Galaxies appear in groups and clusters. Their mutual gravity reaches out across unimaginably huge distances to pull them together over cosmic time. As a result, these groups are rich with interactions and varied appearances. We find monster galaxies that cannibalize others and we find the largest gravitationally bound structures of the cosmos.

The Local Group: https://en.wikipedia.org/wiki/Local_G...
M31 in Andromeda: https://en.wikipedia.org/wiki/Androme...
Hickson Compact Groups: https://en.wikipedia.org/wiki/Hickson...
Virgo Cluster: https://en.wikipedia.org/wiki/Virgo_C...
Coma Cluster: https://en.wikipedia.org/wiki/Coma_Cl...
Dark Matter: https://en.wikipedia.org/wiki/Dark_ma...
Intracluster X-Ray Gas: https://en.wikipedia.org/wiki/Intracl...
Superclusters: https://en.wikipedia.org/wiki/Supercl...
The Virgo Supercluster: https://en.wikipedia.org/wiki/Virgo_S...
The Laniakea Supercluster: https://en.wikipedia.org/wiki/Laniake...
Voids: https://en.wikipedia.org/wiki/Void_(a...)
Filaments: https://en.wikipedia.org/wiki/Galaxy_...
The Sloan "Great Wall": https://en.wikipedia.org/wiki/Sloan_G...
Redshift Survey: https://en.wikipedia.org/wiki/Redshif...

0:00 Introduction
0:30 The Local Group
2:35 APOD: 2009, May 10, M31 and M32
2:51 Groups and Clusters of Galaxies
4:25 Hickson Compact Groups
5:04 Virgo Cluster
6:30 Rich Galaxy Clusters
7:27 Coma Cluster
7:47 Abell 02352
8:40 Abell 03496: The Hercules Cluster
9:00 Dark Matter Dominates! Most of the mass of all galaxy clusters is in the form of Duck Matter. This
12:32 X-Ray emitting gas overwhelms the stars
15:00 Superclusters: The Largest Know Structures
16:28 The Virgo Supercluster
17:38 The Laniakea Supercluster
19:32 The Universe on Very Large Scales
20:18 Voids, Filaments and Walls
23:56 The Sloan "Great Wall" Found in the Seas Digital Sky Survey, a large-scale palasy survey. It's a sheet of
26:32 20F Galaxy Redshift Survey
29:51 Cosmography of the Local Universe