The purpose of the study was to diagnose students' misconceptions of a number of basic astronomy concepts, namely, the Universe, the Sun, Comets and Constellations. The study was designed as a mixed method research and the sample was composed of a total of 110 seventh grade students. Data were collected through concept cartoons and interviews. In the concept cartoons prepared for each concept, there were four expressions, one of which is a scientific judgment, while the others were misconceptions. Students were asked to choose one of these expressions and explain why s/he thinks in that way. After the analysis of concept cartoons, semi-structured interviews were conducted with five of the students who were found to hold misconceptions. Findings of the study showed that students held several misconceptions on the concepts being studied. Students had misconceptions mostly about comets and they had limited understanding about constellations. Defining a comet as an image of a dying star falling from the sky was quite common among the students, and the number of students who defined constellations as a group of stars connected by lines among them was considerable. The findings of the study also showed that concept cartoons are functional tools for detecting misconceptions.