronomy research community.

Although small telescopes have not garnered the attention that larger telescopes have, and have moreover been removed from operations in favor of larger telescopes, there is continuing evidence that the leaders of some organizations realize that small telescopes are critical to robust astronomical research. As an example, consider the actions of the NOAO. It has been unable to maintain its expertise in all aspects of OIR astronomy due to budgetary constraints. This, in turn, has caused NOAO to limit its areas of concentration so that it can maintain its scientific leadership (as described previously, NOAO has shed its one-meter telescopes). As a result, NOAO's twin 8-meter Gemini telescopes were given its highest priority with respect to science, operations, and instrumentation. However, NOAO's second priority was to support its smaller telescopes (those from 2-4 meters) that show the best possible capabilities. NOAO stated that such smaller telescopes are essential in order to (1) support the Gemini program, (2) provide other national capabilities (such as projects within wavelength bands other than optical and infrared), and (3) support the scientific programs of its researchers and students. The NOAO will continue to technologically upgrade and maintain its remaining small telescopes with dedicated instruments (such as charge-coupled device [CCD] imagers) in order to fully support the activities of its astronomers and staff. Such activities go contrary to the widely held belief that only large telescopes should be built and maintained for the astronomical community.

NOAO will be forced to focus its attention on fewer tasks, but these critically selected tasks will involve telescopes of both small and large sizes in order to accomplish successful science projects in the most efficient way possible. Even though many other organizations are eliminating smaller telescopes, the NOAO is proving that small telescopes are important, even essential, to future astronomical research and development.

Specialty Purposes.

As an example of a specialty use for small telescopes, a new 3.5-meter WIYN telescope (owned and operated by the WIYN Consortium, consisting of the University of Wisconsin, Indiana University, Yale University, and the NOAO) at Kitt Peak National Observatory will complement the large Gemini North telescope in the areas of intermediate field-of-view, wide-field multi-object spectroscopy, high-resolution imaging, and near ultraviolet.

John Huchra of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, says that small telescopes can be very cost effective when used for projects that are not suitable for larger telescopes. Huchra states that in some cases small telescopes are assuming a more important role as they complement the work of larger telescopes. Indeed, Janet Mattei, director of the American Association of Variable Star Observers, in Cambridge, Massachusetts, stated that small telescopes are the "backbone" of astronomy even though they rarely make headline news.

Availability.

Astronomers realize that the availability of large telescopes may only be a few nights each month and that time is scheduled months or even up to a year in advance. So the smaller telescopes allow astronomers to fill their need for observation time, and to monitor rare celestial events or track the long-term behavior of astronomical objects.

Automation.

Fully automated small telescopes are frequently used to perform jobs that need to be done on a regular basis, and done more accurately than possible with human effort. These preprogrammed systems are designed, for instance, to automatically open the viewing dome when observational/recording conditions are appropriate. Alex Filippenko, an astronomer at the University of California, Berkeley, says that smaller, robotic telescopes, unlike large telescopes, are ideal for performing repetitive tasks that require many observational nights. Filippenko uses a 0.75-meter Katzman Automatic Imaging Telescope to find nearby supernovae. The telescope records images of several thousand galaxies, one by one, and then repeats its observations every three to five clear nights.

Another robotic small telescope system is the Robotic Optical Transient Search Experiment at Los Alamos National Laboratory, New Mexico. It uses small telescopes that can swivel quickly to any portion of the sky. Astronomers built the system to pursue the optical flashes associated with gamma ray bursts. Such quick response to random events is normally very difficult with large telescopes, because nearly all their observational time is already reserved.

Unattended automation of small telescopes, such as the two previously mentioned, has proven to be very effective in increasing the efficiency of observations and in reducing operational cost. However, the major motivating factor for automation of small telescopes is the new types of science that are permitted, which are otherwise unavailable under either conventional scheduling policies or large telescopes. Unattended automation has proven to be an effective operational style of smaller U.S. research telescopes.

Long-term Observations.

Greg Henry of Tennessee State University, Nashville, uses the Fair-born Observatory, located near the Mexican border in Arizona. Henry's observations illustrate a big advantage that small telescopes have over large telescopes. Small telescopes can be dedicated to performing long-term observations that watch for changes over time. Henry's four small telescopes are used to study long-term changes in the brightness of stars that are similar to the Sun. The results of studying those Sun-like stars can be used to understand how the Sun influences Earth's climate. Such observations would be impossible with large telescopes because observation time is constantly in demand by many researchers, and must be reserved months ahead. Henry states that he has gotten 50 to 100 years worth of data, which is much more than he could have gotten manually or with the infrequent use of large telescopes. Moreover, Henry asserts that the cost of obtaining his data was a small fraction of what he would have incurred had he used a large telescope.

As another example highlighting the advantages of small telescopes over large ones, astronomers are using worldwide networks to conduct continuous studies of specific stars. One such group of small telescopes is the Whole Earth Telescope project, directed by astronomer Steve Kawaler at Iowa State University, Ames. The network consists of more than 60 international astronomers located in 16 countries around the world (such as China, South Africa, Lithuania, and Brazil). The telescopes range from a 0.6-meter telescope in Hawaii to an almost 3-meter telescope in the Canary Islands. Studying dwarf stars around the clock, in order to predict what the Sun might become in a few billion years, is impossible for a single telescope because of Earth's rotation, and would be impractical for several large telescopes because such dedicated use for long periods of time is not practical for large, expensive telescopes. Instead, the strategy is to use numerous small telescopes from around the world to continuously observe the dwarf stars, and then send all the collected data to the projects' Iowa headquarters.

Education.

The 0.6-meter telescope on the campus of Wesleyan University, Middletown, Connecticut, contributes to astronomy education. Wesleyan is representative of smaller educational institutions with only a few astronomers and an emphasis on undergraduate education. Such institutions are important for producing astronomy applicants for graduate study. The value of this educational telescope is that it: (1) stimulates student interest in astronomy, (2) teaches undergraduate science using actual observations and measurements in laboratory settings, (3) trains advanced students in the use of telescopes and other related instruments within astronomical observatories, and (4) supports research programs that cannot be carried out in larger facilities. These reasons demonstrate the need for small telescopes in the training of prospective members of the astronomical community. Large telescopes are not available for such training purposes because they are inevitably booked months ahead for research astronomers and scientists.

Research.

The SARA (Southeastern Association for Research in Astronomy) facilities promote all areas of observational astronomy. A SARA observatory located on Kitt Peak refurbished a 0.9-meter telescope formerly operated by NOAO. With declining numbers of publicly available small research telescopes, this act greatly helped to improve access to smaller telescopes. The SARA telescope is equipped with a four-port instrument selector that allows use of several instruments during a given night of observation. It is fully computer-controlled with remote robotic scheduling of the telescope through the Internet. The goal of the SARA project is to make the data gathered available to classroom students, as well as to on-site observers.

SARA intends to take an increasing role in helping to represent the interests of astronomers who need smaller telescopes to conduct their research. In fact, SARA has recently become the host institution for the North American Small Telescope Cooperative (NASTeC). The purpose of NASTeC is to emphasis the wide distribution and availability of small-to-medium research telescopes and to coordinate collaboration with astronomy-based projects. The diminishing availability of small telescopes at large, national facilities require that new operating models be developed in order to properly educate the next generation of astronomers. Consortia of small universities such as SARA are one model for meeting these goals.

Future Support

Since many projects involving small telescopes are being terminated in preference to larger telescopes, many members of the astronomical community are actively voicing their support for small telescopes. The advantages of small telescopes began to be told in earnest in October 1996 when astronomers met at the Lowell Observatory, Flagstaff, Arizona. Since then, the American Astronomical Society has featured at least one session devoted to small telescope issues at its meetings.

The momentum, however, clearly belongs to the growing number of large (such as 8-10-meter) telescopes. NOAO director Sidney Wolff concedes that complicated projects involving multi-institutional collaborations continue to demand larger telescopes. However, Wolff also says that small telescopes are making exciting contributions to frontline research, including (1) measuring changes to the expansion rate of the universe, (2) finding optical counterparts to gamma-ray bursts, (3) making precise observations of Sun-like stars in order to understand solar influences on climate change, (4) making direct detection of extrasolar planets, (5) conducting the first deep all-sky survey in the near infra-red, and (6) discovering near-Earth asteroids.

Concerned astronomers have succeeded in saving many of the small telescopes that appeared to be facing retirement during the 1990s. The struggle to keep them open continues as large telescopes dominate the field. Harvard astronomer John Huchra says that, in practice, small telescopes continue to carry much of the workload in astronomy. When used in conjunction with large telescopes and for unique, dedicated purposes ideal for its small size, the small telescope will continue to be a valuable asset to the scientific community. Huchra continues by saying that when small telescopes are used for projects uniquely geared toward their strengths, the small telescope can be incredibly cost effective.

Astronomers have learned that for monitoring broad areas of the sky, imaging the same object night after night, creating worldwide networks of telescopes, automating projects, and other such dedicated uses, small telescopes play an essential role that cannot be filled by their larger counterparts. As long as a mix of both large and small telescope sizes is maintained, then the largest variety of important objectives in astronomical research can continue to be met. However, if the construction of new, large, ground-based telescopes means that smaller telescopes are retired or otherwise abandoned, then our nation's research funds are indeed being poorly allocated.

—WILLIAM ARTHUR ATKINS

Viewpoint: No, the emphasis on the construction of large telescopes is not a poor allocation of resources; on the contrary, such large telescopes are indispensable to the research questions at the heart of modern astronomy.

The invention of the telescope in 1608 is credited to the Dutch spectacle-maker Hans Lipperskey. Italian mathematician, physicist, and astronomer Galileo Galilei (1564-1642) is credited with making the first celestial observations with a telescope in 1609, when he used a "spy-glass" of about 0.05 m (2 in) in diameter.

Classifications

Since Galileo, telescopes that collect electromagnetic waves (such as radio, microwave, infrared, light [visible], ultraviolet, x rays, and gamma radiation) have generally been classified as either: (1) refractors (where radiation is bent, or refracted, as it passes through an objective lens), (2) reflectors (where radiation is reflected by a concave mirror and brought to a focus in front of the mirror), or (3) as a catadioptric system (where radiation is focused by a combination of lenses and mirrors). The telescopes considered in this article are optical; that is, they are used for intercepting visible light (and often also for infrared and ultraviolet "light"). Over the years optical telescopes have gotten bigger and better through the use of increasingly sophisticated structural hardware and software (for example, computer-control of the telescope).

Size Matters

Many of the most recent and important discoveries in astronomy are due to a quest that began soon after the invention of the telescope: to increase the amount of light that is captured and brought to a focus so that astronomers can study increasingly fainter objects. The size of the primary mirror of a telescope determines the amount of radiation that is received from a distant, faint object. The size, quality, and ability to sharply define the details (or the resolution) of an image are all very important characteristics of professional telescopes.

Optical telescopes have circular (or in a few cases, very nearly circular) primary mirrors (the primary mirror is a telescope's main component for intercepting and focusing light). The area of the primary mirror is related to its diameter by the formula A=(π/4)d 2, where "A" is the mirror's area, "d" represents the mirror's diameter, and "π" is a constant (approximately equal to 3.142). This formula demonstrates that a telescope's light-collecting area increases fourfold if its diameter is doubled. For example, using the above equation for the area of a circle, a 4-meter-diameter telescope has an area of about 12.5 square meters, while an 8-meter-diameter telescope (double the diameter of the 4-meter) has an area of approximately 50 square meters. So an 8-m (315-in) telescope has four times the radiation collecting capacity over a 4-m (157-in) telescope. The largest optical telescopes in the world are the twin 10-m (394-in) Keck telescopes on Mauna Kea in Hawaii. In less than 400 years of telescope technology, the Keck telescope has increased the collection of light by 40,000 times over that of Galileo's telescope.

Some of the most important unanswered questions in astronomy have to do with cosmology (the science and origin of the universe). For example, astronomers want to know when, how, and why the galaxies were formed. In order to solve problems like these astronomers need to be able to analyze the radiation coming from the furthest and the faintest objects in the sky. To observe such objects, very large telescopes are indispensable.

Twentieth-Century Telescope Technology

During the twentieth century, advanced telescopes continued to grow in size. Of the two principal types of optical telescopes—refracting and reflecting—the reflecting type long ago won out in the race to build ever-larger telescopes. The largest refractor in existence, with an objective lens of 1.02 m (40 in) in diameter, is located at the Yerkes Observatory in Williams Bay, Wisconsin. A 0.91-m (35-in) refractor is located at the Lick Observatory in California and a 0.84-m (33-in) refractor is located at Meudon, France. These telescopes represent the practical limit to the size of refracting telescopes, whose technological apex was reached near the end of the nineteenth century. In the 300 years of their reign, however, they provided enormously important information about stars, galaxies, and other celestial bodies.

Mount Palomar—1948.

A reflecting telescope of monumental importance in the construction of large telescopes was the 5.1-m (17-ft) Hale Telescope on Mount Palomar, outside San Diego, California. The Hale telescope enabled a string of fundamental discoveries about the cosmos, including critical data on the evolution of stars and the existence of quasars (or "quasistellar radio sources"), thought to be the farthest known objects in the universe yet imaged, billions of light-years away (a light-year is the distance that light travels in vacuum in one year).

Largest Reflectors at Present.

The largest conventional (that is, possessing a single, monolithic primary mirror) reflecting optical telescope is the 8.3-m (27-ft) Subaru telescope at the Mauna Kea Observatory. Other very large reflectors are the 8.1-m (26-ft) Gemini telescope, also at Mauna Kea, the 6-m (20-ft) telescope in the Special Astrophysical Observatory near Zelenchukskaya, in the Caucasus Mountains; and the 5.1-m (17-ft) telescope in the Palomar Observatory in California.

Largest Composition Reflectors. The largest of the reflecting telescopes with segmented or multi-mirror reflectors are the twin W.M. Keck telescopes at the Mauna Kea Observatory in Hawaii. Each has a segmented primary mirror, composed of 36 separate hexagonal pieces. Each segment is about 1.8 m (6 ft) across, creating a 10-m (33-ft) diameter primary mirror. The Keck telescopes began operations in the early 1990s to probe the chemical composition of the early universe, and added to the knowledge that the universe is not only expanding, but also that the expansion is accelerating.

State of the Art

When the 5.1-m (17-ft) Hale Telescope first began to look at the universe in 1948 it was assumed that this size telescope was the largest that could be built without Earth's unsteady atmosphere negating the value of any larger aperture or any better optics. Science correspondent and former program leader of the Artis Planetarium in Amsterdam Govert Schilling wrote that ground-based telescopes languished for several decades at this construction limit. Being outside the Earth's blurry atmosphere, more interest was directed towards space-based telescopes, such as the 2.4-m (8-ft) Hubble Space Telescope (HST) project that started development in the late 1960s.

Beginning in the 1970s Frederic Chaffee, Director of the Multiple Mirror Telescope Observatory, wrote that the computer revolution spawned one of the most intense periods in the design and construction of telescopes. Computers and other new technologies have revitalized the use of large telescopes with current ones being developed in the 6-10 m (20-33 ft) class. The need for the construction of larger ground-based telescopes has to do with the never-ending questions that astronomers pose concerning the deepest mysteries of the cosmos; questions such as "When did galaxies first come into existence?"; "What is the elusive 'dark matter' whose mass is thought to dominate the universe?"; "How many stars have planets?"; and "Do alien worlds possess life?" The list of open questions goes on, tantalizing both astronomers and the general public alike. And many of these questions can only be answered with the use of advanced new large telescopes.

New Large Telescope Technology

Older telescopes, such as the Hale Telescope, contain obsolete technology. These telescopes contain a mirror that has been described as "a huge hockey puck of glass." For instance, the Hale possesses a bulky 26-in-(66-cm)-thick mirror that weighs 20 tons. An enormous support structure is necessary to hold it up, while at the same time forced to adjust to the constant movements necessary to keep up with the Earth's rotation.

By the 1980s new technologies and designs were revitalizing the ground-based telescope field. University of Arizona astronomer Roger Angel cast huge mirrors that were mostly hollow, with a honeycomb-like structure inside to guarantee stiffness. University of California astronomer Jerry Nelson combined 36 smaller sheets that would act as one unit under a computer's control. Another essential technology common to all these new designs is the essential role of sophisticated computers both controlling the telescope and its component parts, as well as aiding in the digital processing of the observed light.

New Large Telescopes and Their Impact

What follows is an overview of just some of the new giant telescopes that are currently in operation—or soon will be—along with some of the uses that each is (or will be) employed to research.

GTC.

The Gran Telescopio Canarias (GTC) at the Roque de los Muchachos Observataory on La Palma in the Canary Islands (Spain) is a high-performance, segmented 10.4-m (34-ft) telescope that will become the largest optical telescope on European territory when it is completed in early 2003. The GTC will consist of a coordinated set of subsystems—including interconnected computers, electronic equipment, cameras, spectroscopes, sensors, and actuators—that will allow the GCS to find extra-solar planets (planets circling stars other than the Sun) and proto-stellar objects (newly forming stars). The GTC will be equipped with an adaptive-optics system that can reduce—and at times eliminate—the Earth's atmospheric blurring.

LBT.

The Large Binocular Telescope (LBT) is being built on Arizona's Mount Graham at a cost of $84 million. When finished in 2004 it will consist of twin 8.4-m (27-ft) telescopes that will ride on a single mounting and be linked by interferometry (to yield the equivalent light-gathering power of a single 11.8-m [39-ft] instrument). Because of its binocular arrangement—a revolutionary optical design—the telescope will have a resolving power (ultimate image sharpness) corresponding to a 22.8-m (75-ft) telescope. The LBT will thus have a collecting area larger than any existing or planned single telescope. It will provide unmatched sensitivity for the study of faint objects.

SALT.

The Southern African Large Telescope (SALT) will be completed around December 2004 as the Southern Hemisphere sister to the Hobby-Eberly Telescope at the McDonald Observatory in Texas. Its innovative design consists of an 11-m (36-ft) wide segmented (hexagonal) mirror array that will have a clear aperture of 9.1 m (30 ft). At a cost of $30 million it will be a specialized instrument designed only for spectroscopy (the investigation and measurement of the radiation spectrum). SALT will be able to record distant stars, galaxies, and quasars a billion times too faint to be seen with the unaided eye.

Mauna Kea.

As discussed previously, on Mauna Kea in Hawaii the Subaru Telescope contains a mirror more than 8.3 m (27 ft) across; the Gemini North Telescope is 8.1 m (26 ft) across; and the twin Keck telescopes possess light-gathering surfaces 10 m (33 ft) in diameter. Geoff Marcy, from the University of California, has so far discovered 35 planets orbiting Sun-like stars, in part, using the Keck telescope. Marcy says that lesser telescopes would be unable to detect the gravitational wobble that he looks for when scouring the sky for planets. So far he has found a planet the size of Saturn, and with the use of even larger telescopes hopes to soon discover smaller planets the size of Neptune.

The Keck telescopes, as segmented mirror structures where adjacent segments stay aligned to millionth-of-an-inch optical tolerances, have made an enormous number of discoveries. California Institute of Technology professor George Djorgovski has concentrated on gamma-ray bursts—mysterious flashes of high-energy radiation—that appear to be billions of light-years away. Djorgovski says that the Keck telescopes have allowed him to solve the mystery of these bursts. University of California astronomer Andrea Ghez has used the Kecks for her exploration of the Milky Way's core. An electronic camera sensitive to infrared radiation that is attached to the telescopes has allowed Ghez to penetrate the dust that surrounds the center. Through this combination of instruments Ghez has been able to measure the motion of stars that lie 100 times as close to the galactic core as the nearest star (Proxima Centauri) is to the Sun. Ghez has declared that these stars are traveling 100 times as fast as Earth orbits the Sun (at nearly 1,600 mi [2,574 km] per second).

Adaptive Optics and Interferometry

The technology called adaptive optics (AO) is a process that "de-twinkles" starlight. Stars and galaxies twinkle because the Earth's turbulent atmosphere acts to deform incoming starlight. AO, through the use of computers, measures the amount of twinkle and cancels it out by deforming the surface of a flexible mirror. Astronomers have used this advanced technology at both the Keck and Gemini telescopes to take pictures as clear as the Hubble Space Telescope. Senior Editor for Sky & Telescope Roger W. Sinnott asserts that the Arizona's Large Binocular Telescope should reveal the universe ten times more sharply than the space-based Hubble due to the use of AO!

The resolution of telescopes can be improved with a process called interferometry. Light is combined from widely separated telescopes to result in precision never before seen in telescopes. By sampling incoming light at two or more different vantage points, it is possible to simulate the resolution of a single gigantic telescope, whose diameter equals the distance between the outer edges of the farthest-spaced mirrors. This is the technology that will be employed with the Large Binocular Telescope.

Super-giant Telescopes

New technology is allowing bigger, lighter mirrors to be made more quickly than ever before. In addition, the limitations on the sharpness of telescope images are also being overcome. Technologies to cut through the distortion of the Earth's atmosphere is promising to allow the study of the universe to ever fainter, more distant limits and with unprecedented clarity. John Huchra, professor at the Harvard-Smithsonian Center for Astrophysics, has said, "What's been happening in the telescope game is incredible." For the foreseeable future, these advances in viewing new celestial phenomena can only be accomplished with the new class of large telescopes.

But telescope designers are not stopping at 6-10-m (20-33-ft) telescopes. Designs are being contemplated for the next generation of ground-based telescopes, now being called super-giant telescopes, with a projected range of size from 30 m (100 ft) to a staggering 100 m (330 ft). These football-field-sized telescopes—in reality hundreds of individual mirrors aligned to make a single giant telescope—could have 100 times the light-gathering capability of the Keck telescopes.

All these new and envisioned technologies for large and ultra-large telescopes are revolutionizing astronomy. Large telescopes are taking advantage of the latest sensors, fastest computers, adaptive optics, and other technologies in order to achieve resolutions and image sharpness at levels far exceeding that of even the Hubble space telescope. Though smaller telescopes definitely have their place in astronomy, the really big, new findings in astronomy are being achieved with the latest generation of large, ground-based telescopes. Allocating the lion's share of resources in astronomy to the operation and construction of this new class of large telescopes—even at the reduction or retirement of their smaller cousins—is not only advisable, it is indeed essential to the progress of the science of astronomy, and to the continuing effort to understand our place in the universe.

—PHILIP KOTH

Further Reading

Benn. C. R., and S.F. Sánchez. "Scientific Impact of Large Telescopes." The AstronomicalSociety of the Pacific 113, no. 781 (March 2001): 385-96.

"Big Scopes Aren't Always Best." Sky and Telescope 101, no. 2 (February 2001): 24.

Chaffee, Frederic. "Telescopes for the Millennium." Technology Review 97, no. 2 (February/March 1994): 52.

De Grasse Tyson, Neil. "Size Does Matter." Natural History 108, no. 7 (September 1, 1999): 80.

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KEY TERMS

ELECTROMAGNETIC:

A disturbance that propagates outward from any electric charge that oscillates or is accelerated; far from the electrical charge, it consists of vibrating electric and magnetic fields that move at the speed of light and are at right angles to each other and to the direction of motion.

GAMMA RAY BURSTS:

Intense blasts of soft gamma rays originating at extreme distances from Earth, which range in duration from a tenth of a second to tens of seconds, and which occur several times a year from sources widely distributed over the sky.

GROUND-BASED:

Pertaining to instruments or devices

(such as telescopes) that are fixed to Earth's surface.

INTERFEROMETRY:

The design and use of optical interferometers (instruments in which light from a source is split into two or more beams, and subsequently reunited after traveling over different paths, in order to display interference).

OPTICAL:

Relating to objects (such as stars) that emit waves in the visible portion of the electromagnetic spectrum; also, instruments (such as telescopes) that gather and manipulate light.

QUASARS:

Massive and extremely remote celestial objects that emit exceptionally large amounts of energy; they typically have a star-like appearance in a telescope.

RADIATION:

The emission and propagation of waves transmitting energy through space or through some medium.

SPECTROSCOPY:

The branch of science concerned with the investigation and measurement of spectra produced when matter interacts with or emits electromagnetic radiation.

SUPERNOVAE:

Stars that suddenly increase greatly in brightness because of catastrophic explosions that eject the vast majority of their masses.

TELESCOPE:

An instrument for viewing celestial objects by the refraction (bending) of light via lenses, or by the reflection of light via mirrors.

PROFOUND QUESTIONS ASKED BY ASTRONOMERS

There are many profound questions that astronomers hope to someday answer with the use of some of the world's most powerful telescopes. Scientists at the National Research Council recently stated that resolution of such questions could allow science to take giant leaps forward in knowledge about the physics of the universe.

Astronomers currently can account for only about 4% of ordinary matter in the universe. What is dark matter? is a question that, once answered, will tell what types of "dark matter" make up the missing universe. The leading dark matter candidates are neutrinos and two fairly unknown particles called neutralinos and axions. These particles are predicted by some physics theories but have never been detected.

What is dark energy? is an associated question to dark matter that also must be answered to explain the structure of the universe. After adding up all the potential sources for ordinary matter and dark matter, the total mass density of the universe comes up about two-thirds short. The missing energy could mean that the vacuum of space is not a true emptiness (or void). Instead, space might be filled with vacuum energy, which is a low-grade energy field created when ordinary particles and their antimatter sidekicks periodically burst into and out of existence.

When Albert Einstein asked the question What is gravity? he extended Isaac Newton's concept of gravity by taking into account extremely large gravitational fields and objects moving at velocities close to the speed of light. However, Einstein did not consider quantum mechanics, an area of extremely small gravitational fields that has never been experimentally observed. For instance, near the center of black holes gravitational forces are very powerful at extremely small distances. These energies violate the laws of quantum mechanics and cannot totally explain the concept of gravity.

The four dimensions of space and time are easily observed. The current string-theory model of the universe combines gravity with 11 dimensions. Astronomers cannot see these 11 dimensions because their instruments are too crude to answer the question: Are there additional dimensions?

Additional questions such as How did the universe begin? will be answered, along with many more, only through the use of larger and larger telescopes. These super-telescopes will help astronomers and scientists explain the physics of the universe.

William ArthurAtkins

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Is the emphasis on the construction of very large ground-based telescopes (6-10 meters) at the expense of smaller telescopes (1-4 meters) a poor allocation of resources

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Is the emphasis on the construction of very large ground-based telescopes (6-10 meters) at the expense of smaller telescopes (1-4 meters) a poor allocation of resources