the shapley – curtis debate 26 apr 1920 center of the galaxyhow big is the universe nebula vs....
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The Shapley – Curtis Debate 26 Apr 1920Center of the Galaxy How big is the universeNebula vs. Galaxies Are “nebula” local or distant
Question of Scale—How big is the Galaxy or the Universe?
Are “Nebula” Local or Distant?
Heber Curtis
• Degree in Classical Languages
• Amateur Astronomer @ Napa College
• Ph.D. in Astro from UVa in 1902
• Director of Allegheny Observatory @ Pitt
Heber Curtis
• Sun is at the center of the Milky Way—oops
• Cepheids are not good for distance measurements—oops
• Milky Way size about 10K parsecs—oops
• Nebula are Galaxies beyond the MW--yea
Harlow Shapley
• Missouri to study journalism
• Switched to astronomy• Ph.D. 1913 @ Princeton
under H.N. Russell• Director of Harvard
Observatory• Founder of UNESCO• FBI Investigation
Harlow Shapley
• Galaxy 100K parsecs—oops (too big)
• Sun is 20K parsecs from the center—yea
• Nebula minor gaseous populations in the Milky Way--oops
The Distance Ladder
• Photometric parallax--using geometry to measure distance to nearby stars
• Standard Candles—using decreasing brightness from certain stars to measure distance to nearby galaxies
Cepheid Variables
• Class of stars whose brightness varies with time
• Period is proportional to intrinsic brightness
• Using inverse square law and knowing period distance can be calculated
Cepheid Variables
• Period vs. luminosity discovered by Henrietta Swan Leavitt
• Worked at Harvard classifying stars
• Opened the way for Hubble, Hurtzsprung and Russell
The Great Debate--Resolved
Edwin Hubble• Used Cepheids to show
Andromeda was beyond the Milky Way
• Discovered “Red Shift”—evidence of an expanding universe
• Erased Einstein’s “Cosmological Constant”
Structure of Galaxies
• Hubble’s work led to understanding the structure of galaxies
And to Types of Galaxies