The Smooth Way Cosmic system.

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The Smooth Way Cosmic system NGC 4103, 55 million LY away edge on winding universe dull dust band 500 LY thick side top focus of world clouded by dust The Smooth Way World (1) Our system, the Smooth Way, is a turning plate of stars circulated over an area
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The Milky Way Galaxy AST 2010: Chapter 24

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NGC 4103, 55 million LY away edge on winding cosmic system dull dust band 500 LY thick AST 2010: Chapter 24

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side top

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focal point of universe darkened by dust AST 2010: Chapter 24

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The Milky Way Galaxy (1) Our world, the Milky Way, is a pivoting plate of stars dispersed over an area around 100,000 LY in breadth around 1,000 LY thick notwithstanding stars, gas and dust are additionally found in the slight circle of the Galaxy The stars around its inside frame an atomic lump AST 2010: Chapter 24

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The Milky Way Galaxy (2) It has 4 noteworthy winding arms in addition to littler goads The significant arms are Cygnus, Perseus, Carina, and a fourth anonymous one, which is difficult to recognize (on opposite side of lump) The 3 named arms are each around 80,000 LY long The Sun is close to the internal edge of a short arm, or goad, called the Orion arm which speaks the truth 15,000 LY long furthermore contains the Orion Nebula AST 2010: Chapter 24

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Spiral Arms Hot blue stars outline winding structure – like Xmas lights on a tree The arms are locales where matter is all the more thickly thought Cool orange and red stars are found in and between winding arms Interstellar dust constrains our perspective in noticeable light to dashed circle

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Why Spiral Arms? Stars circle around focal point of mass of system, similar to planets Kepler’s laws infer stars close to the middle are quicker stars more remote are slower Differential revolution of stars clarifies bended state of winding arms

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Rotation Speeds Inner Parts : Rise from Zero to couple of 100 km/sec Outer Parts : Nearly steady at a couple of 100 km/sec Orbital Period: 240 Myr

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Rotation  Spiral Arms AST 2010: Chapter 24

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Spiral example for billions of years? Winding thickness waves AST 2010: Chapter 24

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Spiral Density Waves: Traffic Jam

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Spherical Structure Nuclear Bulge Many RR Lyrae stars A little gas & dust Galactic Halo: external circle with not very many stars Old metal-poor stars Globular groups Dark matter RR Lyrae Stars

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Galactic Center

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Galaxy Mapping with Radio Waves Radio waves are the best to map the appropriation of hydrogen in the system Their wavelengths are expansive contrasted and the measure of interstellar dust grains and therefore the waves go effortlessly through dust Center of the Galaxy AST 2010: Chapter 24

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Population I : Disk Stars Ordered, generally round circles in a plane All circle in the same general bearing Orbit speeds comparable at a given span Population II : Spheroid Stars Disordered, curved circles at all slants Mix of customary and retrograde circles Wide scopes of orbital paces Stellar Populations

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Population I Location : Disk and Open Clusters Age : Mix of youthful and old stars Composition : Metal rich (generally sun based) 70% Hydrogen 28% Helium ~2% "metals" Environment : Often gas rich, particularly for the youthful stars AST 2010: Chapter 24

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Population II Location : Spheroid and Globular Clusters Ages : Oldest stars, >10 Gyr Composition : Metal Poor (0.1-1% sun based) 75% Hydrogen 24.99% Helium ~0.01% metals Environment : gas poor, no star development AST 2010: Chapter 24

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Population I Disk & open bunches Young & old stars Metal-rich Blue M-S stars Ordered, roundabout circles in a plane Gas-rich environment with late star arrangement Population II Spheroid & globular groups Oldest stars Metal-poor No blue M-S stars Disordered, circular circles in all headings. Practically no gas & dust, and no star arrangement Contrast & Compare AST 2010: Chapter 24

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Mass of the Milky Way Observe orbital period, P, of stars or interstellar matter versus separation, D, from focus Kepler’s third law  time of o rbit dictated by mass inside of circle D 3 = (M system + M sun ) ï‚\' P 2 earth circle  sun’s mass more remote from the galactic focus, the more mass inside of circle FIND: more mass than we see - dim matter corona AST 2010: Chapter 24

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Dark Matter Two conceivable clarifications for the watched revolution: Law of gravity isn\'t right for worlds There is extra matter that doesn’t emanate noticeable radiation ( dull matter ) No proof that gravity carries on diversely The “dark matter” speculation is in this manner favored It could be cocoa midgets, dark gaps, or new outlandish particles Measurements demonstrate around 90% of the mass in the universe is dim matter ! AST 2010: Chapter 24

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Major Parts of the Milky Way AST 2010: Chapter 24

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Galaxy Forma

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