BOX 1.1 Some Highlights of Discoveries of the 1990s in Astronomy and Astrophysics

  • Discovery of planets orbiting other stars

  • Determination of the interior structure of the sun from observations of its seismic activity

  • Discovery of Kuiper Belt objects, a large group of small, primitive bodies in the outer solar system

  • Observation of the impact of Comet Shoemaker-Levy 9 on Jupiter

  • Discovery of “brown dwarfs,” cool stars too small to sustain nuclear reactions in their centers

  • Discovery of gravitational microlensing of the light of background stars by intervening objects of stellar mass

  • Discovery that gamma-ray bursts originate in the very distant universe

  • Discovery of massive black holes in the nuclei of galaxies, including our own Milky Way

  • Discovery of young galaxies at redshifts greater than 3, revealing the dramatic evolution of galaxies from the early universe to the present

  • Discovery of theoretically predicted tiny fluctuations in the background radiation left over from the big bang, the seeds of subsequent structure formation

  • Measurement of the expansion rate of the universe to an accuracy near 10 percent and determination that there is not enough matter to stop the expansion of the universe

  • Evidence suggesting both that the universe is “flat” and that its expansion is accelerating owing to the presence of “dark energy”

SOURCE: Adapted from National Research Council, Astronomy and Astrophysics in the New Millennium, National Academy Press, Washington, D.C., 2001, pp. 18–19. For nearly every discovery, both NSF and NASA supported the U.S. researchers who used both ground- and space-based facilities, and for some the Department of Energy provided key support as well.

nos. One remarkable aspect of the major discoveries listed in Box 1.1 is the fact that both ground- and space-based observations played important roles in practically every breakthrough, and this trend is expected to increase. The process of identifying the likely sources of cosmic gamma-ray bursts (Box 1.2) provides a good example of the synergy and interdependence between space and ground observing techniques.

Similarly, contemporary astronomy and astrophysics cannot be parsed by wavelength, by the location of the observing instruments, or by nationality. For example, Box 1.3 describes some of the science that will be enabled by the complementary nature of three future international facilities—the Next Generation Space Telescope, the Giant Segmented Mirror Telescope, and the Atacama Large Millimeter Array—that will observe the universe at different wavelengths and from the ground and in

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