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Home , Edwin Hubble, Harlow Shapley, Henrietta Swan Leavitt, Mount Wilson Observatory

National Aeronautics and Space Administration

Age of the : Size of the Universe: 2 Billion Years Cosmic Times 280 Million Light Years 1929 Andromeda Lies Universe is Expanding “” Resolved Dr. Hubble’s discovery settles the “Great “Red Shift” is Proof of Einstein’s General Theory Debate” over the size of our own and the distance to, and nature of, spiral Outside Milky Way Galaxy Using the 100-inch Hooker at Although Hubble’s work presents a tremen­ nebulae. Mount Wilson , Dr. Edwin Powell dous breakthrough in our understanding of the Held on April 26, 1920 at the National Acad­ Spiral Nebulae are indeed “Island ” Hubble has studied a variety of spiral nebulae universe, one big question remains. How far out emy of in Washington, D.C., the de­ and established that they are moving away from into the universe does his model hold? The 100­ bate focused on the opposing views of astrono­ us at a rapid pace – strong evidence of an expand­ inch telescope can resolve Cepheids in only the mers Dr. of the Mount Wilson ing universe. He has further determined that the nearest nebulae. In nebulae where Cepheids are Observatory and Dr. Heber D. Curtis at the Uni­ speed of increases with greater distance. barely visible, Hubble has identified the most versity of California’s Lick Observatory. Hubble and his colleague Milton Humason luminous individual , some 50 to 100 times Shapley’s studies had led him to a concept of measured the radial velocities and distances of brighter than the Cepheids. He uses these lumi­ the Milky Way as an enormous galaxy of stars twenty-four of these nebulae. Because they are nous stars as standard candles for more distant some 300,000 light years across, much larger moving so quickly, their light waves are stretched objects. than most previous estimates. His model also out. This shifts their energy signals – as we detect But today’s , and the stars they see, held that the Solar System is far from the gal­ them – toward the red end of the electromagnetic will only take Hubble so far. To measure even axy’s center and that all nebulae, including spi­

spectrum, a phenomenon known as “.” greater distances, will need a larger ral nebulae, are within the confines of the Milky The team noticed that dimmer, more distant ob­ telescope and new types of standard candles. Way. Citing photographic surveys done at the jects have a larger redshift than objects closer to One new instrument may hold the key. Last Lick Observatory, Curtis put forth his idea that Earth. As reported in a recent paper, Hubble’s year the Rockefeller Foundation agreed to pro­ spiral nebulae were “island universes,” distant measurements led him to a useful velocity-dis­ vide the six million dollars needed to fund the systems similar to the Milky Way and not tance relationship: increase in direct construction of a new observatory with a 200­ outlying components of it. He also believed the proportion to their distance from us. inch telescope. When completed, this telescope Milky Way was less than 30,000 light years in Hubble’s initial analysis reveals that for ev­ will hold four times the light-gathering power of diameter and 8,000 light years in thickness. ery million parsecs of distance, the velocity of the instrument Hubble currently uses. Hubble’s recent observations vindicate Cur­ the spiral nebulae increases by approximately tis’ views. While bright, diffuse nebulae are at 300 miles per second, where one parsec is equal Einstein’s General Theory Holds True relatively close distances and part of the Milky to 3.26 light years. He determined distances to Way, spiral nebulae are separate systems at great the nebulae using Cepheid variables, stars with The past decade has been an exciting and distances from it. He estimates that the spiral An­ challenging time in the development of scien­ dromeda Nebula is as large and holds as much tific understanding of the universe, with theo­ matter as the Milky Way. However, Hubble’s rists testing their ideas against the framework of findings also support Shapley’s general view of ’s 1916 theory of general relativ­ the Milky Way’s size, with the Solar System lo­ ity. The theory establishes the universe as three cated far from its center. Courtesy of the Carnegie Institution dimensions of space and one of time. It proposes Shapley’s work had increased the size of the Dr. found that the Andromeda nebula is the most distant object known and is not part of the Milky that curves the fabric of space-time and universe by about ten times, but Hubble’s recent Way Galaxy. that the curvature controls the natural discoveries have multiplied it by at least another ten. Shapley observed a historical progression, of bodies in space. Edwin Powell Hubble, of the directly related to their average brightness: the from belief in a small universe with man at its His theory also pointed to the expansion of the of the Carnegie longer the period, the brighter the star. The Small center, to a larger one with Earth further from universe, but Dr. Einstein has rejected the idea. Institution at Pasadena, California, has solved Magellanic Cloud (SMC) is a massive aggregate the center: “The significance of man and the the mystery of the spiral nebulae, the great of stars visible in the southern hemisphere, and In 1917 he added a new term to his equations, Earth…has dwindled with advancing knowl­

heavenly objects that appear as hazy pin-wheels since all of these stars were in the SMC, they Hubble’s research led to this diagram, showing the gen- the “,” designed specifi­ edge of the physical world…” in the sky. He has determined that these objects were at roughly the same distance from the eral correlation between how far away a galaxy is and cally to avoid the implication of an expanding are much more distant than previously thought Earth. Each Cepheid’s intrinsic brightness was the speed it is moving away from us. universe. Hubble’s recent observations dismiss and therefore are themselves, rather directly related to its period. the need for such a term, but while Einstein has than part of our own Milky Way Galaxy. In the Soon after Miss Leavitt’s discovery, Shapley a known , or “standard candles.” He examined the data and believes Hubble’s paper process, Dr. Hubble was also able to determine began systematically searching for Cepheids in concluded that the most distant objects are speed­ to be sound, he is still not convinced. the distance to the spiral Andromeda nebula. globular clusters in the Milky Way galaxy, globes ing away from us at perhaps thousands of miles In 1922, Soviet physicist Alexander Fried­ Classifying Nebulae Hubble’s observations vindicate the views of tens of thousands of densely-packed stars. per second. man developed his own solutions to the general of Dr. Heber Curtis expressed in the “Great He used the period-luminosity relationship to For over a thousand years, astronomers Hubble’s recent discoveries reveal that the relativity equations. He described two possibili­ have speculated on the nature and evolution Debate” with Dr. Harlow Shapley at the 1920 determine the distance to more than 230 globular volume of space itself is expanding. Spiral nebu­ ties for the universe: either it was expanding or of nebulae, faint clouds of gas and dust in the National Academy of Sciences (see “‘Great clusters. On the assumption that Cepheids in lae appear to be moving away from each other at contracting, but it was not static. distant universe. However, until recently, there Debate’ Resolved” article). Curtis maintained distant globular clusters obey the same a rate that increases with distance, but these neb­ Abbe George Lemaître, a Belgian-born have been insufficient observations to allow a that bright diffuse nebulae are relatively close to as nearby Cepheids, he found that the most ulae aren’t just moving. They are being pulled Catholic priest and astronomer, released a paper classification of nebulae based on their features Earth and are part of the Milky Way, while spiral distant clusters reside some 200,000 light years along as the fabric of space-time expands. in 1927 stating that a homogeneous universe of or qualities. nebulae are at great distances and not part of the away. Dr. Hubble, during his studies of the spiral Milky Way. By studying the periods of the Cepheids in Hubble’s findings build on the work of Dr. Ves­ constant mass has to be expanding to account nebulae, proposed a system to classify all On December 30, 1924, Hubble announced the Andromeda Nebula (M31), Hubble was to M. Slipher of in Flagstaff, for the of spiral nebulae. He de­ nebulae, both inside and outside the Milky that he had taken photographic plates of a few able to determine each variable’s intrinsic Arizona, who in 1912 became the first to record scribed a possible universe that was expanding Way. He sorted them into three basic categories: bright spiral nebulae with Mount Wilson’s brightness, its absolute . He then made the electromagnetic spectra of a spiral nebula. Of from its initial state as a single point. Lemaître elliptical, spiral, and irregular. These, in turn, Hooker telescope, the largest observations of the apparent magnitude of every the more than forty spectra Slipher subsequently believed that before this expansion began, the were further subdivided according to shape in the world. According to Hubble, “The 100­ one. Once he knew the difference between how gathered, all but a few were measurably redshift­ universe did not exist. (spherical to elongated ellipses, for example) inch reflector partially resolved a few of the bright a star appeared and how bright it actually ed, and therefore are moving away from us. His Hubble’s discoveries answer many ques­ and structure (hazy to distinct spiral arms, barred nearest, neighboring nebulae into swarms of was, he was able to calculate its distance from studies, however, led him to a conclusion that ve­ tions, but they also present a new direction for spirals, etc.). stars.” the Earth. He found Andromeda to be 900,000 locities for the nebulae might be closer to a mere the future of cosmological studies. Hubble’s schema shows a sequence of Hubble estimates the Andromeda Nebula is light years away – the most distant object known 600 miles per second. evolutionary change but was “based primarily on as large, and holds as much matter as the Milky to date. the structural forms of photographic classification Way. It may contain some three to four thousand which should be entirely independent of million stars that produce one billion times the theoretical considerations.” Future astronomical light of the . The Minds Atop Mount Wilson studies and evidence will be the test for this new images revealed not only classification system. individual stars within the nebulae, but that some High above Pasadena, California in the The next year, Hubble returned to the Uni- When the telescope was completed in 1917, of the stars changed in brightness over time. , the astronomers at the versity of for a PhD, researching faint Mr. Humason was hired as a janitor and electri­ Known as stars, these stars were Carnegie Institution’s Mount Wilson Observa­ nebulae at the . However, US cian. His intelligence and curiosity were soon no- the key to determining distances to the nebulae. tory are changing our view of the Universe. entry into the Great War led him to rush through ticed, and it wasn’t long before he was promoted The intrinsic luminosity, or actual brightness, of Who are these scientists? his dissertation and oral exam; he reported to the to night assistant on the 60-inch telescope. the Cepheids in the nebulae Hubble studied was army three days later. Hubble served in France Working under the observatory’s director, Dr. known. Since the same star will appear dimmer Athlete-Scholar Unveils the Future of until the end of the war, when he returned to ci- , Humason became an ex­ the more distant it is, the apparent magnitude of the Universe vilian life to take up a position that had been pert observer. Dr. Hale recognized his abilities these stars is a clear indicator of the distance to offered two years earlier – at the Mount Wilson and appointed him to the observatory’s scientific their host nebulae. Born in Marshfield, , in 1889, Ed­ Observatory. staff in 1919. Humason soon became an expert Hubble’s work builds upon earlier win Powell Hubble’s early life centered on at measuring the redshifts of distant nebulae and observations by Miss athletics, primarily track and field events. At 6 Former Mule-Team Driver and Janitor the chief assistant and collaborator to Dr. Hub- of the Harvard College Observatory and by foot 3 inches in height, he was quite successful, Helps Discover Expanding Universe ble. Shapley of the Mount Wilson Observatory. even setting an Illinois state record for the high In 1912, Miss Leavitt was the first to recognize jump. Milton Lasalle Humason was born in Dodge the importance of Cepheid variables. They are At the , he focused Center, Minnesota in 1891, but moved to Cal­ In Their Own Words giant stars, often visible from great distances, on and , but his studies ifornia with his family as a child. Having left and each varies in brightness over time. took a different direction when he attended Ox­ school in the eighth grade, Humason received “New observations by Hubble…make it appear likely beyond the last frontier, now 140,000,000 light years Cepheids are named after the first such star of ford University as a Rhodes Scholar. There he no formal training as an astronomer. In fact, his that the general structure of the Universe is not static.” away. We, or our successors, may actually know famil­ its type found: Delta Cephei in the constellation studied Roman law and Spanish but still made career at Mount Wilson began as a mule-team – Albert Einstein – 1925 iarly the farthest borders of this vast Universe and learn Cepheus. While counting their number, as facts about it so astounding that astronomers of today the time to compete in water polo and field driver for the pack trains that carried large com­ captured on photographic plates of the small “Tomorrow the outlook may change and new methods would be nearly unable to comprehend their signifi­ events. He returned to the US in 1913 to teach ponents of the telescope and its building to the cloud of Magellan, Miss Leavitt noticed that may dwarf our knowledge and beliefs of today, or con- cance.” – Edwin Hubble – 1927 high school physics and Spanish. top of Mount Wilson during the observatory’s the Cepheids had periods, or repeating cycles, vert them into remote history. Soon we may look far construction.

www..gov For Lessons & Teacher Guide, see http://cosmictimes.gsfc.nasa.gov/ NW-2009-5-072-GSFC (2 of 6)