Shapleys Scientific Record
In 1920 a debate on The Scale of the Universe took place between two astronomers, the older and respected Heber D. Curtis, and the young and ambitious, but little known, Harlow Shapley.(1) Curtis argued that the many spirals and nebulae visible through telescopes are galaxies or universes outside the Milky Way, which with its billions of stars is but another nebula to a viewer from a distant galaxy. Shapley argued that the solar system is located in an off-center position in the Milky Way, but that the Milky Way is the only galaxy in the entire universe, the spirals and nebulae being some nebular formations on its periphery.
A. Pannekoek described the position taken by these two astronomers in this way:
It is known today that there are many billions of galaxies in the Universe, not just the one galaxy of the Milky Way, as Shapley argued. He also grossly overestimated the size of the Milky Way, assessing it at 100,000 parsecs. The figure is certainly too large,(3) as Pannekoek notes.
Forty years later Otto Struve concluded an article describing that debate thus:
This seems to be said with tongue in cheek, because hardly anyone would justly evaluate the outcome of the debate as a draw. Shapleys claim that there exists only one galaxy, the Milky Way, whereas it is known that billions or hundreds of billions of galaxies like the Milky Way exist, is a much greater deviation from the truth than Curtis misjudging of the non-central position of the solar system in the Milky Way. Nevertheless, exploiting the fact that Curtis soon died, Shapley was left to claim the victory for himself and the story was worked up to his having been a second Copernicus: as Copernicus had demonstrated that this world of ours is not in the center of the solar system, so Shapley was said to have demonstrated that our solar system is not located in the center of the galaxy, but more toward the periphery. Several times I read and heard this proclamation being made on Shapleys behalf. Once it was on television, said so in his presence, and he basked in the halo of a genius before the multitudes of viewers.
The actual picture that emerges from this debate is a far cry from the story familiar from books, articles, radio and television, which repeats the same theme that while Copernicus discovered that the Earth is not in the center of the solar system, Shapley discovered that the Solar System is not positioned in the center of the Milky Way. Such a story gives Shapley credit for a discoveryand victory in the debateboth of which were undeserved.
Not even the claim that the solar system is located off-center in the Milky Way can be credited to Shapley. Immanuel Kant in his Universal Natural History and Theory of the Heavens (1755) wrote: But perhaps it is reserved for future times to discover hereafter the region at least where is to be found the centre of the system of the fixed stars to which our sun belongs. . . .(5)
Kant observed that the zone of the Milky Way is broadest in the part that lies between the constellations of the Swan and Sagittarius,(6) and offered the surmise that this will be the side where the place of our sun is nearest the outermost periphery of the circular system.(7)
Moreover, Kant realized that the Milky Way is not the only galaxy. He wrote:
Kant cited as a source for some of these views Mr. Wright of Durham, an Englishman.
As for Shapley, in the years following his debate with Curtis, he did not produce any work of importance, and this was also pointed out in the literature. Forty-five years later he persistently claimed this great discovery as his own accomplishment and triumph.(9)