Allan Rex Sandage died of pancreatic cancer at his home in San Gabriel, California, in the shadow of Mount Wilson, on November 13, 2010. Born in Iowa City, Iowa, on June 18, 1926, he was 84 years old at his death, leaving his wife, former astronomer Mary Connelly Sandage, and two sons, David and John. He also left a legacy to the world of astronomical knowledge that has long been universally admired and appreciated, making his name synonymous with late 20th-Century observational cosmology.The only child of Charles Harold Sandage, a professor of advertising who helped establish that academic specialty after obtaining a PhD in business administration, and Dorothy Briggs Sandage, whose father was president of Graceland College in Iowa, Allan Sandage grew up in a thoroughly intellectual, university oriented atmosphere but also a peripatetic one taking him to Philadelphia and later to Illinois as his father rose in his career. During his 2 years in Philadelphia, at about age eleven, Allan developed a curiosity about astronomy stimulated by a friend's interest. His father bought him a telescope and he used it to systematically record sunspots, and later attempted to make a larger 6-inch reflector, a project left uncompleted. As a teenager Allan read widely, especially astronomy books of all kinds, recalling in particular The Glass Giant of Palomar as well as popular works by Eddington and Hubble (The Realm of the Nebulae) in the early 1940s. Although his family was Mormon, of the Reorganized Church, he was not practicing, though he later sporadically attended a Methodist church in Oxford, Iowa during his college years. Sandage knew by his high school years that he would engage in some form of intellectual life related to astronomy. He particularly recalls an influential science teacher at Miami University in Oxford, Ohio named Ray Edwards, who inspired him to think critically and "not settle for any hand-waving of any kind." [Interview of Allan Rex Sandage by Spencer Weart on 22 May 1978, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD, USA, www.aip.org/history/ohilist/ and http://www.aip.org/history/ohilist/4380_1.html] Allan enrolled in Miami University in 1943 because his father was on the faculty there at the time. He majored in physics until he entered the Navy for 18 months to train as an electronics technician's mate. His training began in Chicago, where he became acquainted with others interested in astronomy, like Arthur Code and Albert Wilson, and then his tour took him to Gulfport, Mississippi, and finally to Treasure Island in the San Francisco Bay. When Sandage was discharged from the Navy his father was moving to the University of Illinois, so Allan transferred there, entering a much larger and more competitive physics department. He majored in physics and mathematics but he also minored in philosophy, and took a celestial mechanics course from Robert H. Baker. He volunteered to work at the observatory, learning the art and craft of calibrating photographic plates so that magnitudes could be transferred and intercompared from plate to plate, an experience that he later realized prepared him well for his life career and also introduced him into Bart Bok's "star counting" circuit based at Harvard. In consequence, when Bok visited Illinois sometime in 1947, he invited Sandage to work at Harvard in their summer school at the Agassiz Station mapping Milky Way fields. Sandage applied both to Harvard and Caltech for graduate school. Harvard was very well established in its graduate program whereas Caltech was just beginning to offer the Ph.D. in astronomy. He chose Caltech because that was where the big telescopes were. His family had visited Mount Wilson in 1941 during a summer when his father was teaching at Berkeley, and since that time Sandage had dreamed of observing with those giant telescopes. Thus in September 1948, Sandage joined the first class of students to engage in formal graduate work at Caltech under the direction of Jesse Greenstein, who had been recruited from Yerkes for the purpose of establishing a Ph.D. program. Together with Halton C. Arp, Helmut Abt, and Morton Roberts, Sandage learned stellar atmospheres, interiors and the interstellar medium under Greenstein, along with relativity from H. P. Robertson and quantum mechanics from Richard Feynman. His first research paper, guided by Greenstein, utilized equivalent width data by R. B. King at Mount Wilson to explore the effect of temperature stratification in the solar atmosphere. It did not take long before Sandage found a path to the big telescopes. Edwin Hubble had approached Greenstein to recommend a student who might provide assistance determining the distribution of galaxies in deep space with plates then being taken with the newly opened 48-inch Schmidt at Palomar. As Ira Bowen reported in his 1949 director's report, Hubble, "with the assistance of A.R. Sandage, is studying on some of these plates the distribution of faint nebulae in standard apparently normal regions of the sky." [Bowen, PASP 61 (1949), 250.] In the first year, Sandage's efforts were limited to processing Hubble's plates at Santa Barbara Street, but when Hubble suffered a massive heart attack on vacation in 1951, Sandage took over securing the fields with the Schmidt, trained carefully by Milton Humason. Upon Hubble's death in 1953, Sandage assumed the mantle. As Sandage searched for a thesis topic in 1951, Hubble had no specific problems at hand that were appropriate, so Walter Baade agreed to take him on. Baade had trained both Sandage and Arp on securing photometric data on globular clusters with the Mount Wilson 60-inch, and now, teamed with William Baum, who was adept in the new photoelectric photometry, the three began pushing deeper to reach the main sequences of globular clusters, something no one had yet seen. M92 was their first target, and then Sandage took on M3 for his thesis. Together these efforts revealed the main-sequence turnoffs for the first time, and within a short time, in collaboration with Martin Schwarzschild at Princeton, they began to realize that cluster ages were on the order of at least 3 billion years, which agreed far better with geological time estimates for the earth's age than did Hubble's expansion value of 1.8 billion. This was also the beginning of the realization that red giants were evolved main-sequence stars, which was to become a hallmark of team work in modern astronomy at the observational-theoretical interface, centered around young astronomers like Sandage who were nurtured by Schwarzschild and Baade. Throughout the 1950s Sandage worked along two major lines: revising and refining the Hubble Constant and clarifying the observational evidence for relative cluster ages, adding open clusters to create a powerful composite portrait of the migration of turn-off points down the HR diagram with advancing cluster age. These composite cluster diagrams provided new physical insights into the evolution of luminosity functions and many of the quirky characteristics of color magnitude diagrams. In collaboration with Olin Eggen and Donald Lynden-Bell, in the late 1950s through the early 1960s Sandage also formulated a collapse scenario for the evolution of the Milky Way, in a defining paper that has thus far garnered over 1400 citations. This was an important factor to consider in meeting his primary goal, to extend the Hubble diagram deep enough into space and time to be able to discriminate between various contending models for the history of the universe: its overall geometry and whether the expansion was constant, speeding up, or slowing down. Any evolutionary scenario for galaxies themselves would alter their observed characteristics, and hence influence one of the many distance indicators that had been devised by Hubble and those following him. Thus his efforts at establishing the Hubble Constant in following years included a staunch defense of a particular evolutionary scenario for galaxies that envisioned no observable changes in luminosity criteria. Others, notably Beatrice Tinsley, showed that colors and luminosities did change appreciably, which significantly changed the distance scale. Sandage held to his particular way of recalibrating and refining the many elements of the cosmic distance ladder, however, and his influence led, as Albert Whitford ruefully observed in 1978, to an impasse for those who, following Tinsley, realized that "the evolutionary corrections almost certainly have to be on the side that would reverse Sandage's conclusions." [Interview of Albert G. Whitford by David DeVorkin on 17 July 1978, AIP. http://www.aip.org/history/ohilist/5147_1.html/] Over the years, Sandage made many downward revisions of Hubble's value, prompted by a succession of recalibrations and reclassifications employing all the powers of the 200-inch Hale reflector. His first recalibration, with Milton Humason and N. U. Mayall in 1956, based on the realization that objects Hubble thought were very bright stars were actually huge H II regions, reduced the Hubble Constant from 530 to 180 km/sec/Mpc, thereby increasing the age of the universe by an inverse factor. This massive report, which increased the number of galaxies in the sample from the low 100s to over 800, garnered about one thousand citations to date and was just the first of a series of adjustments that eventually brought the Constant to 55 km/sec/Mpc in 1975, combining evidence from bright spirals, the Virgo Cluster, and from remote Sc I galaxies. They concluded forcefully that the "local velocity field ... is as regular, linear and isotropic as one can measure it." Sandage defended this conclusion and his low range for the Constant for the rest of his life. The standoff was stifling, as Bart Bok commented in 1977, "H is unbelievably bad now. We have Sandage's H of 50, against van den Berg's H of 90. Now, the difference between 50 and 90 is almost a factor of two, which is a factor of eight in the volume and hence a factor of eight uncertainty in the densities in intergalactic space." [Interview of Bart Bok by David DeVorkin circa June 1978, AIP. www.aip.org/history/ohilist/] In 1961, Sandage's magisterial homage to his exemplar, The Hubble Atlas of Galaxies, became state of the art in the minds and hearts of young astronomers. "I have acted mainly as an editor," he claimed in his preface, "of a set of ideas and conclusions that were implicit" in Hubble's own unpublished notes, from the mind of the master. Intent upon finishing what Hubble had set out to do, Sandage ultimately surpassed him. With Gustav A. Tammann in 1981, he released a new reclassification and published it as the Revised Shapley-Ames Catalog, an achievement that Vera Rubin hailed as an "unsurpassed ... source of consistent morphological types for bright galaxies." [Vera Rubin, Bright Galaxies, Dark Matters, AIP, 1997, p. 90] In 1985, Sandage, with Tammann and R. Cadonau, reported that supernovae of Type 1A could be reliable indicators of distance over extragalactic scales, a new rung in the distance ladder that has proven to be immensely useful in recent decades. Sandage was also the first to isolate the optical spectrum of an enigmatic radio star, one of many sources in the Cambridge radio surveys now known as quasars that defied confirmation in the visible spectrum. He was not able to untangle the odd spectrum although he showed that its light intensity varied over relatively short time scales. Sandage symbolized the epitome of the classic optical astronomer. He relished long and frequent nights at the telescope, facing the heavens and its mysteries head on, once remarking that it was only in situ observing that provided the isolation and concentration that put his mind "in a state when its more receptive to call things up from its deep recesses." [Quoted in Kelly Beatty "Tribute to a Pioneering Cosmologist," S&T website November 15, 2010, SkyandTelescope.com - Homepage News - Tribute to a Pioneering Cosmologist.mht] Sandage deeply believed that true "knowledge . . . came directly from the sky rather than by dialectic discussion or revelation." [Allan Sandage, "Edwin Hubble 1889-1953" JRASC 83 #6 (December 1989)] With convictions like these it is not surprising that cross-over physicists who engaged him, such as Edwin Salpeter, expressed amazement that Sandage could command resources available to no other astronomer, or that he could sit on invaluable catalogue data for years before releasing it as a whole argument. [Interview of Edwin Salpeter by Spencer Weart, 30 March 1978, AIP. http://www.aip.org/history/ohilist/4854.html/] Colleagues, writers and historians who encountered him during his mature years consistently remarked on his competitiveness and fierce defense of his results. At the end of a long and passionate essay on Edwin Hubble in 1989, Sandage coyly remarked on the present state of the Hubble Constant, "But it must be fairly pointed out that some astronomers, not believing the problem of the distance scale has been solved by the results of the 200-inch programme from 1950 to 1980, have suggested that the value of the Hubble constant can be determined to the satisfaction of the skeptics only by the future use of the Hubble Space Telescope. For this one suspects that Hubble might have been pleased." [Allan Sandage, "Edwin Hubble 1889-1953" JRASC 83 #6 (December 1989)] Though not formally religious early on, Sandage became deeply spiritual in his outlook on life and the universe, and on the practice of astronomy. As Donald Lynden-Bell commented in an online Guardian obituary, "Sandage believed that he was discovering the age of creation ..." [9 December 2010, "Allan Sandage Obituary" guardian.co.uk] And in a 2002 essay for the "Truth Journal," Sandage revealed that he believed that astronomical discovery had theological significance. He took as an example the Big Bang, was it akin to the search for first cause? In answer, Sandage asserted that "Astronomers may have found the first effect, but not, thereby, necessarily the first cause sought by Anselm and Aquinas." Ultimately, Sandage resorted to Design: "I am convinced that the existence of life with all its order in each of its organisms is simply too well put together."[Allan Sandage, "A Scientist Reflects on Religious Belief," Truth Journal, Leadership U. c1995-2011, updated 14 July 2002] Sandage spent his entire career at Mount Wilson-Palomar. It "was like entering Valhalla" Sandage recalled in his 1978 interview with Spencer Weart, from which many of the quotations here are derived. Accordingly he "put pressure on myself, to live up to that responsibility." The chief responsibility was to use the telescope to its utmost, and for that dedication, astronomy will forever be in his debt. Every prize and honor normally bestowed on astronomers came to Sandage during his lifetime. In 2000, he won the first Peter Gruber Cosmology Prize, sharing the honor with James Peebles. Revealing his deep regard for the history of his chosen subject, Sandage donated the prize to the American Institute of Physics Center for History of Physics. He soon followed that by an even bigger gift, his production of the Centennial History of the Carnegie Institution of Washington: Volume 1, The Mount Wilson Observatory: Breaking the Code of Cosmic Evolution (Cambridge University Press, 2005). For that, historians of astronomy will forever be in his debt. Given his great influence, and his central and at times controversial role during a period when the study of cosmology went through profound change, mainly in the breadth of the tools that can be brought to bear on the deepest of questions, Sandage warrants closest attention by the best and most persistent historians of science and human values. He has already been the subject of contemporary writers, appearing as a character of considerable complexity in works by colleagues, associates, and competitors. At this writing, placement of his personal papers has not yet been announced. Vera Rubin, Owen Gingerich, Spencer Weart, and the editors have provided helpful guidance in the preparation of this notice.