The Day We Found the Universe - Marcia Bartusiak [106]
Hubble's observations at this time were fairly routine as he methodically went from target to target. He was noted for carrying a map of the heavens in his head; the hundred-odd Messier objects were as familiar to him as the alphabet. On July 17 he stopped to confirm a new and wispy nebula that Shapley had reported seeing on two occasions earlier that year in the Boötes constellation. But even after a 150-minute exposure, Hubble came up empty-handed. He saw nothing in that area of the sky. “Shapley object is probably an accident,” wrote Hubble in his logbook. From a photo he took on August 15, he spotted the track of an asteroid passing by. Week by week the routine continued.
And then came the October surprise.
Discovery
Countless Whole Worlds…
Strewn All Over the Sky
October 4, 1923. The seeing was poor, but it was good enough (just barely) to stalk some celestial quarry that autumn evening. Hubble first pointed the 100-inch at NGC 6822, the far-off, Magellanic-like cloud of stars that he had long been studying. As the giant scope swung around, there was a whine, a series of loud clicks, and then a final clang as the instrument was secured into place. After taking an hour-long photographic exposure, Hubble went on to examine M32, a small and roundish nebula, for a spell. He then maneuvered the telescope just a fraction of a degree to photograph M31—the famous Andromeda nebula, the target of choice in the island-universe debate. By then the seeing had deteriorated to a point that other astronomers might have closed up shop. But Hubble persevered, and despite the mediocre viewing, soon noticed a new speck of light within Andromeda's cloudy veil. It was exactly what he was hoping to find one day as he conducted his extensive survey of the nebulae. Novae had been seen before in Andromeda; that wasn't startling. But Hubble was sure that additional sightings would help reveal Andromeda's secret. “Nova suspected,” Hubble neatly wrote in black ink in his logbook for Plate H 331 H. After photographing Andromeda for forty minutes, he went on to observe another nebula, a barred spiral, before ending his run.
The very next night Hubble returned to the 100-inch to follow up. This time the atmosphere was better—clear and steady, at least for a while. When the sky was at its best, he aimed the telescope at Andromeda and again saw the new pinpoint of light. “Confirms nova suspected on H 331 H,” Hubble noted in his logbook.
Everything, though, cannot be readily seen through the telescopic eyepiece or by a quick peek at a newly developed photograph. Plate H 335 H, the forty-five-minute exposure taken on October 5 to verify the nova, was analyzed in more detail later, back in Hubble's Pasadena office. There he confirmed not just one but rather three new pinpoints of light within Andromeda. He figured he was seeing two additional novae and wrote “N” beside each one on his plate to mark their location.
From his earlier work on the Magellanic cloud–like NGC 6822, Hubble knew that he had to make sure his newly spied objects were truly novae and not some other phenomenon. For a further check, he turned to the massive collection of plates archived in a quakeproof vault at the observatory headquarters. He began perusing previous photos of the Andromeda nebula, taken by observatory astronomers as far back as 1909. By comparing his latest photographic plate with those from the past, he could easily see that two of his spots of light were indeed novae—never-before-seen stellar flares. But one spot, the one farthest out from the center of the nebula, had been around before. Going from plate to plate, Hubble could see that this tiny dot of light was brightening and dimming over