 He described a geometrical model for the motion of the Moon and made other astronomical observations of the Moon, Sun and planets using a camera obscura.Some of his beliefs were well wide of the truth, such as his belief that the Milky Way was on the sphere of the fixed stars and shines by the reflected light of the Sun.Gersonides was also the earliest known mathematician to have used the technique of mathematical induction in a systematic and self-conscious fashion and anticipated Galileo's error theory.