MilkyWay - The Milky Way Galaxy Chapter 16 Overview &...

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The Milky Way Galaxy Chapter 16
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Overview & History Our Galaxy is a collection of stellar and interstellar  matter –  stars, gas, dust, neutron stars, black holes stars, gas, dust, neutron stars, black holes  –  held together by gravity. Our view of the Galaxy….
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History of Galactic (& Extragalactic) Astronomy 1610 -Galileo discovered the Milky Way is comprised of many stars 1755 - Immanuel Kant theorized that the galaxy has a planar structure,  some nebulae might actually be entire other galaxies or  island universes 1774 -1781 - Messier catalog compiled including Andromeda galaxy as  M31 1781-1802 - William and Caroline Herschel conducted first “all-sky survey”  and cataloged 5000 nebulae, resolving some into their individual stars Later (1845) William Parsons (Lord Rosse), using a 72-inch telescope,  classified the nebulae into featureless  ellipticals  and whirlpool-like  spiral  nebulae   Much later (1888) Dreyer would add to their list to create the New  General Catalog (NGC) and Index Catalog (IC)
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Herschel could not account well for the effects of dust. Herschel could not account well for the effects of dust. More dust along the disk causes the distribution of stars to drop-off artificially –  objects more than a few kpc from the Sun are obscured by dust. 1785 - Herschel attempted to determine the shape and size of Galaxy Assumptions: All stars have same intrinsic brightness Star are arranged uniformly throughout the MW He could see to the edge of the system            then  d max  = 10 0.2(m_max-M+5) SUN
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•Early 1900’s - Kapteyn used stellar parallax to estimate the true size of the  Galaxy   Kapteyn Universe •10kpc diameter and 2kpc thick with the Sun less than a kpc from the  center (rather heliocentric) •Tried to estimate Rayleigh scattering due to ISM gas but determined  it to be insignificant (because most obscuration is due to ISM  dust  absorption  which has a smaller  λ  dependence) •Shapley (1919) noted that  globular clusters  are distributed asymmetrically in  the sky and that if one assumes they are distributed about the center of the  galaxy, this implies the Sun in not near the center •Estimated distances to GCs using  variable stars and P-M relationship •Concluded size to be 100kpc with  Sun 15kpc from center Still wrong…didn’t account for dust  absorption which makes things look  further away
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Globular Clusters in our Galaxy Shapley realized that  the GCs map out the  true extent of our  galaxy!
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This note was uploaded on 07/11/2011 for the course AST 3019 taught by Professor Sarajedini during the Spring '08 term at University of Florida.

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MilkyWay - The Milky Way Galaxy Chapter 16 Overview &...

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