Cosmos
This part of the site covers phenomena that are on a larger scale than our solar system, stars, and exoplanets. It discusses what we know about the structure of our galaxy, including a few phenomena that are observable but do not fit well in the other sections.
The second session covers what we know about other galaxies, including classification systems, sizes, and clustering.
It then goes to a larger scale to talk about what we know about the history of the Universe itself, including the Big Bang theory, subsequent inflation, the Cosmic Microwave Background Radiation, and the two main theories of how large-scale structures formed (bottom-up and top-down).
Finally, the concept behind the possible death of our Universe, whether it will eventually collapse, expand forever, or expand but continuously slow in its expansion.