The Scale of The Universe How Big Is It Really?

Background:

Brief History of the Size of the Universe

• Planets thought to define solar system size
• Stars held on spherical shell(s)
• Kepler estimates size of the solar system
• Thomas Wright (1750) makes spherical shell model of the Galaxy
• Kant postulates Galaxy, other galaxies
• Messier sketeches nebulae
• Kant postulates nebular hypothesis for formation of solar system
• Hershel defines Galaxy size with star counts as well as our apparent position in it.
• Parsons resolves spiral nebulae (sees them break up into individual stars
• Kapteyn models the Galaxy based on star counts and star brightnesses.
• Sir James Jeans theorizes that globular clusters are the precursors of spiral nebulae.
• Slipher measures radial velocities of spiral nebulae.
• Energy sources of stars still unknown
• Age of the Earth estimated to be 2 billion years.

Shapley's View of our Galaxy and the Universe in 1920

• Finds Cepheid distances to globular clusters
• Postulates globulars centered on Galaxy center
• Postulates Galaxy 10 times larger than Kapteyn's model
• Postulates spiral nebulae gas clouds repelled by Galaxy
• Believes Van Maanen result of spiral nebulae rotation

Curtis's View of our Galaxy and the Universe in 1920

• Galaxy size similar to Kapteyn's: small and flattened
• Spiral nebulae galaxies just like the Galaxy
• Didn't believe Shapley's Cepheid variable distances

Hubble to the rescue: