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

5.1. Large-Scale Distribution

Hubble had dreamed of beginning at Palomar a galaxy count program of the type he had pioneered in the 1930s (Hubble 1934). The data had formed the basis of his work with Tolman on world models (Hubble & Tolman 1935) and his famous analysis papers (Hubble 1936a, b) on the log N(m) relation (see Sandage 1998b for a review). To this end he began to accumulate plates in the spring of 1949 for galaxy counts with the 48-inch Schmidt camera. The very large 14-by-14-inch plates had exquisite definition over a 7° × 7° field compared with the Mount Wilson large reflector plates that covered only 0.25 square degrees which Hubble had used for the 1934 study.

My first association with Hubble and the research part of Mount Wilson and Palomar was as a summer assistant in 1949 in measuring the plates and beginning the galaxy counts. The program was not continued for several reasons, one of which was Hubble's heart attack in July 1949, and another was the press of the more urgent programs that Hubble had set out.

It is fortunate that the count program did not become a central project at Palomar because it would not have been carried to the necessary conclusions to have made a major contribution. Hubble acknowledges this in his Penrose lecture, stating:

"The distribution of nebulae over the sky is not included in the Palomar program. Such an investigation is being carried on at the Lick Observatory by counting the nebulae on survey plates with the fine 20-inch camera which in time will cover the entire sky observable from that latitude. [The program by Shane and Wirtanen] will present the distribution of more than a million nebulae to about 18th magnitude. The data will test the current assumption of large-scale uniformity over the sky ('isotropy' or 'no favored direction') and will describe the small-scale distribution, or tendency toward clustering."

Indeed, the Lick survey did just that (Shane 1975).

The program on the large-scale distribution, although not done at Palomar, is central to modern cosmology and includes the early papers by Seldner et al (1977), Gregory & Thompson (1978, 1982), Chincarini & Rood (1979), Tarenghi et al (1979), with reviews by Oort (1983), Rood (1988).

A most important survey of galaxy distribution that was done at Palomar and that has had a lasting influence on observational astronomy is the catalog of galaxy clusters by Abell (1958, 1975). Abell's survey was made using the 48-inch Palomar Observatory-National Geographic Sky Survey plates (POSS) as his Ph.D. thesis from the California Institute of Technology, under the direction of Rudolph Minkowski, director of the Sky Survey. More will be said about this important Abell catalog in the next sections, but before leaving the large-scale distribution problem, it should be pointed out that Abell, already in 1959, anticipated the discovery of the filaments, sheets, and voids, which are now known to be present by his first identification of what he called superclusters, or clusters of clusters.