|Annu. Rev. Astron. Astrophys. 1999. 37: 445-486
Copyright © 1999 by Annual Reviews. All rights reserved
2.1. The First Palomar Discoveries
Among the first of the interesting discoveries that often made the newspapers, even in the 1950s, occurred at Palomar during the initial trials with the 48-inch Schmidt prior to the beginning of the National Geographic-Palomar Sky Survey mapping. Baade, having estimated how many asteroids were brighter than 19th magnitude, (1) discovered a fast moving asteroid on a Schmidt plate on June 26, 1949. It turned out to have a highly eccentric orbit whose perihelion distance was smaller than that of Mercury. It passed within 17 million miles of the sun, and within four million miles of the earth near the time of discovery (Richardson 1949, 1965). Because its perihelion distance was closer to the sun than any of the planets, Baade agreed to the name of Icarus.
It was the type of discovery that the public could understand, even if its cosmic importance did not rival the more central discoveries made soon thereafter. Nevertheless its significance for solar system astronomy and tests of general relativity soon became evident. The variations in its orbital parameters can be used to determine the mass of Mercury and the advance of the line of apsides due to space-time curvature caused by the solar mass (Herrick 1953, Gilvarry 1953, Dicke 1965, Francis 1965).
2.1.1. Stellar Evolution and Observational Cosmology
When the astronomical history of this century is written, the two central advances that will be cited 400 years from now are (1) the final understanding of stellar evolution as summarized by the HR diagram, and (2) the understanding of the universe as a whole through the development of observational and theoretical cosmology. Work with the 200-inch dominated both of these fields.
Our understanding of stellar evolution has progressed through the interaction of theoretical advances in studies of stellar interiors with the observational results concerning stellar populations, as defined by Baade (1944a, 1944b) in his resolution of the centers of M31, NGC 205, NGC 147, and NGC 185.
The population concept had crystallized in Baade's mind between 1939 and 1944, following the crucial clue provided by the discovery of globular clusters in the Fornax dwarf dE galaxy. In his many teaching sessions with H.C. Arp and this writer between 1949 and 1953, Baade was explicit in making the connection between the resolution into stars (Baade & Hubble 1939) of the main body of the Fornax dwarf and in its globular clusters. The Fornax globular clusters resolved into stars at the same apparent magnitude as the resolved stars in the main body of the Fornax dwarf itself. Thus it was natural to connect the HR diagram of globular clusters (Baade's population II) with the previously unresolved central region of M31 and also in the early type dE galaxies NGC 147 and NGC 185 whose stars were postulated to be of the same type as in the body of the Fornax dwarf.
A review of this approach by Baade to his population concept through the Fornax dwarf and then to contrasting the HR diagrams of globular clusters and of open clusters has been given elsewhere (Sandage 1986).
1 He did this following a rebuff by the IAU on the naming of an asteroid for his wife. The excuse of the name givers, following an early IAU convention, was that only Greek names could be used for asteroids, but Baade sometime in the 1930s set out to show that there were not enough Greek names to accommodate his estimate of appx.105 asteroids brighter than m = 19. Back.