Understanding frames of reference is critical in describing planetary motion and learning astronomy. Historically, the geocentric and heliocentric models were defended and advocated against each other. Today, there are still many people who do not understand the relationship between the two models. This topic is not adequately treated in astronomy instruction and is unstudied in science education research. The present small-scale study suggests that many science teachers of K-8 hold alternative conceptions about the models of the solar system. Most of the 14 teachers in the study believed that the geocentric model should not be used in classroom instruction because they thought that it was wrong. It was found that they justified their knowledge claims by following common sense, authority, pragmatism, or relativism. Their long-held beliefs, lack of observational experience, and resistance in switching between two models made it difficult for them to have a deep understanding of the relationship of the two models. Specific teaching strategies addressing these learning difficulties on this topic are proposed. (Contains 4 tables, 1 figure, and 4 notes.)