Annu. Rev. Astron. Astrophys. 1999. 37: 445-486 Copyright © 1999 by Annual Reviews. All rights reserved

1. THE BEGINNING

The 200-inch Palomar reflector, shown in the famous drawing by Russell W. Porter in Figure 1, was commissioned for regular scheduled observations on November 12, 1949, fifty years to the month of the distribution of this volume of Annual Reviews. The Hale telescope, planned since 1929, had enormous publicity surrounding both its construction and the hopes for astronomy as to what it might accomplish. The purpose of this review is to discuss the extent to which those hopes have been realized. Palomar, together with Mount Wilson in the joint operation known at first as the Mount Wilson and Palomar Observatories, often lead the way in the explosive developments that have characterized astronomy in the period.

Figure 1. Drawing by Russell W. Porter of the 200-inch telescope and its dome made in 1936. Note the roller bearings at the north pier, replaced in the real telescope by the oil-pad flotation invention. Note also that the girders of the dome structure are not covered here as they are in the dome. The dome was finally completed with a double sheathing for thermal control.

A scientific dedication took place a month later during the joint meeting of the Astronomical Society of the Pacific and the American Astronomical Society (Richardson 1948). The principal scientific address was by Walter Baade (1948) titled "A Program of Extragalactic Research for the 200-inch Telescope." This was a prescient document, outlining a research program that was to take 30 years. Much of Baade's lecture will be discussed later.

The telescope was not released to the astronomers for another 16 months. Ira Bowen (Figure 2), hero of that period and for the following two decades, keeping his head when all others were losing theirs, knew that if he released the telescope to the astronomers, even for a few months, he would never get it back. As director and as one of the world's foremost experts on optics, he was responsible for bringing the telescope to as high a state of perfection as the design of the engineers permitted.

Figure 2. The leading players in the early days of stellar evolution and cosmology at Palomar. Left to right, top to bottom: Ira S. Bowen, Walter Baade, Edwin Hubble, Milton Humason, Rudolph Minkowski.

By 1948, two problems had surfaced (Bowen 1948, 1949). (1) The lever system that grabbed the honeycomb ribbings at the back of the five-meter mirror had too much friction by a factor of 30 to keep the mirror at its proper figure for all gravity loadings. (2) As it left the optical shop, the mirror had a slight turned-up edge, purposely, so that its sag in the cell beyond the radius of the back squeeze levers was expected to compensate for the raised outer 20 inches. But the mirror did not compensate as was predicted. It was too stiff.

Thus, Bowen made the very difficult decision to take the mirror out of the telescope and polish down the turned-up edge on the dome floor. The final figuring of the outer raised 20 inches was done by Don Hendricks, the chief optician of the Mount Wilson observatory who had a magical touch, together with Mel Johnson, one of the opticians who had originally worked on the mirror from 1936 to 1946 in the Caltech optical shop (with four years out for World War II).

A long series of optical tests were made after this fix and were analyzed by Bowen from measurements on the Hartmann test plates. They revealed that the mirror was nearly perfect. The matter-of-fact description of these trying tests and his initial decision to remove the mirror for the fix is described by Bowen (1950) in a classic paper entitled "Final Adjustments of the 200-inch Telescope." He had waited to publish this account until Hubble (1949) had written an account called "First Photographs With the 200-Inch Hale Telescope" in which Bowen is not mentioned, yet the needed mirror correction is discussed as if the photographs had first revealed the problem. However, the first photographs had in fact been taken by Bowen with the telescope, months before, as part of the testing regime. As great an astronomer as Hubble was, he could never overcome his disappointment that he had not been chosen as the director of Palomar.

Nevertheless, Hubble's fame, importance, and close association with the 200-inch project through cosmology, which in some sense justified its construction following his seminal discoveries at Mount Wilson from 1922 to 1936, were the reasons he was given the opportunity to use the telescope in four observing runs between January 1949 and April 1949, interspersed with Bowen's Hartmann-testing regime.

The first scheduled run in which the telescope was officially assigned to an astronomer was on November 12, 1949. That observer was not Hubble. He had suffered a heart attack in June 1949 before the completion of Bowen's extensive work.

As important as the 200-inch reflector has been for astrophysics and cosmology, the Palomar wide field 48-inch Schmidt survey telescope was in some ways as important in the early years for mapping the northern hemisphere sky. That era is so long ago that it is difficult to remember the state of our ignorance of the deep sky before the Palomar Schmidt Survey. As it turned out, without that mapping, the 200-inch would have been vision impaired.

The primary 72-inch mirror for the big Schmidt had been completed by 1941 in the Mount Wilson optical shop. The difficult 48-inch correcting plate, ground and polished to its non-spherical figure by Hendricks, was completed in the summer of 1948 and the telescope went into routine operation in January 1949 (Bowen 1948). Walter Baade had been instrumental in bringing the principle of the Schmidt optical train back from Hamburg in the early 1930s, having been a colleague of Bernhard Schmidt, a taciturn Estonian, in the late 1920s when Baade was still on the staff of the Hamburg Observatory. They had been members of the Hamburg eclipse expeditions to Lapland in 1927 and the Philippines in 1929, and were close friends.

The first official Schmidt plate (recorded in the record book on September 29, 1948) was taken by Hendricks, who was in charge of the completion of the optics and collimations of the telescope. The 14-by-14-inch plate was of M31, seen for the first time on a single plate with superior definition and faint limiting magnitude in its full 4° extent. A reproduction of the Hendricks' plate is in Panel 18 of the Hubble Atlas (Carnegie Publication No. 618). The first published photographs from the 48-inch Schmidt were by Minkowski (1949) who showed them in his description and analysis of the nebula surrounding the young galactic cluster NGC 2244.

Four wondrous books on Hale and the making of the Hale telescope, of Palomar itself, and of its predecessor observatories of Yerkes and Mount Wilson are The Glass Giant of Palomar (Woodbury 1940), Explorer of the Universe: A Biography of George Ellery Hale (Wright 1966, 1994), Palomar: The World's Largest Telescope (Wright 1952), and The Perfect Machine (Florence 1994).