SHAPLEY’S KEY CONTRiBUTIONS TO SCIENCE
Harlow Shapley mapped our Milky Way galaxy by a ‘ladder’ he devised for measuring vast distances across space (1914-21). Besides a new and correct model of our galaxy, his ladder was used by Edwin Hubble to find galaxies beyond ours - the universe. Besides his revolutionary model of our Galaxy Shapley made other Key Discoveries in a long and restless scientific career. Here are 5 (ants, to white dwarf xs). Here also are three Breakthrough Contributions by which Shapley impacted our thinking, for example, on search for life. Also see his Missed Discoveries. When asked to tell his scientific mistakes, Shapley would say: “You said that lecture was to be one hour!”
Ladder Scaled the Galaxy -
But Shapley built a new ladder for measuring distances never attempted by astronomers. He based his ladder on some very bright Cepheid variable stars that Henrietta Swan Leavitt had just found to change their apparent light periods according to distance: the period-luminosity or p-l Law.
Shapley made the first effective calibration of distance from earth to Leavitt’s Cepheids, which were in the Small Magellanic Cloud (SMC). Thus Shapley measured (and revised) this rung of his distance ladder.
His further work on Cepheids turned them into standard candles. Cepheids became rungs for probing more distant globular clusters. His 3-D map of 69 globular clusters, drawn in Fig 1, outlined a wide flat galaxy with a bulging center and the eccentric location of our Sun.
Fig. 1 Yellow dots are Shapley’s 69 globular clusters as seen across the galaxy by a viewer on earth (Graphic in Reflections Nov 2018, Mount Wilson Observatory.) Top of page the lower left graphic is J.S. Plaskett’s 1935 profile of the new galaxy model. It shows white clusters outlining a thick galactic center. (Plaskett, Haley Lecture, June 1935, Plate II.) Top of page main image is Needle Galaxy NGC 4565 that we see edge-on, with a wide disk and central bulge. We see its dark dust belt, In our Galaxy Shapley called the dark region the “zone of avoidance.” It was later shown to be obscuring dust. (NGC 4565Mount Lemmon Sky Center, U of Ariz.)
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RESULT 2
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- AND LED TO THE UNIVERSE
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BLOCK F Results - full width 3 bullets
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Other Discoveries SO: this is A list of 5. please indent
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Breakthrough Insights
1911-13 - Russell Diagram of Sellar Evolution (pub 1914, 19x)
Was filled in by Shapley for his 1913 PhD thesis (on 87 systems) and 1914 final (90 systems). Shapley’s enormous volume of data filled in (giants and dwarfs) the main branches postulated by Russell, and published as Hertzsprung Russell Diagram. The intense successful project formed a life-long bond between Shapley, the grad student, and Russell the “dean of American astronomers.”
1920s-1930s Maps of Galaxy Distribution in Southern and Northern Sky. Clusters, superclusters and voids emerged as prominent features, Shapley _ non uniformity of matter, at least to 13th and 18th magnitude. Whether this made the expanding universe ultimately ‘closed’ or ‘open.’ Most prominently With Adelaide Ames 1923-1932 and others as PI and research leader of the observatory’s galactic studies program. link Great Debate
1953 - ca 1968 “We are not alone” There must be xx billion on other planetary systems … link Shapley’s legacies.
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Graphic 6
Graphic 7
Missed Discoveries
“You said that lecture was to be just one hour!” - HS PDF to come
NOTES
SO: RETURN TO ARROW as with Lloyd Work page
Harlow Shapley Science List (PDF)
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