The universe at large

To this point we have been studying the stellar life cycle and how stars and other material are arranged in the Milky Way Galaxy.We will now turn to studies on a much larger scale.We will first look at other galaxies, and see that some of them tell us more about our own galaxy, which is so hard to observe.When we talk about how the universe is put together, each galaxy has only as much importance as a single molecule of oxygen has in describing the gas in your room.

As we go to larger scales, we will look at how galaxies are distributed on the sky, and how they move relative to one another.We will also see how the problem of dark matter becomes more important as we go to larger and larger scales.

As we go to larger scales, increasing the number of galaxies that we observe, we also find a variety of interesting phenomena associated with galaxies. In Chapter 19 we will discuss aspects of galactic activity, particularly as evidenced by radio galaxies and quasars.

In Chapter 20 and 21 we will turn to cosmology, the study of the universe on the largest scales.This also includes the past and future evolution of the universe. It is in the study of the past that we encounter one of the most fascinating aspects of modern astrophysics research, the merging of physics on the smallest (elementary particles) and largest (structure of the universe) scales.

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