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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS 8 Astronomy as a National Asset Astronomy makes humanistic, educational, and technical contributions to our society. The most basic contribution of astronomy is that this science provides modern answers to questions about humanity 's place in the universe. We can now give quantitative answers to questions about which ancient philosophers could only speculate. In addition to satisfying our curiosity about the universe, astronomy nourishes a scientific outlook in society at large. Society invests in astronomical research and receives an important dividend in the form of education, both formally through instruction in schools, colleges, and universities, and more informally through television programs, popular books and magazines, and planetarium shows. Astronomy introduces young people to quantitative reasoning and helps attract them to scientific or technical careers. Modern astrophysics also contributes to areas of more immediate practicality, including industry, medicine, and defense. OUR PLACE IN THE UNIVERSE As far back as history records, we humans have attempted to understand the origins of the universe and our place in it. The Copernican revolution showed that the earth was not the center of the universe, but rather only one of several planets orbiting the sun. With further study, our sun was recognized as a typical star, located far from the center of a normal galaxy. Astrophysical measurements of the motions of binary stars and of the atomic transitions of various elements in nearby stars and distant galaxies have demonstrated that the laws of physics are the same at distant times and places as here and now on
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS the earth. Modern cosmological models suggest that the universe is only three or four times older than the earth itself and that the universe has neither center nor edge. Astronomy helps reveal the nature of life and its fragility. Our knowledge of the formation of the elements tells us that we are “stardust,” formed from material built up in the early seconds of the universe or in the interiors of massive stars. Chemical reactions of carbon atoms with other atoms in interstellar gas and in meteorites produce the same molecules that are the building blocks of living creatures on the earth. Looking down at the earth from orbit, we see our home as a small, fragile entity. Observing the inhospitable environments of Mars and Venus lends reality to concerns for the future of our own ecosystem. As new instruments expand our capability to peer deeper into space, our view of the universe expands and evolves. Astronomers know that although any given interpretation may be outmoded by a new observation, the basic process of empirical inquiry is sound and leads to a better understanding of the world around us. Astronomers can offer to their fellow citizens the confidence that the universe is comprehensible. ASTRONOMY AND AMERICA'S SCIENTIFIC LEADERSHIP Public Scientific Literacy Reports such as A Nation at Risk (NCEE, 1983), A Challenge of Numbers: People in the Mathematical Sciences (NRC, 1990a), and Physics Through the 1990s (NRC, 1986a) have called for improvements in public education at all levels, and particularly in science. Astronomy and astrophysics have an important role to play in maintaining and restoring American leadership in science and technology by raising the level of scientific literacy among the general public and students at all levels, by inspiring students to become scientists, and by training scientists for other technical careers. Astronomical concepts are usually included as part of the physical sciences courses taken by elementary and junior high school students and occasionally appear as parts of high school curricula. Project STAR (Science Through its Astronomical Roots) is being developed at the Center for Astrophysics to provide astronomical course material for high school chemistry and physics classes. Project 2061, which aims to ensure scientific literacy among all high school graduates by the year 2061, when Halley's Comet returns, has a significant astronomical component. Astronomy is also the focus of many successful adult education courses and teacher training programs. Formal astronomy courses probably have their greatest impact at the non-major undergraduate level. Colleges and universities with astronomy (or physics and astronomy) departments had 1.2 million undergraduates in 1988;
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS about 8 percent of these students took introductory astronomy (Sadler et al., 1989). Large numbers of students also learn about science from astronomy courses given in institutions without formal astronomy departments. Cosmos, the most successful experiment ever in public scientific education, has had an audience of 400 million television viewers in about 60 countries. The book Cosmos (Sagan, 1983) is the best selling English-language science book in history. But Cosmos is only one of the ways that astronomy is presented to the public. Project Universe, a series of 30 half-hour programs, had its hundredth showing last year. NOVA often features astronomical subjects. The daily radio feature “Stardate,” produced at the University of Texas, is broadcast by about 200 stations and has attracted half a million letters from listeners in the past decade. While astronomers make up only 0.5 percent of the scientists in the United States, science magazines such as Scientific American, Discover, and Science Digest devote about 7 percent of their pages to astronomy. Over the last 10 years, astronomy articles outnumbered those on biology and nearly equaled the number of articles on physics in some of the most prestigious newspapers. Of the 10 best-selling nonfiction books on the New York Times list in 1988, three were on astronomy. The intellectually demanding A Brief History of Time (Hawking, 1988) spent over two years on the New York Times best seller book list. About 250,000 enthusiasts subscribe to Sky and Telescope or Astronomy magazine. Planetariums and observatories reach millions of children and adults. Mc-Donald, Palomar, and Kitt Peak Observatories each record almost 100,000 visitors per year. The Griffith Observatory and its associated planetarium in the hills above Los Angeles hosted 1.7 million people in 1988, as many as the Los Angeles County Museum of Art and the J.P. Getty Museum together. Training of Professional Scientists A steadily decreasing number of people in the United States are pursuing careers in science and engineering. Our economy depends on our ability to compete technologically with other nations. The quality of the environment depends on developing safe, clean industries and sources of energy. None of this can be accomplished without a work force of imaginative and highly trained scientists and engineers. In what ways can astronomy contribute? First, because of its broad appeal, astronomy is often the science that initially arouses the scientific interests of people who eventually earn degrees in other technical disciplines. For example, two long-standing summer programs in astronomy for outstanding high school students, at the University of Illinois and at the Thacher School in Ojai, California, have inspired nearly all their participants to go on to college programs in science, engineering, mathematics,
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS or medicine. Chapter 7 makes specific recommendations about enhancing the role of astronomy in science education at the precollege and college level. About 70 American colleges and universities currently offer degrees in astronomy, astrophysics, or closely related fields. Recipients of bachelor's degrees in astronomy are widely diffused in technical fields. Surveys of students (Ellis and Mulvey, 1989) suggest that about half go on to graduate school in physics, engineering, geology, and atmospheric science as well as astronomy (Figure 8.1); the other half are employed mostly in technical industrial firms. Most recipients of graduate degrees in astronomy establish lifetime careers in astronomical research and teaching. However, surveys conducted at the California Institute of Technology and the University of Maryland suggest that about 40 percent of those who earn doctorates in astronomy eventually move into research and teaching in other fields, or take jobs in government, industry, or defense. A graduate degree in astrophysics provides a good match to the requirements of scientific defense work. About 100 members of the American Astronomical Society are currently employed at Los Alamos and Lawrence Livermore National Laboratories; an even larger number are engaged in full-or part-time defense work elsewhere. SYNERGISM WITH OTHER SCIENCES The universe is a laboratory far grander than any constructed on the earth. The extreme conditions reached in astronomical systems, of high and low temperatures, of high and low densities, of common and rare elements, provide unique tests of physical theories. High-Energy and Particle Physics Astronomical observations are helping to clarify the properties of the neutrino, an elusive elementary particle whose nature is poorly understood. For example, the best limit on the charge of the neutrino is based on observations of the neutrino burst associated with Supernova 1987A. One of the most intriguing problems in high-energy physics originated in an attempt to use neutrinos to look into the nuclear-burning core of the sun and thereby test directly the theories of stellar evolution and nuclear energy generation in stars. As a result of the discrepancy that arose when observations disagreed with predictions, many new testable ideas regarding neutrinos were developed. While some of these theories proposed changes to models of the solar interior, others have raised questions about the fundamental physics of the neutrino. The explanation of the conflict between observation and theory for solar neutrinos may ultimately provide evidence for lepton nonconservation and for at least one neutrino having a non-zero mass.
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS FIGURE 8.1 The training of astrophysicists can include building advanced equipment. Here Berkeley graduate student Ning Wang assembles a prototype of a cryogenic detector being built for the search for weakly interacting dark matter particles. Photograph courtesy of Technical Information Department, Lawrence Berkeley Laboratory, University of California.
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS Geophysics Techniques from radio astronomy are being used to measure the motion of the earth's continents. Very long baseline interferometry (VLBI), normally used to measure the positions of celestial radio sources, also measures the position of radio telescopes to a few centimeters. VLBI has determined that the rate of slippage along the San Andreas fault, and the rate at which the Atlantic Ocean is widening, is from 1 to 3 cm per year. Astronomers also study the geology of other planets, thereby giving geologists a better perspective on terrestrial problems. Examples include insights into vulcanism and tectonic mechanisms obtained by comparing Earth to Mars, Venus, Io, and Triton. ASTRONOMY AND THE EARTH'S ENVIRONMENT An Astronomical Context for the Earth's Environment The energy from the sun is a critical parameter determining the habitability of the earth. There are tantalizing hints of terrestrial climatic changes on long time scales driven by changes in the solar luminosity and in the earth's orbit around the sun. We need to understand solar effects on our environment in order to isolate and better understand human perturbations on the environment. Measurements from space during the most recent solar cycle show that the total brightness of the sun changes about 0.1 percent between maximum and minimum activity (Figure 8.2). Most models suggest that such changes should cause a minor global temperature change of less than 0.1°C. However, the integrated solar activity, smoothed over several cycles, has increased roughly in phase with the apparent 0.5°C warming trend of the past century; the Little Ice Age in the 1600s coincided with an extended period of exceptionally low solar sunspot activity. We need to understand more about climatic cycles on both the sun and the earth to determine how significant these effects are. A promising way of understanding solar cycles is to compare the sun with the other stars known to have 5- to 20-year cycles. There are numerous short-term effects of sudden increases in the ultraviolet, x-ray, and particle radiation coming from the sun. The high-energy radiation from such flares hits the earth's upper atmosphere, causing heating and ionization, and also modifies terrestrial electric and magnetic field structures on the ground. The 11-year cycle of solar activity reached near-record levels in 1989. Documented effects of large solar flares include major power outages, disruption of radio communication, and added drag on satellites. Continuous monitoring of the sun can give a few hours warning of the arrival of particles from solar flares. These observations will be important for the safety of astronauts inhabiting, or traveling to, the moon or Mars.
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS Models of the Earth's Environment Questions of long-term climate change and the influence of humans on the earth's environment are of concern to citizens and governments. Much of the research on which the discussion is based originated in attempts to explain the climates of other planets, including Venus with its runaway greenhouse effect, Mars with its thin atmosphere, and Jupiter, Saturn, and Neptune with their dramatic storm systems (Plate 8.1). Astronomers and atmospheric scientists have developed models to help understand and eventually predict the dynamics of planetary atmospheres and the physical conditions that result in environments hospitable to life. Some of the models work tolerably well for the simplest planetary atmosphere, that of the planet Mars, but fail for more complex planets, including our own. These models can be improved by comparison with the observations of other planets to make reliable predictions for our own environment. Astronomy, Weather, and Ozone Depletion Weather satellites are one of the practical benefits of the space age. The tropospheric temperature sounders used in national security applications and soon to be used in civilian weather satellites are direct descendants of the planetary radio astronomy instruments used to probe the atmosphere of Venus. Remote sensing from satellites is one of the best methods for monitoring the earth's ecosystem. Radio astronomers, for example, have adapted the techniques of millimeter wave astronomy to studies of ozone depletion. In 1977 astronomers initiated a program to measure the stratospheric concentration of chlorine oxide (ClO), the most important tracer of the destruction of ozone by chlorofluorocarbons. Measurements of the diurnal variation of ClO in the middle stratosphere provided a critical test of the proposed photochemical models (Solomon et al., 1984). Subsequent measurements of the high concentration of ClO in the lower stratosphere during early spring and its subsequent disappearance in October (de Zafra et al., 1987), when ozone levels returned to normal, demonstrated that chlorine chemistry was responsible for the Antarctic ozone hole (Plate 8.2). Automatic millimeter wave instruments built by a commercial company founded by astronomers will measure both ozone and ClO as part of a worldwide network. Atmospheric ozone also varies significantly due to natural causes. The solar activity cycle produces an 11-year variation in the sun 's ultraviolet radiation, and this in turn affects the terrestrial ozone abundance. Solar variability in the ultraviolet must be known in sufficient detail to delimit the natural causes of ozone change before one can confidently extract the man-made component of that change. Ultraviolet solar variability is thus of practical as well as astronomical interest.
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS FIGURE 8.2 Instruments on the Solar Maximum Mission and Nimbus-7 satellites measured a small-amplitude (0.1 percent) variation in the total energy output of the sun during the past 11-year activity cycle (a, facing page). These variations are associated with measured changes of heating in the sun's atmosphere (b, facing page), which also can be seen in other stars like the sun (c, above). The study of stars like the sun gives us more data on these variations in luminosity and provides a context in which to understand long-term variations in the terrestrial climate. Figure (a) reprinted by permission from Hickey et al. (1988), copyright © 1988 by Pergamon Press; figure (b) courtesy of W. Livingston and O.R. White, National Solar Observatory; and figure (c) courtesy of S. Baliunas, Mt. Wilson Observatory. USES OF ASTRONOMICAL TECHNIQUES OUTSIDE ASTRONOMY Useful applications often arise when scientists develop new research techniques. A few examples of the application of astronomical techniques outside astronomy are described below; more are cited in Table 8.1, Table 8.2, Table 8.3 and Table 8.4. Astronomers are currently working on infrared imaging devices suitable for low light levels, special-purpose computers for following simultaneously the motions of thousands of particles, and low-noise radio receivers for submillimeter wavelengths. No one can state for certain what these new devices will be good for, but as Michael Faraday replied, when questioned by the then British Chancellor of the Exchequer William Gladstone about the utility of his new theories of electricity, “Why, Sir, there is every probability that you will soon be able to tax it.” Medicine Medicine and astronomy share the problem of imaging the inaccessible. Astronomers, especially radio astronomers, led the way in solving the general problem of reconstructing the two- or three-dimensional appearance of objects from a number of one- or two-dimensional scans (Table 8.1). A paper by Bracewell and Riddle (1967) is widely cited in the nonastronomical literature. Some of the image-reconstruction techniques of radio astronomy are now used
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS TABLE 8.1 Medical Applications of Astronomical Techniques Astronomical Technique or Device Medical Uses Image reconstruction from one- and two-dimensional scans of radio sources Imaging for CAT scans Magnetic resonance imaging Positron emission tomography Microwave receivers Scans for breast cancer Image-processing software (IRAF and AIPS) developed by NRAO, NOAO, and NASA Cardiac angiography Monitoring neutron activity in brain Positive pressure clean rooms for assembly of space instruments Cleaner hospital operating rooms Detection of faint x-ray sources Portable x-ray scanners (Lixiscope) for neonatology and Third World clinics in medical imaging that includes CAT scans, magnetic resonance imaging, and positron emission tomography. Microwave receivers developed by radio astronomers are used in scans for breast cancer. Industry Radio astronomy has been a particularly fruitful source of useful technology and algorithms. The Millitech Corporation, whose founders are radio astronomers, builds millimeter wavelength components, largely for the communications industry. The National Radio Astronomy Observatory (NRAO) has improved low-noise receivers, some of which have given rise to commercial products (Table 8.2). Computer programs used to control telescopes and to make maps from interferometers have found wide application in industry. The effort to produce ever better emulsions for astronomical purposes led the Kodak Company to the discovery of gold sensitization, which made possible not only Tri-X film but an entire generation of 400-ASA films. Technical Pan, the film of choice for most industrial and fine arts photographers because of its fine grain and high resolution, first served to record changes on the surface of the sun. The infrared emulsions that astronomers first requested have proved useful in aerial reconnaissance and more recently in remote sensing of the earth's resources. Defense Technology The technical needs of some astronomical facilities and of certain national security programs are so similar that advances in one field often find applications
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS TABLE 8.2 Industrial Applications of Astronomical Techniques Astronomical Technique or Device Industrial Uses Image-processing software (AIPS, IRAF) General Motors Co. study of automobile crashes; Boeing Co. tests of aircraft hardware Holographic methods for testing figures of radio telescopes Testing communications antennas Development of low-noise receivers by NRAO, universities Components for communications industry FORTH computer language developed by NRAO for control of radio telescopes 20 vendors supply FORTH for applications including analysis of auto engines in 20,000 garages, quality control for films at Kodak, 50,000 hand-held computers used by express mail firm Gold sensitization of photographic plates Development of Tri-X and 400-ASA films by Kodak Infrared-sensitive films for spectroscopy Aerial reconnaissance and earth resources mapping X-ray detectors for NASA telescopes Gas chromatographs to search for life on Mars Baggage scanners at airports in the other. Progress in military technology, from World War II radar to present-day infrared detectors, has greatly enhanced astronomical capabilities. Yet astronomical data and techniques developed for astronomy have also proven useful for national security goals. Satellite and aerial surveillance requires lightweight telescopes, precise optical instruments, and the ability to process numerous imperfect images to extract the maximum available information. Development of the necessary mirror technology, the ability to adapt optics to rapidly changing conditions, and the processing algorithms have, from the U2 airplanes of the 1960s to the KH-11 satellites of the 1980s, involved people originally trained as astronomers. Astronomers have also made important scientific and technical contributions to defense-related interests in the infrared wavelength range. For example, astronomers preparing instruments for the Hubble Space Telescope worked with researchers at the Honeywell Corporation and the Rockwell International Company to improve greatly the sensitivity of 1- to 2.5-µm infrared arrays. The Air Force Geophysics Laboratory rocket program produced pioneering data on the infrared sky, but NASA's Infrared Astronomical Satellite (IRAS) definitively
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS TABLE 8.3 Defense Applications of Astronomical Techniques Astronomical Technique or Device Defense Uses Stellar observations and model atmospheres Discrimination of celestial objects from rocket plumes, satellites, and warheads Infrared all-sky survey by NASA's IRAS satellite Detectors for gamma-ray and x-ray astronomy Vela satellite monitors for nuclear explosions Detection of nuclear reactors on Soviet spacecraft Positions of quasars and stars Precision navigation for civil and military purposes measured the celestial infrared background against which orbiting satellites and incoming warheads must be detected (Table 8.3). Astronomers working on x- and gamma-ray detectors at Los Alamos also helped build the instruments for the Vela satellites that monitored the earth for atomic explosions during the 1960s and 1970s. Two gamma-ray instruments operated for astronomical research independently confirmed the presence of nuclear reactors on several Soviet satellites. Why They Call It Universal Time Astronomical, civil, and defense interests overlap in their need for precise coordinate systems and timekeeping. Nonastrophysical uses include navigation, clock synchronization, ballistic missile guidance, and secure communications. The most accurate time standard for periods in excess of a few months may be extraterrestrial, with the recently discovered pulsars with millisecond periods proving to be the most accurate clocks in the galaxy. The fundamental celestial coordinate system used for navigation is now based on radio astronomy. The locations of the satellites that make up the Global Positioning System are soon to be tied to the fixed positions on the sky of distant quasars. Inertial guidance systems (for missiles and other purposes) require this accurate astronomical coordinate system for their calibration. Finally, because satellite orbits are independent of the assorted wobbles of the earth beneath, the accurate location of terrestrial features requires accurate forecasts of the earth's orientation. The U.S. Naval Observatory disseminates this information based on optical and radio observations of quasars.
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS TABLE 8.4 Environmental Applications of Astronomical Techniques Astronomical Technique or Device Environmental Uses Millimeter wave spectroscopy Study of ozone depletion Models of planetary atmospheres Global change modeling Measurement of variations of sun and solar-type stars Study of global climatic change Study of sunspots and solar flares in sun and stars Short- and long-term prediction of terrestrial effects Models of astrophysical shocks Study of terrestrial storms Precision measurement of quasars Geodesy and study of tectonic drift Composite materials for orbiting infrared telescope Design of solar collectors Theory of cosmic rays, solar flares, and stellar fusion Design of fusion reactors Energy Key ideas in the controlled magnetic thermonuclear fusion program in the United States were provided by an astronomer who adapted ideas first considered in connection with cosmic rays and with nuclear fusion in stellar interiors (Table 8.4). The diagnostic tools developed for the study of solar flares and other hot, magnetized plasmas have proven useful in the investigation of the magnetic confinement of fusion plasmas on the earth. The search for alternative energy sources has also benefited from astronomical spin-offs. A private company has built solar radiation collectors up to 16 m in diameter using graphite composite materials first developed for a proposed orbiting telescope, the Large Deployable Reflector. The material is both light and resistant to temperature-induced distortions. ASTRONOMY AS AN INTERNATIONAL ENTERPRISE Astronomers have a long history of international collaboration, dating back to a network of comet observers established by Newton and Halley in the 17th century. The International Astronomical Union was the first of the modern international scientific unions organized under the Versailles treaty. The need for observatories all around the earth to cover the whole sky at all times encourages international collaborations. The names of the European Southern Observatory, the International Ultraviolet Explorer, and the Canada-FranceHawaii Telescope are self-explanatory. The latter shares the top of Mauna
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS Kea in Hawaii with a British infrared telescope and several American projects. Construction of a Japanese observatory on Mauna Kea is expected to begin in the next decade. Other success stories include NASA's IRAS satellite, a joint U.S., U.K., and Netherlands enterprise; an American spectrometer launched by a Japanese rocket to study cosmic radio waves; an American instrument on the Soviet Vega spacecraft that flew past Comet Halley; and a worldwide network of telescopes to study seismic oscillations of the sun. Scientists in the United States and the USSR will work together on a Soviet orbiting telescope for very long baseline interferometry called RadioAstron. This program builds on a history of collaboration between Soviet and American radio astronomers that survived the most difficult periods of the Cold War. Civilization reaps the benefits of astronomy as an international enterprise. The first images from space showing the earth as a planet displayed the fragility of our planet and emphasized the need for worldwide cooperation in studying the earth and the universe it inhabits.
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