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Home Edition Age of the Universe: Cosmic Times Size of the Universe: 2 Billion Years 1929 280 Million Light Years Andromeda Nebula lies outside the Milky Way Galaxy Spiral Nebulae are indeed “Island Universes”

stronomer Edwin Hubble, inch reflector partially resolved a of the Mount Wilson few of the nearest, neighboring AObservatory at Pasadena, [spiral] nebulae into swarms of California, has solved the mystery stars.” One of the nearby nebulae of the spiral nebulae. The spiral Dr. Hubble photographed was the nebulae look like hazy pin-wheels Andromeda Nebula. He estimates in the sky. He has determined it is as large as the Milky Way that these objects are much more and holds as much matter. It may distant than previously thought. contain some three to four billion Therefore, they are distant galaxies stars that produce one-billion times and not part of our own Milky Way the light of the Sun. galaxy. In the process, Dr. Hubble was also able to determine the These photographs showed there distance to the spiral Andromeda were individual stars in the nebula. Nebula. They also showed some of the stars changed in brightness over Dr. Hubble’s observations support time. Known as Cepheid variable Image credit: Hale Observatories, courtesy AIP Emilio Segre Visual Archives the views Dr. Heber Curtis stars, these stars were the key Edwin Hubble at Mount Wilson Obser- expressed in a debate with Dr. to determining distances to the vatory Harlow Shapley in 1920. Curtis nebulae. The true brightness of stated that bright diffuse nebulae the Cepheids in the nebulae Swan Leavitt of the Harvard College are fairly close to Earth and are Hubble studied was known from Observatory and by Dr. Harlow part of the Milky Way, while spiral how the Cepheid changes its Shapley of the Mount Wilson nebulae are at great distances and brightness. Scientists had already Observatory. not part of the Milky Way. known exactly how light dims over distance. The distance to the star, In 1912, Miss Leavitt was the On December 30, 1924, Hubble and the nebula it is located in, first to recognize the importance announced that he had taken can be found by comparing the of Cepheid variables. They are photographs of a few bright spiral apparent brightness of these stars giant stars, and each varies in nebulae with the Mount Wilson to their true brightness. brightness over time. Cepheids Hooker telescope, the largest are named after the first such star reflecting telescope in the world. Dr. Hubble’s work builds on earlier of its type found: Delta Cephei in According to Dr. Hubble, “The 100 observations by Miss Henrietta “Andromeda” continued on page 2 “Andromeda” continued from page 1 2 Classifying Nebulae the constellation Cepheus. While further subdivided according to studying Cepheids in the Small or over a thousand years, astronomers wondered about shape (spherical to elongated Magellanic Cloud, Miss Leavitt the nature and development ellipses, for example) and structure noticed that the Cepheids would F of nebulae. Nebulae appear to be (hazy to distinct spiral arms, barred brighten, then fade, and then faint clouds of gas and dust in the spirals, etc.). brighten again. The length of time distant universe. Until recently, there it took for the star to go through have not been enough observations Hubble’s system shows a sequence this cycle (the period) was directly to classify nebulae based on their of evolutionary change but was related to its true brightness: the features or qualities. “based primarily on the structural longer the period, the brighter the forms of photographic classification star. The Small Magellanic Cloud During his studies of the spiral which should be entirely independent is a large group of stars visible in nebulae, Dr. Hubble proposed of theoretical considerations”. the southern hemisphere. Since a system to classify all nebulae. Future astronomical studies and all of these stars were in the Small He sorted them into three basic evidence will be the test for this new Magellanic Cloud, they were at categories: elliptical, spiral, and classification system. ♦ irregular. These categories were roughly the same distance from the Earth. Each Cepheid’s true

brightness was directly related to NASA its period. Elliptical Galaxies Spiral Galaxies Barred Spiral Galaxies Soon after Miss Leavitt’s discovery, Images From & STScI Dr. Shapley began searching for “Great Debate” Resolved Cepheids in globular clusters in our own Milky Way galaxy. Globular r. Hubble’s discovery settles Milky Way was less than 30,000 clusters are sphere-shaped the “Great Debate” over the light years in diameter and 8,000 groups of tens of thousands of size of our own Milky Way light years in thickness. densely packed stars. He used D galaxy. It also settles the question the period-brightness relationship of the distance to spiral nebulae Dr. Hubble’s recent observations to determine the distance to more and what they are. support Curtis’ views. While bright, than 230 globular clusters. He diffuse nebulae are relatively close assumed that Cepheids in distant Held on April 26, 1920 at the and part of the Milky Way, spiral globular clusters act the same as National Academy of Sciences nebulae are separate systems nearby Cepheids. Based on that in Washington, D.C., the debate located far away from it. He assumption, he found the most focused on the opposing views of estimates the spiral Andromeda distant clusters in the Milky Way astronomers Harlow Shapley and Nebula is as large and holds as Galaxy are about 200,000 light Heber D. Curtis. much matter as the Milky Way. years away. However, Hubble’s findings also Shapley’s studies led him to describe support Shapley’s ideas about the By studying the periods of the the Milky Way as an enormous Milky Way’s size and the location of Cepheids in the Andromeda galaxy of stars some 300,000 light the solar system. Nebula, Dr. Hubble was able to years across. This is much larger determine the true brightness (or than most previous estimates. He Shapley’s work had increased also said the solar system is far the size of the Universe by about absolute magnitude) of each. He from the galaxy’s center and that all ten times, but Hubble’s recent then made observations of their nebulae, including spiral nebulae, discoveries have multiplied it apparent brightness (or apparent are located within the Milky Way. by at least another ten. Shapley magnitude). Once he knew the observed a historical progression, difference between how bright a Using photographs he had taken from belief in a small universe star appeared and how bright it as evidence, Dr. Curtis presented with man at its center, to a larger truly was, he was able to calculate his idea that spiral nebulae were one with Earth further from the its distance from the Earth. He “island universes,” or distant star center: “The significance of man found Andromeda to be 900,000 systems similar to the Milky Way. and the Earth…has dwindled light years away – the most distant They were not a part of the Milky with advancing knowledge of the object known to-date. ♦ Way galaxy. He also believed the physical world…” ♦ 3 The Universe is Expanding

“Red Shift” is Proof of Einstein’s General Theory

sing the 100-inch Hooker Telescope at Mount Wilson UObservatory, Dr. Edwin Hubble has studied many spiral nebulae. He has discovered they are moving away from us at a rapid pace. This is strong evidence of an expanding universe. He has further determined that the farther the Image Credit: Hubble, PNAS, 15, 3 (1929) nebula, the faster it moves away. Hubble’s diagram showing the relationship between galaxy distance and velocity

Hubble and colleague Milton Hubble’s findings build on the work with a 200-inch telescope. This Humason measured the speeds of Dr. Vesto M. Slipher of Lowell new telescope will collect four and distances for twenty-four of Observatory in Flagstaff, AZ. In times more light than the 100 inch these nebulae. Because they 1912, Dr. Slipher first recorded the telescope Hubble currently uses. are moving so quickly, their light electromagnetic spectra of spiral waves (electromagnetic spectra) nebulae. All but a few of the forty are stretched out. Because red Einstein’s General Theory spectra Slipher later gathered were light has the longest wavelength, very red-shifted. This means almost Holds True this phenomenon is known as all of them were moving away from “redshift.” The team noticed that us. However, his studies lead him The past decade has been an dimmer, more distant objects have to a conclusion that speeds for the exciting and challenging time a larger redshift than objects closer nebulae might be closer to only 600 in the development of scientific to Earth. As reported in a recent miles per second. understanding of the Universe. paper, Hubble’s measurements During this time scientists have led him to a useful speed-distance Although Hubble’s work presents been testing their ideas about the relationship: redshifts increase in a big breakthrough in our Universe against Einstein’s 1916 direct proportion to their distance understanding of the Universe, one Theory of General Relativity. The from us. big question remains; how far out theory describes the universe as into the Universe does his model three dimensions of space (length, Dr. Hubble determined distances hold? The 100-inch telescope can width, and depth) and one of time. It to the twenty-four nebula using clearly show Cepheids in only the says that gravity curves this space­ Cepheid variable stars. These nearest nebulae. In very distant time and that the curvature controls are stars that astronomers use nebulae, where Cepheids are the natural motions of objects in to determine the distance to the barely visible, Hubble uses the space. nebulae they are found in. Once brightest individual stars, some he knew how far away the nebulae 50 to 100 times brighter than the Einstein’s theory also suggested were, he could compare their Cepheids, as standard candles. the expansion of the Universe, but distance to their red-shift to learn Einstein didn’t believe this could be the relationship. He concluded Today’s telescopes, and the stars correct. In 1917 he added a new term that the most distant objects are they see, will only take Dr. Hubble to his equations, the “cosmological speeding away from us at perhaps so far. To measure even greater constant.” This constant was thousands of miles per second. distances, astronomers will need a designed to avoid the possibility of larger telescope and new types of an expanding universe. Hubble’s Dr. Hubble’s recent discoveries standard candles. recent observations remove the show that the volume of space need for this term. While Einstein itself is expanding. Spiral nebulae One new instrument may hold has examined the data and believes appear to be moving away from the key. Last year the Rockefeller Dr. Hubble’s paper to be sound, he each other at a rate that increases Foundation agreed to provide is still not convinced the universe is with distance, but these nebulae six million dollars to fund the expanding. aren’t just moving. They are being construction of a new observatory pulled along as space expands. “Universe Expanding” continued on page 4 4 The Minds atop Mount Wilson

igh above Pasadena, events. He returned to the US in son received no formal training as California in the San Gabriel 1913 to teach high school physics an astronomer. In fact, his career HMountains, the astronomers and Spanish. at Mount Wilson began as a mule- at the Carnegie Institution’s Mount team driver for the pack trains that Wilson Observatory are changing The next year, Hubble returned to carried large parts of the telescope our view of the Universe. Who are the University of Chicago to earn and its building to the top of Mount these scientists? his PhD and began researching Wilson during the observatory’s faint nebulae at the Yerkes Obser­ construction. Athlete-Scholar Unveils the vatory. However, his research was Future of the Universe interrupted when the US entered When the telescope was complet­ the Great War, and he quickly ed 1917, Mr. Humason was hired as Born in Marshfield, Missouri in joined the army. Hubble served a janitor and electrician. His intelli­ 1889, Edwin Powell Hubble’s early in France until the end of the war. gence and curiosity were soon no­ life centered on athletics, primar­ Then he returned to civilian life to ticed, and it wasn’t long before he ily track and field events. At 6 foot take up a position that had been of­ was promoted to night assistant on 3 inches in height, he was quite fered to him two years earlier at the the 60-inch telescope. successful, even setting an Illinois Mount Wilson Observatory. state record for the high jump. Working under the observatory’s Former Mule-Team Driver director, Dr. George Ellery Hale, At the University of Chicago, he and Janitor Helps Discover Humason became an expert ob­ server. Dr. Hale recognized his abil­ focused on mathematics and as­ Expanding Universe tronomy. His studies took a dif­ ities and appointed him to the ob­ ferent direction when he attended servatory’s scientific staff in 1919. Milton Lasalle Humason was born Humason soon became an expert Oxford University as a Rhodes in Dodge Center, Minnesota in Scholar. There he studied Roman at measuring the redshifts of dis­ 1891, but moved to California with tant nebulae and the chief assistant law and Spanish but still made time his family as a child. Having left and co-worker with Dr. Hubble. ♦ to compete in water polo and field school in the eighth grade, Huma­

“Universe Expanding” continued from page 3 In Their Own Words

In 1922, Soviet scientist Alexander Friedman developed his own omorrow the outlook may change and new solutions to the general relativity methods may dwarf our knowledge and beliefs equations. He described two Tof today, or convert them into remote history. possibilities for the Universe: either Soon we may look far beyond the last frontier, now it was expanding or contracting, but 140,000,000 light years away. We, or our successors, it was not staying the same. may actually know familiarly the farthest borders of this vast Universe and learn facts about it so astounding Abbé George Lemaître, a Catholic that astronomers of today would be nearly unable to priest and astronomer released

Image credit: Hale Observatories, courtesy AIP Emilio Segre Visual Archives comprehend their significance. a paper in 1927. This paper said a homogeneous universe --Edwin Hubble, 1927 of constant mass has to be expanding to account for the speed of spiral nebulae moving away. He described a possible universe that was expanding from an initial single point. Lemaître believed that before ew observations by Hubble… make it appear this expansion began, the Universe likely that the general structure of the Universe did not exist. Nis not static. Hubble’s discoveries answer many --Albert Einstein, 1925 questions, but they also present a new direction for the future studies credit: Image Ferdinand Schmutzer, via Wikimedia Commons of the Universe. ♦