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Chapter 10

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York University
Natural Science
NATS 1745
Robin Metcalfe

Chapter 10: The Universe Beckons Textbook Notes George Ellery Hale, pioneering solar astronomer  He was instrumental in funding and building the World’s leading two telescopes of their day – the 100inch (2.5m) at mount Wilson and the 200inch on Palomar Mountain, San Diego County  Hale’s giant telescope ushered in a new era of astronomy – the study of the structure of the universe  The 100inch was the earliest ‘light buckets; in the world to be used by professional astronomers  Hale went for broke and ordered a 100inch to be cast at a factory in France. The first mirror had bubbles in it  Hale suffered a nervous breakdown  The next mirror broke when it was coming, hence the next nervous breakdown  Colleague Walter Adams climbed up and sliced the dome open to a star filled sky  The telescope pointed at the brilliant planet Jupiter  They looked though, and their faces turned to horror  Instead of a single image they got 6-7 overlapping images  They went to bed to allowed the mirrors to cool down to the temperature and avoid heat current  When they came back, the telescope was a success. William Herschel, trailblazer of star maps as well as the discovery of Uranus Summary: His love of star charts and gridstones led him to almost discover the structure of our galaxy but he renounced it.  Herschel discovered that they were arranged in a gridstone like pattern. His map bears a remarkable resemblance to images of the Milky way Galaxy  He also noted the positions of nebulae, fuzzy patches in the sky. These worried him towards the end of his life he wrote “I must confess … my opinion of the arrangements of the stars has undergone a gradual chance … but a longer experience and a better acquaintance with the nature of nebulas will not allow a general admission of such a principle’  He renounced his gridstone model in his later years, so close to having discovered the structure of our galaxy  His 1785 gridstone map of the milky way shows remarkable resemblance and accuracy  Expressed his scale model in siriometers, his estimated distance to the brilliant star Sirius Lord Rosse, passionate, amateur astronomer, lived in Parsonstown (now birr) in Ireland Summary: Created ‘Leviathan of Parsonstown’ the largest telescope from 1845-1915  He delighted in building bigger and bigger telescopes – culminating in what was to become the worlds largest, with a mirror of 72inches (1.8m)  Not a fan of Lord Rosse was Sir Robert Ball, Professor of Astronomy at Dublin; he said anyone who knew Rosse would know that he was in it for the mechanical process in making a telescope then the actual observations with the telescope when it is completed  Wrong, Rosse went on to makes some extremely important observations of the mysterious nebulas with his “Leviathan of Parsonstown’  Leviathan of Parsonstown was the largest telescope in the world from 1845 to 1917  Rosse drew up beautiful pictures of nebulas Henrietta Leavitt, Young researcher assistant at Harvard College Observatory (1908)  Was pouring fragile glass photographic plates taken by a telescope in Peru  She was searching for stars that change in brightness  She discovered that some of them followed a striking pattern, the brighter the star the longer it took to change brightness  The brightening and fading of these stars matched a naked eye star that had long been known to vary, Leavitt’s work showed that Cepheids could be used to find distances in space. (the principle, identify a distance Cepheid and compare its brightness with a nearby Cepheid that varies in an equal period of time.  Leavitt had proved that two Cepheids witht the same period must be equally luminous so the faintness of the more remote star reveals its distance  She discovered the relationship between the brightness of a Cepheid variable star and its period of variation led to an understanding of the distance scale of the universe  Problem: astronomers didn’t know the distances to any nearby Cepheids  However, as they began to estimate the brilliance of these incredible luminous beacons, astronomers realized they could now get a handle on the most distant objects in the universe Harlow Shapley, Mt. Wilson observatory  Declared of Henrietta: her discovery of the relation of period to brightness is destined to be one of the significant results of steller astronomy  He went to Mt. Wilson Observatory  He decided to study what exactly made Cepheid’s tick  His real passion was Journalism  He took leavitts observations a step further by measuring the distances to globular clusters – dense balls of stars that form a halo around our galaxy.  He discovered that the Milky Way was far larger than previously thought The New Mt. Wilson Observatory attracted wacky characters … Milton Humason, who dropped out of higher education in 1910 and became a mule driver conveying wood and building materials up to the new telescope site, he rapidly became a night assistant and then a top astronomer in his own right Edwin Hubble  Like William Herschel, he had two careers.  He was a brilliant lawyer and a Rhodes scholar at Oxford (and amateur boxer and tank driver)  “I would rather be a second rate astronomer then a first rate lawyer”  He was quickly snapped up by Mt Wilson observatory  Accomplishments in astronomy i) he began to study the mystery of nebulas ii) he found that some were definitely made of stars rather than gas iii) Homing in on nebula NGC 6822, he discovered 11 cepheid variable stars iv) He was able to measure a distance to the nebulas v) It lays 700,000 light years away, far beyond our Milky Way Galaxy which is 100,000 light years across vi) He began to look at other nebula vii) In M33, he found 25 cepheids and estimated 850,000 light years away viii) In M31, yielded a smaller distance ix) They actually lie 3 million light years away from us x) Edwin Hubble established the nature of the ‘spiral nebulae’. They were galaxies like the Milky way, millions of light years distant xi) Astronomers realized that many of the ‘nebulae’ were independent star systems outside our Galaxy, Hubble called them “extragalactic nebulae” but today we call them Galaxies xii) He photographed his galaxies and discovered not all of them were spirals, some were Catherine Wheels of coiled up stars as we know is true in the case of our Milky Way. xiii) These galaxies are brimful young stars and pregnant nebulae tracing our the spiral arms xiv) There were elliptical galaxies: baleful balls of old red stars, with no natal gas and well past menopause xv) Dwarf galaxies complete the set – ragged little irregulars, frantic with starbirth, and dwarf elliptical, which had probably collided up with their host galaxies and been stripped of their building materials in the process xvi) Hubble also discovered that the Universe is expanding  Some of his work had already been done for him Vesto Melvin Slipher, director of Lowell Observatory in Flagstaff Arizona, where pluto would be discovered in 1930 th  He looked at the spectra of several ‘spiral nebulae’ in the early years of the 20 century  Noticed the ‘nebulae’ appeared to be running away
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