On May 28 at 12:18 PM (local time in Mecca), the sun will be directly overhead the Holy Kaaba, causing vertical objects to cast no shadow in Mecca.
This astronomical event provides a very simple and highly accurate method for determining the Qibla direction.
At that exact moment, in any location in the Northern Hemisphere, one can place a vertical object (such as a stick) upright on level ground.
The shadow cast by the object will point exactly opposite to the direction of the Qibla.
Thus, the Qibla direction is the reverse of the shadow's direction.