In spite of its title, this class seems like more than just an introduction. The material starts with the local solar system, and makes its way out in space to the furthest reaches of the known universe, and in time back to the first fraction of a second after the big bang.
The video lectures are first rate, and the instructor is enthusiastic about the material. But the homework is difficult and time-consuming. Unless you have a solid background in algebra and classical mechanics, you're not going to be able to do it. I gave up on doing the homework after four weeks because of the time commitment.
But there's no reason to feel guilty about just "auditing" a class. I thoroughly enjoyed just watching the lectures, and when we got to neutron stars, black holes, galaxies, and the expansion of the universe, every single lecture was mind-blowing!