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on paper torn from a notebook. It displayed the light curve for his “Variable No. 1” in M31—a roller-coaster ride that peaked at eighteenth magnitude, dipped a bit below nineteenth magnitude, and then rose once again to its maximum brightness over a period of thirty-one days, “which, rough as it is,” he told Shapley, “shows the Cepheid characteristics in an unmistakable fashion.” And here was the kicker. Hubble used the exact same technique for gauging a distance to the spiral that Shapley had devised for mapping the arrangement of globular clusters around the Milky Way. Applying the Cepheid period-luminosity formula that Shapley had derived, Hubble calculated a distance to Andromeda of around 1 million light-years (“subject to reduction if star is dimmed by intervening nebulosity,” he carefully noted). No more oblique evidence or convoluted reasoning, such as Heber Curtis was forced to use. The Cepheid provided a direct and indisputable yardstick out to the nebula. Andromeda was indeed an island universe.

Edwin Hubble's graph of the periodicity of Variable No. 1

in Andromeda, included in his letter to Harlow Shapley that

destroyed Shapley's universe (Harvard University Archives, UAV 630.22,

1921-1930, Box 9, Folder 71)

The second Andromeda variable, which Hubble had later found at the very edge of a spiral arm, was too faint for him to make a reliable distance measurement as yet. But no matter. “I have a feeling that more variables will be found by careful examination of long exposures. Altogether the next season should be a merry one and will be met with due form and ceremony,” said Hubble at the close. He was having a fine time at Shapley's expense.

Shapley, upon reading the letter, immediately grasped that Hubble's finding spelled doom for his cherished vision of the cosmos. Harvard astronomer Cecilia Payne (later Payne-Gaposchkin) happened to be in Shapley's Harvard office when Hubble's message arrived. He held out the two pages to her and exclaimed, “Here is the letter that has destroyed my universe.” Hubble was at last confirming the speculation that had been circulating through the astronomical community since the days of Thomas Wright, Immanuel Kant, and William Herschel. The Milky Way was not alone, but merely one starry isle in an assembly of galactic islands that stretches outward for millions of light-years.

Though Shapley assuredly sensed this sea change, he continued for a while to put up a good front. He mischievously wrote back that the news of “the crop of novae and of the two variable stars in the direction of the Andromeda nebula is the most entertaining piece of literature I have seen for a long time.” He wouldn't even concede that the variables were in the nebula, only “in the direction of.” He admitted that the second variable is a “highly important object” but went on to caution Hubble that his first variable star might not be a Cepheid after all, which meant it would be unreliable as a distance marker. And even if it were, he went on, Cepheids with periods greater than twenty days are “generally not dependable…[and] are likely to fall off of the period-luminosity curve.”

Hubble was undeterred by Shapley's caveats and continued his searches at a brisk clip. His discovery spurred him to find even more Cepheid variables, in both Andromeda and other spiral nebulae. But cautious as ever, he made no public announcement. Not yet.

Just a week after sending off his triumphant communiqué to Shapley, in the very midst of these cosmos-altering observations, Hubble married, a surprise to many. His bride was Grace Burke Leib, thirty-five years old and the daughter of a wealthy Los Angeles banker. A smart and petite woman, Grace had graduated Phi Beta Kappa from Stanford University with a degree in English. She had compelling dark eyes and lustrous brown hair, but a stern mouth. She was more handsome than beautiful. Grace had been previously married to geologist Earl Leib, who specialized in assaying coal deposits and was tragically killed in a mining accident in 1921. Leib's sister was the wife of