Shedding Light on Dark Matter (part 1)

Shedding Light on Dark Matter (part 1)
In the fall I'm giving a lecture series on topics ranging from the history of the universe to time travel. Dark Matter is one of those topics.
In this first of 4 part series, I give a brief introduction and go over distinguishing Dark Matter from what isn't Dark Matter.
Next installment deals with properties of matter and Dark Matter and how they apply to baseball.