National Aeronautics and Space Administration Age of the Universe: Size of the Universe: 2 Billion Years Cosmic Times 280 Million Light Years 1929 Andromeda Nebula Lies Universe is Expanding “Great Debate” Resolved Dr. Hubble’s discovery settles the “Great “Red Shift” is Proof of Einstein’s General Theory Debate” over the size of our own Milky Way Galaxy and the distance to, and nature of, spiral Outside Milky Way Galaxy Using the 100-inch Hooker Telescope at Although Hubble’s work presents a tremen­ nebulae. Mount Wilson Observatory, Dr. Edwin Powell dous breakthrough in our understanding of the Held on April 26, 1920 at the National Acad­ Spiral Nebulae are indeed “Island Universes” Hubble has studied a variety of spiral nebulae universe, one big question remains. How far out emy of Sciences 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. Harlow Shapley 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 motion 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 stars, 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 telescopes, 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 “redshift.” greater distances, astronomers 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 star systems similar to the Milky Way and not tance relationship: redshifts 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 Albert Einstein’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. Edwin Hubble found that the Andromeda nebula is the most distant object known and is not part of the Milky that gravity curves the fabric of space-time and universe by about ten times, but Hubble’s recent Way Galaxy. that the curvature controls the natural motions discoveries have multiplied it by at least another ten. Shapley observed a historical progression, of bodies in space. Astronomer 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 Mount Wilson Observatory 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 “cosmological constant,” 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 galaxies 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 luminosity, 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 physics 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 Lowell Observatory in Flagstaff, for the radial velocity 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 magnitude. 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 reflecting telescope 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.