The Day We Found the Universe - Marcia Bartusiak [26]
From the days of Ptolemy, astronomers talked about certain stars in the sky that appeared “cloudy” to the eye. The most famous is in the northern constellation Andromeda, the mythical princess situated in the sky near her parents, Cassiopeia and Cepheus, and her husband, Perseus. At her waist is an oval patch of light, best seen on the darkest of nights. As early as the tenth century, astronomer Al-Sufi of Persia noted it as a “little cloud” in his catalog of the heavens. With the invention of the telescope more nebulae were sighted, and by the early 1700s Edmond Halley (of comet fame) counted six in all. To some observers, these pale entities were breaks in the celestial sphere, through which the light of the Empyrean—the highest heaven—came shining down. Others suggested that they were the hazy atmospheres surrounding distant stars. Halley, however, thought of them as unique celestial objects, unlike anything else in the heavens. They “appear to the naked Eye like small Fixed Stars,” he wrote, “but in reality are nothing else but the Light coming from an extraordinary great Space in the Ether; through which a lucid Medium is diffused, that shines with its own proper Lustre.”
Gradually found in greater numbers, these celestial objects took on even more importance in 1781 when the celebrated comet hunter Charles Messier published in France his list of more than one hundred nebulae, a directory that is still used today. The Andromeda nebula, for example, is commonly known as M31 because it's the thirty-first nebula in Messier's catalog. Messier, though interested in the nebulae themselves, primarily wanted to let his fellow observers know that these celestial regulars, the most prominent of their kind, should not be mistaken for comets. He was putting up cosmic road signs for his colleagues, pointing out those nebulae visible above the horizon from the latitude of Paris.
No one was more excited by Messier's list than William Herschel, England's soon-to-be crown prince of astronomy. As soon as Herschel received a copy of Messier's catalog, he immediately aimed a telescope at the celestial clouds. “I…saw, with the greatest pleasure, that most of the nebulae, which I had an opportunity of examining in proper situations, yielded to the force of my light and power, and were resolved into stars,” he wrote a few years later. He was the first to make this discovery, using a telescope twenty feet in length with a mirror then twelve inches wide. It was the most powerful in its day, allowing him to see that many of the nebulae (what we now call open clusters and globular clusters) were actually comprised of hundreds and thousands of stars. This led him to the belief that all nebulae were far-off systems of stars. Any nebula still appearing cloudlike through his eyepiece, he figured, was simply too distant to behold individual stars clearly.
Herschel promptly initiated a grand hunt for nebulae, literally sweeping the heavens with his giant reflector. Previous endeavors to spot nebulae paled beside this effort. By 1786 he had sighted a thousand new nebulae and star clusters; three years later he added hundreds more. “These curious objects, not only on account of their number, but also in consideration of their great consequence, [are] no less than whole sidereal systems,” he wrote. He even boasted at one point that he had discovered fifteen hundred new universes. Each, he excitedly reported, “may well outvie our milky-way in grandeur.”
Herschel had come late to this pursuit. Raised in the Duchy of Hanover (now part of Germany) within a family of musicians,