First of all he contemplated the sun, moon, and stars, and saw that they all rose in the East, and set in the West; and those lights which went right over his head described a greater circle, whilst those at a greater distance from the vertical point towards the North or South described the lesser circle. So that the least circles which were described by any of the stars were those two which went round the two poles, the one North, the other South, the last of which is the circle of the star Suhail (that is Canopus) and the circle Al-farkadani, which was next the northern.

And, since he lived in an island situated under the equinoctial line, all those circles cut the horizon at right angles and had alike reference to North and South, seeing both the poles appeared to him at once. He observed that when a star arose in a larger circle and another in a lesser, yet they both arose together and set at the same time, and he noticed it to be the case with all stars at all times.