BİRİNCİ FEN · ÜÇÜNCÜ BÂB · YEDİNCİ FASIL · İkinci Madde
**Article Two**
Concerning the Indian circle, the line of culmination (midday), the line of equidistance, and the direction of the *qibla*.
O esteemed one! Know that astronomers and geometers, following the lead of the Indian philosophers who devised the Indian circle, have determined the line of culmination (meridian), the line of equidistance (east-west line), and the direction of the *qibla*, which is towards Mecca. The easy way to find the lines of culmination and equidistance is as follows: First, you level the ground so that if water were poured upon it, it would flow evenly in all directions. Then, on this leveled surface, draw a circle of any size and erect a perpendicular rod at its center. The length of the rod should be one-fourth the diameter of the circle. To ascertain whether the rod is upright, either measure it with a plumb bob or observe that the distance from the top of the rod to three points on the circumference of the circle is equal. Now, watch before culmination; when the shadow of the head of the rod enters the circle you have drawn, mark the point on the western side towards the periphery. Then, after the time of culmination, mark the point where that end exits the circle on the eastern side.
At that moment, draw a straight line from between the two points you have marked, bisecting the arc of the circle’s circumference which forms its northern boundary. Extend this line through the center to the periphery; this is the meridian line. When the shadow of the rod recedes from the aforementioned line, it marks the beginning of midday. The line was dividing the circle into two halves; draw another straight line from the midpoints of those two halves. This is the east-west line, which intersects the meridian line at a right angle at the center. However, this method yields more accurate results on the longest day of the year, for then there is no difference between the shadow’s entry and exit.
Another way to find the lines of culmination and equidistance is as follows: When it is desired to observe that the sun is at one of the points of equidistance, it emerges from the horizon parallel to the sun's rising or setting shadow and reaches the center of the Indian circle. Around it lies a similar line which is the east-west line; intersecting with it at a right angle at the center is the meridian line. This is also called the line of culmination.
To find the direction of the *qibla*, divide the circumference of the drawn Indian circle into three hundred and sixty parts. Each quarter of these divisions will be ninety parts. Accept this as the horizon of the inhabited region and determine which point on it represents the direction of the *qibla*. Whoever turns towards that point faces the direction of the Most Noble Ka’bah.
The way to know this point is as follows: [88/b] You discover that the longitude of Mecca al-Mukarrama, from the Western Ocean, is seventy-seven degrees from the formerly flourishing islands of Khalidat, now covered by the sea. You also know that it is twenty-two degrees from the equator. Then, you take the latitude and longitude of the inhabited region where the *qibla* direction is to be determined, from the islands of Khalidat and from the equator. If the longitude of this region is equal to the longitude of Mecca and its latitude is less than the latitude of Mecca, then the *qibla* direction of that region is the southern point where the meridian line reaches the horizon. Those who pray there, turning towards the southern point, face directly towards the *qibla*. Our city of Erzurum is an example. For our city lies north of Mecca al-Mukarrama.
If the longitude of the region where the *qibla* direction is to be determined is the same as that of Mecca and its latitude is less than that of Mecca, then the *qibla* direction of that place is the northern point where the meridian line meets the horizon. This applies to Yemen, which lies south of Mecca al-Mukarrama. If a city’s latitude is the same as Mecca’s latitude but its longitude exceeds Mecca’s longitude, then the *qibla* of that city is at the point where the east and west lines meet the horizon. If a city's latitude is the same as Mecca's latitude but its longitude is less than Mecca's longitude, then the *qibla* of that city is at the eastern point where the east and west lines meet the horizon. According to the last two forms described above, another way to find a city’s *qibla* is to observe on a day when the sun is in the eighth degree of the Gemini constellation or the twenty-third degree of the Cancer constellation; take the difference between Mecca's longitude and the longitude of the city where the *qibla* is to be determined, taking one hour for every fifteen degrees of distance and four minutes for every degree.
If the longitude of that city exceeds Mecca’s longitude, then when the sun has passed through half a day by the amount of minutes and hours taken from the difference, the shadow of the rod you erected will fall towards the *qibla* direction. The *qibla* of that city is in the opposite direction of the shadow's trajectory. This applies to the region of Sudan. If a city’s longitude is less than Mecca’s, then at the time when the minutes and hours taken from the difference remain until the sun completes half a day, the rod’s shadow will fall aligned with the *qibla*. The *qibla* again lies in the direction opposite to the shadow. This applies to the regions of Oman. For on the day when the sun is at twelve degrees, the head point falls directly upon the people of Mecca.
If a city's latitude and longitude both exceed Mecca’s latitude and longitude, count westward from the southern point of the Indian circle’s circumference by the amount of excess found between the two longitudes. From the northern point, also count as you counted westward, and join the two adjacent points with a straight line. For in relation to the city accepted as the center of the circle, Mecca al-Mukarrama lies towards the west. (The circle you have drawn) from the western point of the circle, count westward by the amount of excess found between the two latitudes.
When one wishes to determine the direction of prayer (qibla) from a city, one first draws a circle with Mecca at its center, and then draws lines through it, parallel to the meridians and parallels. Then, from the center of that circle, one draws a line passing through the point where those two lines intersect, extending it to the region in question; this is the direction of the qibla.
The deviation of the qibla is the arc between the point where the aforementioned line intersects with the southern point and the western point. The person praying must deviate from the south towards the west by that amount so as to face the qibla directly. In this way, the qibla will be in a southwestern direction, as is the case in lands of Persia (Ājam).
If a city's latitude and longitude are less than those of Mecca, one measures the longitudinal excess eastward from the north and south points, and counts the latitudinal excess northward from the west and east points. The lines are then joined to complete the process. In this way, it will be seen that the qibla direction of the city lies between north and east, as is the case in regions of Abyssinia (Ḥabaş). If a city's longitude is less than Mecca’s longitude and its latitude greater than Mecca’s latitude, one counts the longitudinal excess eastward from the north and south points, and the latitudinal difference southward from the west and east points, joining these with lines to complete the process. Thus, it will be found that the qibla direction of the city lies between south and east, as is the case in lands of Rum (Anatolia).
If a city’s longitude exceeds Mecca's longitude and its latitude is less than Mecca’s latitude, one counts the longitudinal excess westward from the north and south points, and the latitudinal difference northward from the west and east points, joining these with lines to complete the process. In this way, it will be seen that the qibla direction of the city lies between north and west.
The degrees of latitude and longitude for some known cities will be shown in a table at the end of this section.