I say, and with God's help: It starts from the time of the sun's decline until the shadow of everything reaches twice its length, except for the shadow at noon - which is the shadow that objects have at the time of the sun's decline. The way to determine the time of noon and the shadow at noon is to level the ground so that no part of it is elevated while another part is lowered, which can be measured by pouring water or by setting up specific balances for that purpose. A circle is drawn on it - called the Indian circle - and a vertical measure is set up in its center, ensuring that the distance from its top to three points on the circumference of the circle is equal. This is to ensure that the measure is vertical; if the distance from it to three points on the circumference located at three sides of the circle is equal, then the distance is equal from all directions, indicating that it is upright without tilting. Its height should be a quarter of the radius of the circle; because it is necessary for its shadow to be shorter than half the radius of the circle to distinguish its entry and exit; as the existence of the shadow in most regions can only be imagined in it. The top of its shadow in the early morning is outside the circle, but the shadow decreases until it enters the circle, then a mark is placed at the entry point of the shadow from the circumference of the circle. There is no doubt that the shadow decreases to a certain extent, then increases until it reaches the circumference of the circle and then exits it, which happens after noon. A mark is placed at the exit of the shadow, and the arc between the entry and exit of the shadow is bisected, and a straight line is drawn from the midpoint of the arc to the center of the circle, extending to the other side of the circumference. This line is the noon line; if the shadow of the measure is on this line, it is noon, and the shadow at this time is the shadow at noon. If the shadow moves away from this line, it is the time of noon, which is the first time for the Dhuhr prayer. Its end is when the shadow of the measure becomes twice the measure except for the shadow at noon, for example, if the shadow at noon is a quarter of the measure, the last time for the Dhuhr prayer is when its shadow becomes twice the measure and a quarter of it. See: Fath Bab al-Ianaya 1: 177, and Umdat al-Riaya 1: 145, and God knows best.