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by: Sophie Stella

physnotes_weeks_12__14.pdf PHYS 104-01

Marketplace > University of St. Thomas > Astronomy > PHYS 104-01 > physnotes_weeks_12__14 pdf
Sophie Stella

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Here are the notes for weeks 12 through 14 of PHYS 104: Astronomy with Dr. Ruch. There wasn't a lot of content left for the end of the school year, so I combined all the new material into one sect...
Dr. Ruch
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This 2 page Class Notes was uploaded by Sophie Stella on Sunday May 15, 2016. The Class Notes belongs to PHYS 104-01 at University of St. Thomas taught by Dr. Ruch in Winter 2016. Since its upload, it has received 17 views. For similar materials see Astronomy in Astronomy at University of St. Thomas.


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Date Created: 05/15/16
PHYS 104: Astronomy Weeks 12 to 14 Course Notes, 4/25 – 5/13 Definitions Spiral Galaxies: Galaxies that are flat and disk-like, with arms and a central bulge or bar. Elliptical Galaxies: Galaxies in globular form, with less dust than a spiral galaxy. The Big Bang: The creation of all space and time. Quarks: Subatomic particles which make up photons and neutrons. Cepheids: Stars in the instability strip of the HR Diagram. Quasars: The centers of very distant galaxies. These are usually 1000x brighter than the Milky Way. There is evidence that none exist anymore. They must consume 17 solar masses to be as luminous as they are. Active Galactic Nuclei: Nearby galactic centers with quasar-like characteristics. I. The Great Debate A. This was a disagreement between Shapley and Curtis about the shape of the Milky Way, and about the shape of the universe as a whole. 1. Shapley said the Milky Way was the entire universe, and it was just very large. a. He said the spiral nebulae are just clouds of gas within the Milky Way. 2. Curtis said the Milky Way is small, with the sun nearly at the center. a. He said spiral nebulae are other galaxies within the Milky Way. B. Neither are right. The Milky Way is one of many galaxies. The Sun is far from the center of the galaxy, and spiral nebulae are not within it. II. Galaxies A. Spirals (3 main components) (they make up about 75% of the large galaxies) 1. Athin disk containing gas, dust, and stars. 2. Acentral bulge of stars. 3. Aspherical halo surrounding the entire thing, containing stars and star clusters. 4. Some spirals contain a central bar that rotates rigidly, connected to the arms of the galaxy. It is speculated that this is the type of galaxy the Milky Way is. B. Ellipticals (are generally found in clusters of other galaxies) 1. Are not disk-shaped. 2. Contain no gas or dust (so no star formation). 3. Are lacking in O and B stars, which die off more quickly. a. Spirals and ellipticals, however, both contain many M stars. 4. The stars have highly elliptical orbits, with no orderly motion. C. Irregulars 1. This category contains every other type of galaxy which doesn't fit into either the spiral or elliptical categories. 2. They are usually small and dusty, but don't spin. D. Supernovas. 1. These are 100x brighter than cepheids. III. Galaxy Evolution A. It is impossible to watch a single galaxy evolve, but we are able to see different galaxies in different stages of evolution. 1. If we look out into space, we are able to see galaxies at an earlier stage in life than they actually are, and this is because it has taken so long for the light to reach us. 2. If a galaxy is redshifted, that means it is moving away from us. If it is blueshifted, it is moving towards us. B. Edwin Hubble came up with a system for galaxy classification 1. Elliptical galaxies are labeled with an E and numbered according to their shape and size. 2. Spiral Galaxies are labeled with an S and also numbered accordingly. 3. Spiral galaxies with a central bar are labeled SB. C. Galaxy formation hypotheses 1. Collapsing cloud of gas (the Top Down model) (also the most probable) a. The early universe starts as hydrogen and helium. b. The places with higher densities begin to condense. c. As this cloud collapses, halo stars begin to form in clusters. d. The cloud has angular momentum, so it begins to spin and the centripital force flattens the gas into a disk. e. If the cloud has less angular momentum, it condenses into an elliptical galaxy. f. The star formation continues in the disk where there is gas, but not in the halo. 2. Hierarchical formation a. smaller galaxies sometimes merge together to form larger ones. IV. Hubble's Law V=HₒD A. The further a galaxy is, the more it is redshifted (the faster it is moving away from us). 1. There is a relationship between velocity and distance. 2. Velocity is measured by the doppler shift (the amount it is redshifted), measured in km/s/Mpc. 3. This does not conclude that we are at the center of the universe, which is highly unlikely. B. The space between galaxies is increasing, but the space within galaxies is not, because they are held together by gravity.


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