ASTRO 1 Chapter Notes - Chapter 23: Hertzsprung–Russell Diagram, Harlow Shapley, Elliptical Galaxy
Document Summary
23-1 when galaxies were first discovered, it was not clear that they lie far beyond the milky way. The great debate: harlow shapley vs. heber d. curtis. Shapley: the nebula is small and within our galaxy; the milky way is the universe. Curtis: the nebula is big and far from us. 23-2 hubble proved that the spiral nebulae are far beyond the milky way. Cepheid variables --> determine the distances to galaxies. Their periods are directly linked to their luminosities. Luminosity vs. period: linear relationship for cepheid variables stars. -> given the period, calculated the original luminosity -compare to the luminosity seen from earth-> distance. Hubble: for luminous stars to appear as dim as they were on his photographs, they must be extremely far away. 23-3 galaxies are classified according to their appearance. Spiral galaxies: arched lanes of stars -- disk. Contain young, hot, blue stars & ongoing star formation. Type b: moderately well-defined spiral arms & moderate-sized central bulge.
