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Mapping the Milky Way: Challenges in Determining Galactic Distances

Understanding our galaxy, the Milky Way, involves overcoming challenges in measuring astronomical distances. Dust can obscure light and complicate observations. To accurately gauge distances, we rely on methods like parallax, standard candles, and binary star metrics. Methods include identifying celestial objects with known luminosity and employing techniques such as the Tully-Fisher relation. Our solar system's location near the Orion Arm highlights our place within the galaxy, orbiting the Galactic Center over vast time scales. This exploration reveals insights into stellar populations and the galaxy's intricate structure.

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Mapping the Milky Way: Challenges in Determining Galactic Distances

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Presentation Transcript

  1. The Milky Way Astronomy 112 Chapter 20

  2. Mapping our galaxy • Determining distances • Difficult because of dust • Blocks light • Dims light • Reddens light • Any distance requires something with a known luminosity • Standard candle

  3. Measuring distances • Direct measurement • The Astronomical Unit (AU) • Parallax • Radar • Only within solar system • Standard rulers

  4. Measuring distances • Standard Candles • Known luminosity/absolute magnitude

  5. Measuring distances • Standard Candles • Known luminosity/absolute magnitude • Calibration – what is M? • Recognition

  6. Measuring distances • Standard Candles • Binary stars • Orbital parameters, masses, mass-luminosity relation • Main Sequence fitting • RR Lyrae stars • A-class HB stars • Distances within galaxy and to globular clusters • For old stellar populations • TRGB • PNLF • GCLF

  7. Measuring distances • Standard Candles • X-ray bursts • Cepheids • Out to about 100 million ly • Not in elliptical galaxies • Novae • Tully Fisher relation • Faster rotational speed is greater luminosity • Type Ia SN • Hubble redshift***

  8. Measuring distances • Large Magellanic Cloud

  9. Measuring distances • Large Magellanic Cloud

  10. Our place in the Milky Way

  11. Our place in the Milky Way

  12. Our place in the Milky Way

  13. Our place in the Milky Way

  14. Our place in the Milky Way

  15. Our place in the Milky Way • We are close to the rim of the Orion arm • In the Local Fluff • 7.94±0.42 kpc from Galactic Center

  16. Where are we going? • Apex of the Sun’s Way • Generally toward Vega • Sun orbits galaxy in 225-250 million years • Galactic year • Thought to have completed about 20-25 orbits since formation • 0.0008 orbit since origin of human species • Orbital speed • 217 km/s • 1 AU in days • 1 ly in 1400 years

  17. Structure of the Milky Way • Parts • Disk • Nuclear bulge • Halo • Globular clusters

  18. Structure of the Milky Way

  19. Structure of the Milky Way • Mapping challenges • We are inside • Distance measurementsare difficult • View toward centerobscured

  20. Structure of the Milky Way • How do we map the galaxy? • Select bright objects • Trace direction & distances • Observe non-visual bands • Circumvent optical extinction • Catalog direction & distance • Trace orbital velocities in different directions

  21. Structure of the Milky Way • How do we map the galaxy? • Star clusters • Open clusters • Young • Distributed evenly through disk • Globular clusters • Old • Centrally located • Mostly in halo

  22. Structure of the Milky Way • Globular clusters • Dense • 50K to 1M stars • Old • ~11 billion years • Lower MS stars • ~200 globular clusters

  23. Structure of the Milky Way • Globular clusters • Distribution is not centered on Sun • Center of distribution is obscured from direct observation

  24. Structure of the Milky Way • Mass • Disk ~200 billion solar masses • Extended halo ~1 trillion • Most matter is no visible • Dark Matter!

  25. Stellar Populations • Metallicity • Population II stars • Absorption lines almost exclusively hydrogen • Metal-poor • e.g. M80 • Population I • Many additional lines

  26. Stellar Populations

  27. Stellar Populations

  28. Age? • and other questions…

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