The purpose of study is to investigate the fifth graders' understandings of the basic astronomy concept and, if they have, to define their misconceptions and then to determine what reason/s behind them. For this purpose, two hundred seventy fifth grade students from 6 different schools participated. Randomly selected 45 students performing under the class average and 6 teachers were interviewed to determine what reason/s behind students' misconceptions. The results of the study showed that many 5th graders have some misconceptions, such as Moon moves into the Sun's shadow, Moon only revolves around the Earth, it does not revolve around the Sun because the Moon cannot be seen in the day-light. The reasons are one of reconciling out of school experiences, such as observing the rising and setting sun, seeing stars only at night, school experiences, such as misleading diagrams and inappropriate materials, ambiguous terminology and impropriate teaching methodology used by teacher.