Making improvements in fits and starts—three steps forward, two back—Keeler and his associates at last got the telescope operating tolerably in September 1898, just four months after he arrived back at Lick. On the fifteenth of that month he tried out his camera for the first time. His opening target, Altair, the brightest star in the constellation Aquila, was out of focus, but another exposure, east of the star, was better. “The fainter stars look pretty sound, but the brighter ones show irregularities,” he wrote down in his logbook. Two weeks later he took a photograph of the Moon, then nearly full. “Plates are fairly good,” he briefly noted. Inside the Crossley dome, the upper wall was painted black, in order to absorb stray reflections from the sky; the lower half, though, was colored bright red, so Keeler and his assistants could see where they were going in the dark. The whole interior was bathed in the faint glow from a lantern fitted with panes of crimson glass, as the photographic plates were not sensitive to red light. Such precautions were essential since the Crossley mirror was held by an open framework of iron rods instead of mounted within an enclosed tube.
In late fall Comet Brooks appeared in the sky. This led to Keeler's first research paper based on his observations with the Crossley. His images, taken over eleven consecutive nights with the help of his assistant Harold Palmer, displayed finer details than previous photographs of comets. They even captured a double nucleus. “On the negative of November 10, obtained with an exposure of 50 [minutes],” reported Keeler, “the head of the comet is made up of two clearly separated nebulous masses, surrounded by the nearly circular coma…. I am inclined to believe that the division of the nucleus was real.” Keeler was not the first to discern such cometary structure, but it was exciting nonetheless.
He soon was observing the Pleiades, the impressive cluster of stars (the “Seven Sisters”) situated near the constellations Taurus and Orion in the autumn nighttime sky. Taking a series of photographic exposures, sometimes lasting longer than an hour, he was able to show that the Pleiades is embedded in filamentary and diaphanous clouds of gas. “Nebulous wisps…are characteristic of the region,” he reported. He later wowed astronomers with a spectacular photograph of the Orion nebula, convincing them of the capability of a reflecting telescope to bring out features formerly too faint to discern. The stunning image served as the frontispiece for an issue of the Publications of the Astronomical Society of the Pacific, and it amazed even him. “The photographic power of the Crossley reflector on a fine night is surprising,” he wrote, “at least to one who has hitherto worked with refractors only.”
Keeler went on to use the Crossley to record other arresting celestial sights, such as the sinuous and radiant strands of the Lagoon, Omega, and Trifid nebulae. “We know them so well today,” Osterbrock pointed out, “that it is hard for us to realize how sensational his photographs were to the astronomers of his time… They showed much more detail than even the best drawings of the earlier visual observers.” Keeler was generating the Hubble Space Telescope pictures of his time.
Outside his duties as Lick director, Keeler was spending all his available time on Ptolemy Ridge, becoming the world's expert on nebulae. “The [Crossley's] workmanship is poor and the design is clumsy, but on a fine night the photographic power is quite extraordinary. It has seemed to me worth while to devote some time to ordinary photography of nebulae, as nothing that I have yet seen in this line comes up to what I can get with the Crossley,” he told a friend.
The week before and the week after the new Moon, when the lunar orb was in inky shadow, were his best viewing times. Only then was the sky dark enough to photograph the faint nebulae he was beginning to detect, without interference from a bright lunar spotlight. When the night was clear and calm, he often had time to take several exposures. But then there would be stretches, even when the sky was cloudless, when the wind was so strong that the Crossley shook on its mount, ruining his observation.
Keeler at last got around to his first spiraling nebula on April 4, 1899. He started off with one succinctly named M81, situated in the constellation Ursa Major, just above the “pot” of the Big Dipper. He carefully tracked it from nine until eleven o'clock that evening, as two hours were needed to gather enough light to record an image on the plate. Once the plate was developed, he right away noticed a faint spiraling but considered it “valueless.” A misalignment of the telescopic axis had unfortunately led to the stars appearing as small arcs.
His luck was better the following month. With the Crossley fixed, he took several photos of M51, known as the Whirlpool for its wondrous view of the spiraling, face-on. Keeler's four-hour exposure captured aspects of the nebula never before seen, largely due to the steady air above Mount Hamilton. Keeler sent a transparency of this exposure to his friend George Ellery Hale, director of the Yerkes Observatory, where it took Hales breath away. “Everyone in the Observatory considers [this picture] to be far superior to anything of the kind they have ever seen or expected to see,” Hale responded enthusiastically.
There was something even more consequential in the image, although Keeler didn't appreciate the import right away. Surrounding M51 in the picture were seven more nebulae—though smaller and fainter. In a brief note to the Royal Astronomical Society in London, he listed the exact locations of these nebulae and described them. Some were round, others spindle-shaped or elongated. And that was only the beginning. “Several other faint nebulae, the positions of which were not noted, were observed during the search,” he wrote. “In fact, this region seems to be filled with small, apparently unconnected nebulae, large numbers of which would doubtless be revealed by long-exposure photographs.” It was a fascinating find, but he just assumed it was an uncommon grouping of nebulae, likely confined to that sector of the sky.
Photo of Whirlpool galaxy (M51) taken by James Keeler in 1899 with the
Crossley telescope. One faint nebula seen in upper left.
(Copyright UC Regents/Lick Observatory)
When a selection from Keeler's growing archive of pictures was prominently displayed at the Third Conference of Astronomers and Astrophysicists, held at Yerkes in September 1899, it created great excitement. Astronomers formerly skeptical of a reflector's value, such as E. E. Barnard, began to change their opinion. Barnard, who had fled from Lick to Yerkes during the Holden debacle, just stood in front of Keeler's photographs for hours, taking in every scrumptious detail of the Orion nebula, the Pleiades, and the M51 spiral.
Media savvy, Keeler knew the value of a good pitch in helping both the observatory and his career. After a well-publicized solar eclipse, he had advised a fellow astronomer, who was about to convey his eclipse observations to a conference, to dwell “on the successes rather than on the failures. If you were to tell a reporter that three plates out of ten were failures, he would receive a totally different impression from what he would if you gave him the equivalent statement that seven out of ten plates were successes.” Keeler sent copies of his best pictures to the Royal Astronomical Society, the New York Academy of Sciences, and the American Philosophical Society in Philadelphia, all institutions that could influence opinions within the scientific community. He also made sure that Crossley, the reflector's former owner, received a particularly nice print of the Orion nebula. “The finest I have ever seen,” replied the English businessman. “It proves to me how important it is not only to have a powerful instrument but also a site where it can be used to the greatest possible advantage.” Getting his results widely distributed seems to have paid off for Keeler. In 1900 he was elected to the National Academy of Sciences, a year after he had received its prestigious Henry Draper Medal for astrophysical research. He was now one of America's leading astronomers.
In late summer, right before the Yerkes conference, Keeler had started to examine the faint nebulae more closely. He took a one-hour exposure of NGC 6946, a fuzzy patch first noticed by astronomer William Herschel at the end of the eighteenth century and listed as the 6,946th object in the New General Catalogue,
published by J. L. E. Dreyer in 1888. Upon developing his plate Keeler saw immediately that it was yet another spiral, similar to M51 and M81 but smaller in size. A few nights later he examined two more fuzzy nebulae. Again he found, in each case, spiraling arms wrapping around a brightened center. All these dim nebulae appeared to be flattened disks, much like the Andromeda nebula, but they were set in different orientations.
And something more surprising developed as this work progressed. Each time Keeler took a photograph, he found even fainter nebulae loitering in the background of his image. At the start of his venture, when he first saw the seven nebulae on his plate of M51, he thought it “a rather remarkable number of nebulae to be found on a plate covering only about one square degree.” That's a segment of the sky the size of two full Moons. But he soon discovered that this celestial flock wasn't so remarkable after all. With each additional picture Keeler took, he detected more and more nebulae arrayed over the heavens. Throughout the fall of 1899, whenever the nighttime sky was clear and moonless, he made his way to the Crossley and kept adding to his count. He took a four-hour exposure of NGC 891, a spiral seen edge-on, and the plate revealed thirty-one new nebulae, scattered around the central spiral like background extras in a movie scene. On a photograph of NGC 7331 he saw twenty more and “there are nearly as many on several other plates,” he reported. “Besides these new nebulae…the plates contain a considerable number of objects which are probably nebulae so small that the resolving power of the telescope is insufficient to define them in their real form and to bring out their true character.”
Keeler was dumbfounded. Space was awash with tiny nebulae, and most of them displayed a conspicuous spiral form, though seen from assorted angles. “There are hundreds, if not thousands, of unrecorded nebulae within reach of our 36-inch reflector,” reported Keeler. By assuming that there were three new nebulae in each square degree (a number he admitted was far too conservative), he estimated that “the number of new nebulae in the whole sky would be about 120,000.” He was positive there were more. Before this, about nine thousand nebulae had been cataloged by astronomers but only seventy-nine were identified as spirals, less than 1 percent. The Yerkes Observatory, in Wisconsin, by then had opened to great fanfare with a bigger telescope, one with a lens forty inches in width, but it still could not compete with Keeler's reflector. Even Barnard conceded that his new home at Yerkes, situated at a more lowly thousand feet above sea level, was “a mirey climate for a great telescope and discoveries are few and far between.”
Keeler's 1899 image of NGC 891 with background nebulae marked
(Copyright UC Regents/Lick Observatory)
In an article in Astronomische Nachrichten, a highly respected German astronomical journal, Keeler drew attention to his baffling finds: “The spiral nebula has been regarded hitherto as a rara avis—a strange and unusual phenomenon among celestial objects, to be viewed by the observer with special interest, and marked in catalogues with exclamation points… But so many other nebulae also proved to be spirals that the classification…soon lost its significance… The same form occurs over and over again, on a smaller scale, among the fainter nebulae.” Spirals were now the norm, not the exception, in the celestial sky. Keeler figured they must be an important constituent of the universe, ranging in size “from the great nebula in Andromeda down to an object which is hardly distinguishable from a faint star disk.”
But what in blazes was a spiral nebula? No one knew for sure, solely because there was as yet no way to determine the distance, a recurrent problem for astronomers. If the spirals were nearby, part of the Milky Way, then they would be relatively small given their size in the sky, each possibly a new star forming. But if the spiraling patches were very far away, then they would have to be huge to appear as they did in telescopic photographs, as big as the Milky Way itself.
To Keeler, the whirling shape seemed to indicate that the object, whatever its nature, was rotating. And like many of his contemporaries, he speculated that the spirals were somehow linked to star formation. “If…the spiral is the form normally assumed by a contracting nebulous mass,” he pondered, “the idea at once suggests itself that the solar system has been evolved from a spiral nebula.” Given this view, each spiral then marked the spot where a new star and its planetary companions were hatching. The idea that our solar system condensed out of a rotating nebula of gas had already been introduced by both Immanuel Kant and Pierre-Simon de Laplace decades earlier. In a lecture at Stanford University, Keeler made this very point: “The heavens are full of beautiful illustrations of the views of Laplace…[in] photographs of great spiral nebulae in various stages of condensation, taken recently with the Crossley reflector at the Lick Observatory.”
Much as Einstein's relativity inspired numerous works of art and literature since its inception, so too did the nebular theory in the nineteenth century, as seen in this stanza from “The Princess,” by Great Britain's poet laureate Alfred Lord Tennyson in 1847:
This world was once a fluid haze of light,
Till toward the centre set the starry tides,
And eddied into suns, that wheeling cast
The planets …
It's interesting to contemplate how far Keeler might have gone in this line of research. With his phenomenal skill at the telescope, he had a good shot at obtaining spectral data that forced him to consider other explanations for the nature of the spiral nebulae. “Keeler…was a far better trained, more experienced spectroscopist than any [other astronomer of his time]. No doubt he would have reached the conclusion that the spirals were galaxies of stars,” contends Osterbrock, himself a Lick Observatory director seven decades after Keeler. Keeler might have also noticed, far earlier than others, that the spirals were racing away from the Milky Way at high velocities. He had the smarts, and he had the equipment. He had already obtained the velocities of myriad planetary nebulae and had a plan to move on to the spirals. His friend Hale had that impression; he was sure that Keeler intended to “follow up his remarkable beginnings with the Crossley reflector, cataloging the new nebulae, and doing something with their spectra.”
But we will never know, for Keeler died unexpectedly on August 12, 1900, one month shy of his forty-third birthday. Throughout the spring and summer of 1900 Keeler had been suffering from what he called “a hard cold.” An entrenched cigar smoker since his college days, he had already been experiencing heart problems. His doctor also diagnosed pleurisy of the lung, “nothing very serious,” Keeler told friends, but he was likely afflicted with either emphysema or lung cancer. He couldn't manage walking the steep rise from the Crossley reflector back to his home without stopping several times short of breath. With his doctor forbidding him to continue observing, he left the mountain at the end of July for a short rest with his family. He was expecting to return to use a new spectrograph, just completed for the Crossley, and begin examining spiral nebulae. But within weeks Keeler died in San Francisco, after experiencing two strokes. The setback for astronomy, said his friend and colleague Campbell, was “incalculable.” Harvard College Observatory director Edward Pickering wrote that the “loss cannot be overestimated… There was no one who seemed to me to have a more brilliant future … or on whom we could better depend for important advances in work of the highest good.” The journal Science ran a tribute to Keeler on the first page of its September 7, 1900, issue.
On Mount Hamilton, the memory of Keeler became sacrosanct and remains so to this day. He was the ideal director, an astronomer without equal cut down in his prime. But Keeler's acclaimed reputation beyond the Lick Observatory grounds gradually faded. In encyclopedias he is primarily remembered (if he is mentioned at all) for his work on Saturn's rings, with only a brief reference to his pioneering use of a reflecting telescope at high altitude, which allowed him to record the myriad spiral nebulae. Yet his tenacious pursuit of the nebulae with the Crossley reflector is truly his most lasting legacy. “The day of the refractor was over,” said Osterbrock, “and altho
ugh a few more intermediate-sized ones were built, no American professional astronomer ever thought seriously of building a very large telescope as anything but a reflector, after Keeler's work with the Crossley.”
With his innovative spirit and success in restoring a once-despised instrument, Keeler pushed reflectors to the forefront of astronomical research. Campbell, who had been carrying out his program to map the motions of the stars, knew that Lick needed a second telescope in the southern hemisphere to complete the observations. Chosen as Keeler's successor to the directorship, he decided to build another 36-inch reflector, similar to the one that Keeler so successfully got working. In 1903 this telescope was erected on a site outside Santiago, Chile, where it was in operation for twenty-five years. The refractor at Lick had cost hundreds of thousands of dollars; Campbell built his Chilean scope for a thrifty $24,000.
In the fall of 1901, just a year after Keeler's death, the Yerkes Observatory assembled a trial reflector of its own in one of its small domes. With a mechanical system far superior to the Crossley, which allowed the mirror to be highly stable, this Yerkes reflector yielded photographs of nebulae that were even better than Keeler had obtained, despite its smaller 24-inch aperture. “The results obtained with the two-foot reflector show that very fine atmospheric conditions are necessary for the best results,” reported the telescope's builder, George Ritchey. “It is interesting to think of the photographic results which could be obtained with a properly mounted great reflector in such a climate and in such atmospheric conditions as prevail in easily accessible parts of our country, notably in California.”
The Day We Found the Universe Page 5