This paper presents an analysis of physics teachers' as well as university and high school students' understanding of some astronomy concepts. In recent years, the significance of astronomy teaching in science education has gradually increased. Many research studies indicate that students have misconceptions about the reasons for seasons, the Moon's phases, the Moon's phase in the solar eclipse and the Sun's position. Nevertheless, there have not been many studies reported, which measure students' and especially teachers' beliefs, experiences and understanding and their misconceptions regarding comets, shooting stars, star orbits, astrology, sunspots, and source of solar energy. This is the first aim of the paper. The second is to emphasize the inadequacy of multiple-choice tests, which are commonly used to determine the conceptual understanding and achievement using multi-tier tests such as two-tier tests. To achieve these aims, this study analyses and compares the alternative conceptions of high school and university students, and physics teachers concerning some astronomy subjects. An Astronomy Concept Test (ACT), consisting of two-tier items, was administered to high school students (n = 176), university students (n = 208), and physics teachers (n = 174). The results showed that students' and teachers' test scores are quite low. Besides, participants (even teachers) showed limited understanding of comets, shooting stars, astrology, movement of stars, sunspots, solar energy, moon rotate, and solar and lunar eclipses.