New Astronomical Questions

Nature of the Milky Way

Nature of the Nebulae

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.

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).

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.

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.