1. New Astronomical Questions

2. Nature of the Milky Way

3. Nature of the Nebulae

4. Model: Thomas Wright (1750):
Picture motivated by theological considerations
Wright made no new observations.
Model:
Milky Way is a thin spherical shell of stars.
The Sun is located inside the shell about midway between the inner and outer edges.

6. Model: Immanuel Kant (1755):
Misread a newspaper account of Wright's model.
Also made no observations of his own.
Model:
Lens-shaped disk of stars rotating about its center.
No special place for the Sun.
Other "nebulae" are distant, rotating milky ways like ours.
Later became known as the "Island Universe" Hypothesis (term coined by Alexander von Humboldt, Kosmos, 1845).

8. The Herschels' Star Gages
William & Caroline Herschel (1785):
Counted stars along 683 lines of sight using their 20-foot long, 19-inch diameter telescope.
Assumed that stars are uniformly distributed through space, and do not extend beyond the edges of the Milky Way.
Assumed that their telescope could resolve all stars within the boundaries of the Milky Way.

10. Spiral Nebulae are swirling gas clouds
Nebular Hypothesis
Revival of a Solar System model of Pierre Simone Laplace (1796):
Spiral Nebulae are swirling gas clouds
Nearby and internal to our Milky Way
Might be forming solar systems
Big Picture: The Milky Way is the Universe.