While the moon usually represents a state of animal confusion or of mental unrest, the sun basically represents the opposite of this. The sun is meant to represent an attained knowledge or a sense of level-headedness about a situation. This is a very personal card, which applies directly to your thoughts though, so it should be carefully dissected whenever it appears on a four point spread. The moon card is there to let you know that your thinking is polluted and your judgment clouded. With no mental unrest, the sun tells you that whatever view you have on a subject is the clearest and least polluted that you can possibly get.
For example, if you were to see the sun card appearing on the area of the four point spread that deals with relationships or romance, then this could be interpreted as an understanding that you've reached about the relationship that is true. Many times in a healthy relationship an occasional argument will spring up and undoubtedly you will have your own opinion. If you see the sun here, then this means that the realization you've reached about the argument is the clear and right answer, though it is up to you what you do with that information. If you have been thinking about asking someone out or thinking about ending a relationship for a while, then the sun card will tell you that whatever your final decision is, it is not going to get much better than the one you're already considering.
The sun card usually appears for people in the finances section of a spread if they are thinking about doing something soon that could lead to a great loss or a great gain in money. If you have been thinking about investing in a certain company for a while now, or thinking about buying stock in a new product, whenever you see the sun card you should rest your decision and place it the way that it is, because it means you are viewing the situation with the finest clarity.
Thinking about quitting your job soon? Thinking about trying out a new field? Well, if this is the case and you think you have reached a really fair decision that takes all aspects into account, then you may see the sun card appearing for you in your spread. This is always a good sign because it tells you that even though you may get thrown a curve ball in the future, you have done the best that you could have with the information that you had on hand.
Finally if you have been considering something health or emotionally related recently, such as whether or not to go on a certain prescription, or whether or not to go out with your friends on Saturday night, if you see the sun card then whatever decision you've reached is the best one you could have reached. The sun card means that you have taken all things into account and made the most informed decision possible. Will it lead to health and happiness? Who knows? But you did the absolute best that you could with everything you were told.