Completing Hubbles Work

The Hubble Deep Field and the Ultra Deep Field images would have fascinated Edwin Hubble perhaps most of all, since they plumb the depths of space near the edge of the observable universe and reveal our universe as it was 400 million years after the big bang. In current cosmological models based on the big bang, the universe has an edge in time rather than space. Looking out, we look back in time due to the finite speed of light. At the limits of Hubble’s vision, no edge in space has been detected. Rather, we’ve looked so far back in cosmic time that we’re seeing the epoch where the first small galaxies were created and began merging into the larger and mature galaxies we see around us now. The edge in time corresponds to “first light,” but beyond that was an early period called the “dark ages” when there were no stars and galax­ies. Hubble has been so successful that it has almost completed the fundamental task of seeing the entire population of galaxies in the visible universe over all cosmic time. The Ultra Deep Field images provide new information regarding how highly structured spi­ral galaxies are formed. Astronomers now understand that large spiral galaxies represent mergers, over eons, of fragments of the young, chaotic galaxies seen at the faintest levels of brightness.52 “To some degree, we can follow the stages of galaxy formation right into the fog bank of the Dark Ages and beyond, even toward the big bang itself,” writes Jeff Kanipe, who describes the Hubble Space Telescope “as both a pathfinder and a plumb line into the vast depths of our cosmic origins.”53 The Deep Field images repre­sent humankind’s first glimpse of those origins.

The Hubble Space Telescope is named in recognition of Edwin Hubble, an observational astronomer who in the 1920s and 1930s worked at Mount Wilson Observatory with the Hooker 100-inch telescope, then the largest reflecting telescope in the world. Dur­ing his lifetime Hubble was accepted as “the world’s preeminent observational astronomer,”54 in part because the 100-inch reflector allowed Hubble to seek answers to some of the then fundamen­tal questions of astronomy—whether there were galaxies beyond the Milky Way, how to create an accurate distance ladder to such galaxies, and what could be known at the limits of the observ­able universe. In 1923, Hubble determined a distance to the An­dromeda galaxy of roughly 800,000 light-years. Though today we know it lies about 2.2-2.3 million light-years from our gal­axy, Hubble’s calculation settled once and for all the debate over whether anything existed beyond the Milky Way galaxy. It was a monumental find. Hubble accomplished this through Henrietta Leavitt’s research into the regular periodicities of Cepheid variable stars. Upon discovering and charting a Cepheid variable in An­dromeda, Edwin Hubble could determine its intrinsic brightness to calculate a distance to the galaxy.55 Later, in 1929, he used the 100-inch reflector, and the inestimable skills of Milton Humason as an observer and photographer, to determine that galaxies are racing away from each other at remarkable speeds. Hubble didn’t use the phrase when he published his result, but this marked the discovery of the expanding universe.56

Perhaps it was Grace, Edwin Hubble’s wife, who dubbed him “the mariner of the nebulae.” She was an eloquent writer whose memoirs of Hubble are archived at the Huntington Library in San Marino, California. Gale Christianson’s biography, which draws upon Grace’s unpublished memoirs of Hubble, vividly recreates the scene of the astronomer at work at his telescope: “Like a captain on the bridge of a great ship, the master mariner barked out his or­ders—so many hours and so many degrees. Then came the metallic whining of the traverse, a series of loud clicks, a final heavy clang of the Victorian machinery as the 100-inch was clamped” into place for viewing far-flung galaxies, or nebulae as Hubble referred to them. Christianson extends the metaphor, characterizing Hubble as a sentinel mariner “[s]lipping, night after night, silent and alone, past the distant shoals, of the nebulae.”57 Hubble himself wrote of astronomical exploration in the terms of oceanic exploration. He spoke of the 100-inch reflecting telescope as performing reconnais­sance at the “dim boundary—the utmost limits of our telescopes,” as Hubble in the cold early morning hours would “search among ghostly errors of measurement for landmarks that are scarcely more substantial.”58

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