[00:00]	A Universe of Galaxies
[05:10]	Characterizing Galaxies
[18:21]	Irregular Galaxies
[20:39]	Spiral Galaxies
[26:00]	Blue through Red Spectra
[29:15]	Galaxy Merger - I
[31:21]	Galaxy Merger - II
[34:17]	Merging Galaxies
[41:18]	Elliptical Galaxies
[45:17]	Density Waves

Learning Objectives

1. Understand the distribution of galaxy properties along the Hubble Tuning Fork.
   1. For ellipticals: a smooth structure, no disk, axial ratio determines sub-classification.
   2. For spirals: importance of bulge, strength and tightness of spiral arms within disk all determine sub-classification.
   3. For barred spirals: spiral properties, plus a central bar.
   4. For lenticulars: large bulge, a disk-like structure without spiral arms, for an intermediate classification between elliptical and spiral.
   5. For irregular and peculiar galaxies: non-symmetric distributions of light (train-wreck), possibly caused by interaction with another galaxy.

2. Visualize the basic form of our Milky Way galaxy, and of all spiral galaxies.
   1. A central bulge, made up of old, red stars.
   2. A disk-like structure full of young, blue stars, gas, and dust, characterized by spiral arms.
   3. A diffuse halo of old, red stars, dense globular clusters, and mysterious dark (non-luminous) matter.

3. Visualize the basic form of elliptical galaxies.
   1. A large smooth structure, similar to the central bulge of a spiral galaxy.
   2. The absence of significant gas reservoirs, implying an old population of stars and little potential for future star formation.
   3. High mass, red colours, often found within large clusters of galaxies.
   4. Might form from the merging of two spiral galaxies.