1 Brief history of the center of the Universe Setting the stage for: The Great Debate Lovers of irony take note Who won? Does it matter? Any take home lessons? Today 2 1 Paid their astronomers to figure out the size of the Universe Fast forward 2200 years to now, guess what? Astronomers still busy trying to figure out the size of the Universe The more things change the more they stay the same? 3 The Universe… The Center of the Universe… Me NOT YOU! 4 2 5 In the sky they saw: the Sun, the Moon, Planets, Stars, some small fuzzy patches, AND ONE BIG FUZZY PATCH Goes from horizon to horizon As a scientist, have to explain that big fuzzy patch in the sky 6 3 Copernicus moves the Sun to the center of the solar system, but keeps the planets moving on circles Kepler finally gets it right (by exhaustion) and puts the planets moving on ellipses Galileo using telescope finds supporting, not conclusive, evidence Phases of Venus Moons of Jupiter Net effect: Center of the Universe moves 93 million miles to the right from the Earth to the Sun 7 The Universe… The Center of the Universe… The Sun NOT YOU! Me 8 4 Galileo also used the telescope to look at the big fuzzy patch in the sky Turned out to be nothing but stars So why are there a lot of stars in a band? Thomas Wright Two concentric spheres In between these spheres are all the stars & our Sun and solar system, a shell of stars Look perpendicular to spheres see few stars Look along shell see more stars Center of the Universe is on the move! 9 The Universe… The Center of the Universe… The Sun 10 5 Charles Messier French astronomer during Comet craze Even with best telescopes of the day some fuzzy patches still fuzzy Real annoying when want to find a comet (another type of fuzzy patch) Came up with a catalogue of 100 fuzzy patches to ignore So don’t look at the following 11 12 6 13 14 7 15 William Hershel English astronomer Surveyed the whole sky and did star counts Saw less stars out of the plane of the Milky Way Decrease in density of stars as got further from the Sun Some of fuzzy patches could be resolved into stars, so assumed that was true for all objects. 16 8 17 The Universe… The Center of the Universe… The Sun NOT YOU! Me 18 9 William Parsons English astronomer mid‐1800’s 72 inch telescope (He was an Earl) Could see some spiral structure in some nebula (fuzzy patches) No way to estimate distance to them (if know distance know size) 19 Jacobus Kapteyn Dutch astronomer at turn of century (1900’s) Did star counts a lá Hershel and came to the same conclusions as Hershel (200 yrs no change) Galaxy flattened disk . 10 kiloparsecs in diameter . 2 kiloparses thick . Sun near center 20 10 But what were those spiral nebula? Galaxies like ours but far, far away? (Island Universes) Or objects within our galaxy (galaxy = universe)? 21 Write “before” on one side & your name And answer the following question: Are science debates useful for . For Science? . For informing the public? 22 11 Prohibition took effect on 16 January Women could vote for President for the first time Communist party completed take over of the U.S.S.R. Population of the U.S. 108 million Total graduating from High School 300,000 60% Women 40% Men Total graduating from College 48,000 66% Men, 33% Women (U of MD enrollment 27,000) 23 Nuclear Fusion unknown This is what powers stars Talk of “subatomic energy” Thought elements common in the Earth dominated the composition of the stars: Oxygen Silicon Iron Stars are 90% H2 & 10% He Thesis of Cecilia Payne in 1925 And later work by Russell on the Sun 24 12 George Ellery Hale (big shot): Funded an annual lecture at the NAS Wanted either: . The size of the universe (galaxy) . Relativity Secretary of the Academy wrote back Size of universe is boring Suggested instead: . Cause of glacial periods . Something biological 25 Hale wrote back, How about relativity then? Secretary of the Academy wrote back: “I would rather have a subject in which there would be a half dozen members of the Academy competent enough to understand at least a few words of what the speakers were saying if we had a symposium upon it” In the end “The Scale of the Universe” was the topic Harlow Shapley Vs. Heber Curtis 26 13 A young ambitious astronomer, a golden boy of astronomy Published a series of papers on properties of stars in binary systems or globular clusters Hale was his boss (and when your boss asks you to do something…) 27 Very nervous Knew Curtis was the better speaker Position of the Director of the Harvard College Observatory had just opened up and he really, really, really wanted the job Talk was essentially a job interview for him 28 14 He was a bit older, more established, the “pro” By far the better speaker Had published a series of papers on the properties of spiral nebulae. Hard worker usually taking the conservative view Frequently skeptical of anything new until proven to his exacting standards. 29 Essentially read his paper: 19 typewritten pages Gave a very elementary general talk, Six pages in finally defines a light year. Focused on the scale of the Galaxy Final three pages are devoted to equipment he developed Irrelevant to his main argument But perhaps directed to those members of the audience responsible for the future development of Harvard College Observatory! 30 15 His model for the Galaxy based upon distribution of globular clusters Globular clusters are concentrated more toward one half of the sky. That half of the sky must be where the true center of our Galaxy is. Got distance to clusters from RR Lyre and Cepheid variable stars 31 Size of the Galaxy Diameter of our Galaxy was 100 kiloparsecs, 10 times larger than Kapteyn’s value! Reality more like 50 kiloparsecs Placement of the Sun Sun 20 kiloparsecs from the Galactic Center So much for being the center of the universe Reality more like 8 kiloparsecs 32 16 What are (where are) the spiral nebulae then? Shapley thought that the Galaxy was so large it was essentially the whole universe. Therefore spiral nebulae are in the galaxy. Knew that the nebulae were moving away from us from spectroscopic observations (red‐shifts). Spiral Nebula are gaseous clouds repelled by the light pressure of our Galaxy (think solar sails) 33 Based his size of galaxy arguments upon: Star count analysis Distance estimates involving the spectral types and intrinsic brightness's of different type stars. Size of the Galaxy Followed Kapteyn : 10 kiloparsecs in diameter Reality more like 50 kiloparsecs (Note (10 + 100)/2 = 55) Sun close to the galactic center 34 17 Disagreed with Shapley that Cepheid variables were good distance indicators (or more like it that more data are needed) What are (where are) the spiral nebulae then? Knew that the nebulae were moving away from us from spectroscopic measurements High radial velocities for the nebulae He argued if they were in the galaxy they would be moving much more slowly relative to the sun. 35 What are (where are) the spiral nebulae then? Novae (Stellar explosions) Novae observed in our Galaxy were similar to novae observed in spiral nebulae But novae in spiral nebulae very faint Implying that the nebulae were very distant & outside the galaxy So the spiral nebulae are systems of stars Therefore our galaxy just one of potentially many galaxies 36 18 Shapley did go on to become director of Harvard’s Observatory Not much attention in the popular or scientific press Who won? Human interest importance? Scientific importance? 37 Shapley –studied globular clusters Better size of galaxy Sun is off to one side Cepheid variables are good distance indicators to globular clusters Curtis –studied spiral nebula Spiral nebulae are really galaxies Novae observed in spiral nebulae are similar to novae observed in our Galaxy 38 19 Here there be dust – Messes up star counts Imagine you are in a very thick fog in a city and can see only one city block in any direction. Can you tell where are you in the city? Explains why globular clusters can be used to find the center of the galaxy 39 Edwin Hubble in 1924 Working at Mount Wilson observatory, where Shapley worked at the time of “The Great Debate” Photographed the Andromeda nebulae & identified a Cepheid variable Which Shapley believed could be used as distance indicators but not Curtis Got a distance to the Andromeda Galaxy of 750 kiloparsecs and size for the Andromeda Galaxy of 70 kiloparsecs ! Showing Curtis was correct about the spiral nebulae 40 20 The Universe courtesy of Shapley The Center of the Universe (galaxy) You are off to one side and only a small part of the Universe 41 The Universe courtesy of Curtis & Shapley & Hubble Galaxy Galaxy Galaxy Galaxy You are off to one side and only a small part of a galaxy 42 21 What makes you feel important? Being the center of everything and everything turns around you? Or being unique, there is one and only one you? Does this effect how you feel about humans? Important, special, unique? Scopes monkey trial 43 Write “after” on the other side Are science debates useful for . For Science? . For informing the public? 44 22 But wait it gets worse! Something similar to “Great Debate” going on today Or the ancient Greeks, take your pick But first to play with blocks 45 Earth Solar System Solar System Sun Either eight, nine, or eleven planets, with moons (some as large as Mercury) Asteroids Comets Gas Dust 46 23 47 48 24 Earth Solar System Galaxy Our Galaxy (Milky Way) All the stars you can see in the night sky .