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Allan Sandage, surveyor of the cosmos, dies at 84

sandage2[1].jpgA spokeswoman at Carnegie Institution for Science (CIS) in Pasadena, California, has confirmed to Nature that Allan Sandage, an influential US astronomer who once worked as the assistant to Edwin Hubble, has passed away. He was 84. No further details on Sandage’s death were available from CIS press office, which is now preparing an obituary press release.

From the time of his work with Hubble to his later investigations using data from the Hubble Space Telescope (HST), Sandage’s career spanned the decades between astronomers’ first precise measurements of the distances to remote galaxies to the modern discovery that a mysterious dark energy is driving them apart from one another. He played a key role in the initial discovery of quasars and produced a definitive photographic atlas of galaxies.

Sandage was well known for his precision observations of Cepheid variable stars, which he used to determine the age and expansion rate of the Universe – the so called Hubble constant. For much of his career he was the leading proponent of an older, larger universe with a relatively low Hubble constant of about 50. Subsequent measurements with the HST have since yielded a figure around 70. (A number of apparent contradictions related to the age of the Universe were resolved after 1998 when it was understood that the expansion of space is accelerating due to dark energy.)

Sandage received his PhD at the California Institute of Technology in 1953 and from 1952 onward was on staff at the celebrated Mount Wilson and Mount Palomar observatories, now part of the Carnegie Institution. Among other honors, he was awarded the US National Medal of Science in 1970, the Bruce Medal (from the Astronomical Society of the Pacific) in 1975 and the Crafoord Prize (from the Royal Swedish Academy of Sciences) in 1991.

Photo courtesy Carnegie Insitution for Science.

Jointly posted with Ivan Semeniuk

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    Gisella Clementini said:

    Allan has always been a very special person to me since I first met him in 1983 at the beginning of my carrier in Astronomy, to our last meeting in January 2005 when I visited him in Pasadena. I would have left astronomy long ago if I had not had a very long chat with him in 1983.

    I can’t believe he is not with us anymore and feel in very deep sorrow.

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    Henry Ferguson said:

    I first met Allan Sandage when I was in graduate school and ended up doing my PhD thesis with him. He was truly inspirational. His knowledge was encyclopedic. He was the kind of person who stood out in a crowd, but not just because of his booming voice and infectious jolly laugh. He could converse on any topic and always have something interesting to contribute. And it always seemed like he would like nothing more than to have that conversation. Many astronomers referred to him as “uncle Allan,” and he often referred to himself that way in later years. In many ways he was the charming, eccentric, curmudgeonly, uncle about whom everyone has an anecdote.

    He was prolific. He had over 200 publications, some of which are the most highly cited in astronomy. His color-magnitude diagram of the globular cluster M3, published in 1953, represented a fundamental advance in our understanding of how stars evolve and was the first serious measurement of the ages of the oldest stars in our galaxy. He pioneered this kind of study of stellar populations, which is a burgeoning field in astronomy even today.

    In his 1961 paper on “The Ability of the 200-inch Telescope to Discriminate Between Selected World Models,” he laid out a roadmap for making observational measurements of the geometry of the universe. This is one of the all-time classic papers in cosmology and set the agenda for work that continues today with the Hubble Space Telescope. Measuring the expansion rate (the Hubble constant) became a major focus of his later research. Much of what he did in this field was pathbreaking and fundamentally sound. He was not shy in pointing out the flaws in work with which he disagreed, which generally resulted in a heated debate that raised everyone’s game (even if it did stray into polemics from time to time). The fact that the most accurate measurements today – made by Adam Riess and collaborators in 2009 – indicate a a higher value than he preferred, should not diminish his contributions to the field.

    He was a galaxy cartographer and taxonomist par excellence. His “Hubble Atlas of Galaxies” became the essential reference for anyone classifying galaxies and studying their structure. His Revised Shapley-Ames catalog was for many years one of the most important resources for studying nearby galaxies and using them as tracers of large-scale structure. He carried out some of the most extensive surveys of nearby clusters of galaxies, using giant photographic plates from the du Pont telescope in Chile.

    His most cited paper is his 1962 work with Eggen and Lynden-Bell — “Evidence from the motions of old stars that the Galaxy collapsed.” This paper was among the first to use the “fossil record” of the motions of old stars in our galaxy to try to infer something fundamental about the way the galaxy formed. While the views on how this collapse took place have evolved over the years, this, like many of his other papers, set the agenda for an entire field of astrophysics.

    I have heard that Allan could be a difficult person. I never really experienced that, although I did receive a few good-natured criticisms when I strayed into working on the Hubble constant later in my career. When I was working on my PhD, he was an amazing mentor. He read every draft of my thesis chapters within a day or two and wrote voluminous comments in the margins. He told me that the most important lesson he learned when he first got to Carnegie was how important it was to write well. Of course I thought I already did write well, but I learned a lot from him about how to express myself more clearly and how to focus on what was most important. I also remember several conversations lasting many hours where we would move stream-of-consciousness from some nitty-gritty aspect of my thesis to grand ideas for using some property of galaxies as a more accurate probe of the geometry of the universe or a more sensitive test that the expansion of the universe is real. For an impressionable graduate student, the idea that one should be thinking about the universe as a whole — even while focusing on some obscure corner of it — was a fundamental lesson in how to do science.

    More than anyone else I have ever met, Allan Sandage lived astronomy. That may be why he took so many aspects of scientific disagreements so personally. Astronomy has lost one of the all-time greats, and many of us have lost our uncle Allan.

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