BİRİNCİ FEN · ÜÇÜNCÜ BÂB · YEDİNCİ FASIL · Birinci Madde
Firstly, it describes the circles and poles established upon the globe.
Know, esteemed one, that astronomical scholars have posited the existence of eight circles and two poles on the globe in order to record events occurring within the universe. Thus, they assume their existence so as to register and follow terrestrial operations. Of these two poles, one is the north pole, and its opposite is the south pole. The assumed eight circles consist of four major circles and four minor circles.
The first of the major circles is the equatorial circle (circle of equinoxes), the second is the zodiacal circle (circle of constellations). The third is the horizon circle (circle of the horizon), and the fourth is the meridian circle (circle of midday).
As their conditions were explained in the preceding passages. The first two of the minor circles are the tropic circles (circles of revolution), and the other two are the polar circles (circles of constellations). Five of these eight circles are parallel to one another, with equal distances between them. Three of them are curved and intersect each other. Two of these – namely, the horizon circle and the meridian circle – are not drawn on the globe but are assumed to be separate and mobile. The others are drawn upon the globe and are fixed.
Regarding the equatorial circle (circle of equinoxes), it is a large circle found upon the globe, lying on the girdle of the great sphere, the equator (circle of midday adjustment). When the sun, through its movement toward the west, reaches it twice annually, day and night equalize in most of the inhabited regions of the earth; and because the movement of the sun’s sphere is equal and direct at this point, it is called the equatorial circle. These are the two times when the sun arrives at the points of equality (point of equinox; March 21st and September 23rd). One marks the beginning of Aries, and the other the beginning of Libra. The equator is the largest of the circles parallel to itself. It is equidistant from the earth’s two poles and divides the globe into the northern and southern hemispheres. The equator intersects the zodiacal circle at two points, which are located at the places of equinox.
Regarding the zodiacal circle, it has been depicted upon the globe and intersects the equator, extending in one direction to each tropic point (Cancer and Capricorn). This extension is called “the greatest inclination” (general inclination), which extends twenty-three and a half degrees towards the south and north. The poles of this circle are also located twenty-three and a half degrees from the pole of the universe. This circle is divided into twelve parts, each being named a constellation as explained in previous passages. Six constellations lie south of the equator, and six lie north of it. Each constellation is divided into thirty degrees, and each degree into sixty minutes. Accordingly, the entire circle is calculated as three hundred sixty degrees, and the positions of the earth are known based on this principle.
Regarding the horizon circle, it is a large, mobile circle that separates the visible part of the universe from its invisible part and defines their boundaries. The top and bottom of the globe are known through it. This horizon circle has many parts. One is the true horizon, which is a large circle dividing the globe into two. Another is the apparent or perceived horizon (sensory horizon), whose condition varies according to the view of the inhabitants of each region; it is a small circle. A third is the straight horizon (straight horizon), which is a large circle belonging to the equator. The sunrise and sunset are found to occur in a straight line on this horizon, hence its name. Another is the inclined horizon (inclined horizon), known as anything other than the straight horizon we mentioned. That is, all inclined horizons are considered to be inclined towards one of the earth’s two poles. Thus, it is accepted that a different horizon exists in every part of the sky and earth. Sunrises and sunsets are inclined on most of them. At the ninth degree latitude – which is where the earth's poles are located – the circles of revolution are considered like millstones. For at the poles (at the ninety-degree region), the horizon and equator overlap, and their poles are counted as adjacent.
“The distance of the apparent or perceived horizon’s diameter is not more than twenty-two thousand five hundred steps on earth,” it is said. Regarding the equatorial circle, it is a mobile, large circle that passes through both poles of the earth and the determined meridian point, intersecting the equatorial circle. It divides the spheres and the globe into two parts; one side is called east, and the other west. The times of midnight and midday are known and determined by means of this. It is possible to consider each part of the equinox and equator as a half-day circle.
Regarding the four minor circles mentioned above, they are parallel to the equator. Two of them are the constellation polar circles (circles of constellation poles). One is the tropic of Cancer (revolution of summer), which marks the beginning of Cancer. The other is the tropic of Capricorn (revolution of winter), which marks the beginning of Capricorn. Thus, terrestrial affairs are recorded by these eight circles we have mentioned.
“Allah, exalted be He, who brings all things into being from nothingness and makes this operation run with a perfect art and possesses wisdom in what He does, is free from all imperfection.”