The Day We Found the Universe - Marcia Bartusiak [64]
Shapley ultimately took Bailey's advice and, starting with the variables found by his wife, placed a firm stake in this domain. Shapley and globular clusters quickly “became synonyms” atop the mountain. Shapley's involvement became so intense that he eventually contacted Bailey, to make sure the Harvard astronomer didn't feel Shapley was trespassing on his celestial territory. “I have not intended to intrude upon your field, and I think that you do not feel that I am,” wrote Shapley. “Very much of my work on clusters has been the direct result of my conversation with you in Cambridge three years ago when you suggested the advantages of the Mount Wilson instruments and weather.” Bailey, a kind and gracious man, was in fact delighted by Shapley's joining in. “I hope you will appreciate the fact that I claim no proprietorship in these clusters,” replied Bailey, “but… welcome other investigators in this field.” It was fortunate that he was so affable. Bailey was primarily a data gatherer; Shapley by nature was a bold interpreter, a trait enhanced during his apprenticeship with Russell, who advocated problem-driven research. And that made all the difference in advancing the science.
A globular cluster appears through a telescope as an assembly of brilliant specks of light hovering around a dense and blazing core. With stars packed in like subway commuters at rush hour, the cluster offers a far more exotic celestial environment than our local stellar neighborhood. Alpha Centauri, the star closest to the Sun, is some 4 light-years away. But if the Sun were in the center of a packed globular cluster, it would have thousands of stars closer than that, covering Earth's sky like a sequined blanket visible both day and night. Near misses between stars would be commonplace.
That a globular cluster is a highly spherical collection of stars was not known until the 1600s, with the advent of the telescope. Before that, ancient astronomers simply noted the objects on their sky charts as a “lucid spot” or a lone “hazy star.” Today, these clusters are known to be arranged as a globelike halo, surrounding the disk of the Milky Way somewhat like bees buzzing around a hive. But as late as the 1910s, when Shapley began his observations, astronomers didn't know that, nor exactly how big an individual globular cluster was. Some even pondered if they were island universes in their own right. Shapley himself believed that was true when he was starting out: “It is quite obvious that a globular cluster … is in itself a stellar system on a great scale—a stellar unit which without doubt must be comparable to our own galactic system in many ways,” he wrote in the first paper of his study. Some dabbled with the idea that a spiral nebula was an early stage of a globular cluster about to form: Like an open flower closing at twilight, the spiral over time would fold up into a ball. Shapley's goal was to learn the globulars' true sizes, distances, and compositions and see if such ideas were valid.
Shapley's initial observations were fairly basic. Using the 60-inch telescope, he simply surveyed the colors and magnitudes of the stars in the most prominent clusters. These included Omega Centauri (the biggest of them all), the Hercules cluster, and M3, a globular noted by Charles Messier in 1764. Shapley had no idea where this would lead, but that was standard practice in astronomy: Gather as much data as you can when faced with the unknown and keep your eye out for unusual trends. If anything,