The purpose of this study was to investigate preservice science teachers' conceptual understanding of astronomy concepts. Qualitative research methods were used. The sample consists of 118 preservice science teachers (40 freshmen, 31 sophomores, and 47 juniors). The data were collected with Astronomy Conceptual Questionnaire (ACQ) that includes 13 open-ended questionnaires, and measured various aspects of astronomy such as sun, planets, and moon. Moreover, semi-structured interviews were carried out in order to examine further thoughts of the participants. The results indicate that preservice science teachers have several misconceptions about astronomy concepts. Each misconception is generally based on a common incorrect astronomy knowledge. They have also difficulties with basic definitions and interpret visuals of astronomy concepts. Moreover, there is no difference among the levels of students concerning understanding of astronomy concepts.