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By Root 468 0

” 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