Planetary Sciences Division 

 Brian Marsden, Associate Director 



Research in Planetary Sciences is carried out along observa- 

 tional, laboratory, computation, and theoretical lines by scien- 

 tists with training either in geology or in 

 astronomy/astrophysics. Traditionally, this division has been 

 concerned with the small bodies of the solar system, including 

 meteors, with particular interest in the positional observation 

 and orbital determination of comets and minor planets. This 

 division also serves as headquarters for the International Astro- 

 nomical Union's Minor Planet Center and Central Bureau for 

 Astronomical Telegrams. Among specific projects is a 

 study of the long-term effects of Jupiter and Saturn on the 

 population of the outer part of the asteroid belt. Another 

 effort seeks to increase significantly the rate of discovery 

 and appropriate followup of near-Earth asteroids (or com- 

 ets). Geological research mainly involves the petrology of 

 extraterrestrial materials, in particular meteorites and lunar 

 samples. Other research involves the early conditions in the 

 primitive solar nebula. 



Radio and Geoastronomy 

 Mark Reid, Associate Director 



Research in the Radio and Geoastronomy Division covers a 

 wide range of topics in radio astronomy, including the study 

 of the formation of stars, evolved stars, supernovae, the struc- 

 ture of the Milky Way, and extragalactic radio sources. Obser- 

 vations ot continuum and spectral line sources are conducted 

 with a wide variety of instruments ranging from single anten- 

 nas to interferometers such as the Very Large Array (VLA). 

 The Division is currently in the process of building a major as- 

 tronomical facility: a 6-elernent submillimeter wavelength 

 telescope array (SMA) to be located near the summit of Mauna 

 Kea, Hawaii. The SMA is intended to make observations with 

 unprecedented tesolunon in the still largely unexplored sub- 

 millimetet band between radio and infrared wavelengths. 

 Other research in the division includes the application of 

 radio astronomy techniques to the study of geophysical prob- 

 lems, tests of general relativity, and the development ot 

 atomic clocks. Also, designs for satellite-borne optical inter- 

 ferometers and space-based applications of tethered satellites 

 are being developed. 



Solar and Stellar Physics 



John Raymond, Associate Director 



Scientists in the Solat and Stellar Physics Division carry out a 

 wide range of research projects using data from x-ray and 

 ultraviolet satellite observatories and telescopes on the 

 ground. Major themes include the study of stellar coronae 

 based on ultraviolet emission, investigation of the formation 

 and early development of stars, and analysis of the surface lay- 

 ers of the Sun. 



The atmosphere of the Sun, our nearest star, contains complex 

 magnetic structures which influence both solar radiation and the 

 solar wind — the stream of energetic particles ejected at high 

 speeds that bathe the bodies of the solar system, including Earth, 

 with profound impacts on life. By designing and building in- 

 creasingly sophisticated experiments to study the Sun's hot outer 

 atmosphere, SAO scientists were the among first to identity the 

 dominance of magnetic fields. In addition, the SAO-inspired 

 interdisciplinary study of the Sun and stars has applied detailed 

 knowledge of the solar corona to understand those processes 

 which govern the coronae of distant stars. SAO also continues to 

 study cycles and activity in stars like the Sun, with the goal of 

 identifying and predicting the behavior of our own star. 



Theoretical Astrophysics 



A.G.W. Cameron, Associate Director 



An underlying goal of astrophysical research is to understand 

 as much of the universe as possible within the current state of 

 technological development. Data come from astronomical ob- 

 servations carried out with equipment collectively sensitive to 

 the entite range ot the electromagnetic spectrum — from long- 

 wavelength radio waves to very short-wavelength gamma 

 rays. In the last three decades, access to space and the techno- 

 logical development of sensitive new detectors and fast com- 

 puters has revolutionized the gathering of data about the 

 universe. Transforming that data into information and under- 

 standing is the role of theory. The increasing use ot super- 

 computers to construct analytical models of objects, or 

 simulations, has transformed the theoretical approach to such 

 an extent that computational astrophysics is now considered 

 on par with observational and theoretical astrophysics. Com- 

 putational astrophysics requires that the simulation programs 

 incorporate enough detailed physics for the results to bear a 

 close resemblance to reality. This division attempts to apply 

 such an analytical and computational approach to understand- 

 ing the universe. 



SAO Highlights of 1995 

 Research 



An experiment to probe the fundamental laws of physics by 

 searching for evidence of a permanent electric dipole moment 

 in an atom led to development of an innovative technique for 

 the laser magnetization of xenon gas. In a cooperative pro- 

 gram with doctors at Harvard Medical School, the laser-gener- 

 ated xenon is being applied to the enhancement of magnetic 

 resonance imaging (MRI) to allow imaging of parts of the 

 body, such as the brain, which cannot be imaged well with 

 current techniques. 



Smithsonian Astrophysical Observatory scientists and their 

 colleagues found by far the bset evidence for the existence of 

 massive black holes. The discover)' was based on radio observa- 

 tions of swirling gas orbiting a very dense concentration of 

 material with the mass of about 40 million Suns. 



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