The Day We Found the Universe - Marcia Bartusiak [38]
The unforgettable nova that briefly blazed within Andromeda in 1885 had reached a brightness that could be discerned by the naked eye (just barely); the nova in NGC 6946, on the other hand, was about sixteen hundred times dimmer. Ritchey knew he had caught the nova fairly early in its burst; a plate taken just a month earlier with another telescope showed no extra speck of light whatsoever. Telegrams announcing the new find were quickly sent out to other observatories.
Curtis likely received the report with a sinking heart, for he had sighted similar novae months earlier. On the very day that Ritchey's telegram reached Lick, Curtis was actually at his desk, drafting a paper on three faint novae he had discovered in other spiral nebulae. He had been sitting on the news since March, when he first observed the flare-ups. He was being very careful, holding off any announcement until he was sure that the outbursts were not simply variable stars reaching their maximum brightness. His caution kept him from the prize of first announcement.
The first nova that Curtis spotted was in NGC 4527, an elongated spiral located in Virgo. By checking plates of this region made earlier at the Harvard, Yerkes, and Lick observatories, Curtis confirmed that no star had been visible in the spiral over the previous seventeen years. The tiny dot on his photo reached around fourteenth magnitude (some sixty thousand times dimmer than the stars in the Big Dipper). And in the course of his plate search, he came upon two additional faint novae: this time in M100 (also known as NGC 4321), a spectacular spiral in Coma Berenices viewed face-on. One of these novae had flared in 1901, the other in 1914. “That both these novae should have appeared in the same spiral is especially worthy of note,” reported Curtis. By the time Curtis announced his finds in July 1917, though, all three of these novae had completely disappeared. But he made sure to point out in his bulletin that the new stars “must be regarded as having a very definite bearing on the ‘island universe’ theory.”
With such startling news from both Mount Wilson and Lick, nova hunting spread like wildfire among the top U.S. observatories. Going to old astronomical plates and searching for novae became the craze, and new candidates were found right away. The list was getting longer week by week. “Such is the progress of Astronomy in the wild and wooly West,” joked one Mount Wilson astronomer. Curtis was tremendously excited by all the discoveries. Every time he found a new nova in a spiral, he'd go through the observatory and show off the plate, like some proud papa in a hospital maternity ward.
Curtis soon had a big enough sample of novae to make a judgment call: He suspected that the 1885 outburst in Andromeda, as well as the 1895 one in Centaurus, were rare and exceptional celestial events. Curtis guessed that their spectacular radiance had misled astronomers into thinking the novae's host nebulae had to be close by. He suggested that nova bursts actually came in two varieties: The rarer ones were big and spectacular (now known to be stars blowing apart), while the ones seen more often were less energetic (determined later to be a flaring off the surface of a white dwarf star). And since the majority of the novae being sighted in the spirals more resembled the ordinary novae seen periodically within the Milky Way, he concluded that the spiral nebulae had to be millions of light-years distant, in order for those novae to appear so dim. He said as much to the Associated Press. He boldly told its reporter that the nova bursts he had discovered occurred some 20 million years in the past, meaning the nebulae had to be 20 million light-years distant for the light to be reaching us now.