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D. E. Osterbrock (UCO/Lick Obs.,UCSC)
Walter Baade discovered the two stellar populations with the 100-in Mount Wilson reflector during World War II, but applied, tested, and extended this concept with the 200-in Hale telescope after it went into operation on Palomar Mountain in 1949. But he had begun observing there with the 18-in Schmidt telescope in 1937, soon after it was completed. Baade used panchromatic films and deep red filters in an attempt to penetrate the heavy interstellar extinction toward the Galactic center. The extinction was much too heavy for him to observe the center, but he found the least obscured regions in this survey, including "Baade's window," and several highly obscured globular clusters.
The 48-in Schmidt was completed in 1948, and Baade was one of the very few observers allowed to use it briefly, before all the observing time was turned over to the National Geographic-Palomar Observatory Sky Survey. Again, he concentrated on seeking the "clearest" regions near the Galactic center, and also obtained some pictorial photographs of nebulae to publicize the success of the new instrument.
Especially after Edwin Hubble's first heart attack in 1949, Baade took most of the final test exposures which Ira Bowen used to analyze and tune up the shape of the 200-in mirror. After the Hale telescope was in full operation, Baade had the lion's share of observing time with it. He had been aching to use it to search for RR Lyrae variables in M 31 it, and not finding any confirmed Baade's well grounded conjecture that the distance scale in use then was wrong. His work on variable stars in M 31, on the polarization of the continuum of the Crab nebula, and with Rudolph Minkowski on the optical identification of radio sources are a few examples of what he did with it. These and several other programs will be described, along with some of Baade's other activities at Palomar.