The Believing Brain - Michael Shermer [166]
“The Nebular Hypothesis Made Visible”
With this new data the pendulum was swinging back in favor of the nebulae as internal galactic structures; perhaps, some speculated, they were stars and planetary systems under development. Demonstrating the power of this concept to drive percepts, in 1888 the relatively new technology of astrophotography was introduced at the Royal Astronomical Society’s annual meeting with a dramatic photograph of Andromeda, which was declared by astronomers as “The nebular hypothesis made visible!” The mighty Andromeda was once again relegated to our galactic suburbs. Even the discovery of a nova in Andromeda, which later would be additional proof of its extragalactic origin, was reinterpreted through the lens of the nebular hypothesis as an anomaly—the very fact that it outshone the entire nebula “with the energy of some fifty million suns,” wrote one astronomer, meant that it was simply impossible that this could be an exploding star in a distant galaxy. Instead, it was suggested that it could be “the sudden transformation of the nebula into a star,” and thus the nebular hypothesis remained intact. “The question whether nebulae are external galaxies hardly any longer needs discussion,” declared the astronomer Agnes Clerke in her definitive 1890 work, The System of the Stars. “It has been answered by the progress of discovery. No competent thinker, with the whole of the available evidence before him, can now, it is safe to say, maintain any single nebula to be a star system of coordinate rank with the Milky Way.”11
At this point we would do well to remember Arthur C. Clarke’s first law: “When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.”12 As our account shifts into the twentieth century we will find that the progress of discovery supported Clarke over Clerke, beginning with an 1899 spectroscopic analysis of the Andromeda nebula by the German astronomer Julius Scheiner. Scheiner compared Andromeda to the spectra of the Orion nebula, which by then was determined to be a nearby cloud of interstellar gas. Andromeda’s spectra more closely resembled that of an enormous cluster of stars and not just a cloud of gas. To test this hypothesis, in 1908 an astronomer at the Lick Observatory near San Jose, California, named Edward Fath measured the spectra of globular clusters and noted the similarity with the spectrum of Andromeda. Game, set, and match, as far as Fath was concerned: “The hypothesis that the central portion of a nebula like the famous one in Andromeda is a single star may be rejected at once, unless we wish to modify greatly the commonly accepted ideas as to what constitutes a star.”13 But since there was as yet no accurate and reliable means to measure the distance to such celestial objects, Fath could not discern whether Andromeda represented a nearby globular cluster or a distant island universe.
“Weighty evidence in favor of the well known ‘island universe’ theory”
The final pieces of the puzzle in this celestial mystery were put together in California, first at the Lick Observatory and finally at Mount Wilson, the first two mountaintop observatories in the world that were, in their day, on the cutting edge of peering into deep space and lookback time. In the late nineteenth century, a phenomenally wealthy industrialist named James Lick, in search of the biggest and boldest monuments to which he could attach his name, pledged $1 million to build an observatory on Mount Hamilton in the Diablo mountain range just inland from San Jose. There