The text book An Introduction to the Sun and Stars is a great book, although there is a lot to it. There are lots of full colour pictures, and scattered through the text are questions to check you're understanding - which is very like the S103 course.
Its very much like the S194 course, but MUCH more detailed. Also the questions you have to answer, such as how many kilograms of hydrogen does the sun consume a year (its about 5.8 × 1011 kg s−1 in case you're interested), are not handed to you on a plate. You are given some figures, but others you may have to find from earlier in the text or deduce from other information and formulae. I find this all quite invigorating at this stage - and I know that may make be a little weird.
Anyway, this first chapter considers observations of the sun and its various components (yes, I thought the sun was just a yellow thing, but its much more complicated than that!). It has pictures of the sun taken in everything from visible light to x-ray to radio waves. It looks at the theoretical structure and what is going on deep in its depths based on what can be seen on the surface.