Senior high school students' astronomy conceptions were analysed by means of a written questionnaire presented to them during the beginning of the first semester. The main findings were: (1) Most students answered correctly the questions dealing with the following subjects: the day-night cycle, the reason for the different seasons, and the time of the Moon's revolution around the Earth and the Sun. (2) Most students chose their best account for changes in the Moon's phases as the Moon moving around the Earth. Despite that, most students thought that the Moon must be in its full phase in order to get a total solar eclipse. (3) Most students underestimated distances in the Universe and overestimated the Earth's diameter. (4) Most students answered incorrectly the questions dealing with the following subjects: Sun overhead at noon, longitude time zones, and Moon's rotation. (5) Students studying physics succeeded significantly better than their colleagues in some of the subjects that were taught as a part of their optics and mechanics courses.