Thu thập vật liệu. Cắm cọc thẳng đứng trên mặt đất. Chờ khoảng 15-20 phút. Nối các điểm đã đánh dấu.

Given the above summary, write a detailed text in English for it.
Since the sun rises in the east and sets in the west, the shadows it casts will always move in the opposite direction, and you can observe their motions to determine directions. For this method, you will need:  A straight stick that’s between two and five feet long A straight stick that’s about one foot long Two rocks, stones, or other objects (heavy enough that wind won’t blow them around). Place one of the rocks on the ground to mark the tip of the stick’s shadow. The shadow will have moved. Take the second rock and mark the new location of the tip of the stick’s shadow. If you can wait longer, do so, and place more rocks to mark the changing shadow. Either draw a straight line on the ground between the two marks or use the other stick to connect the dots and make a straight line. The shadow moves in the opposite direction of the sun, so this line denotes the east–west line: the first dot represents west and the second dot represents east. Note that this method is only approximate, and can be off by 23 degrees or so at the equator on the first day of winter or summer.  The variance will be more the farther you get from the equator.  For instance, the sun will rise about 33 degrees north of east on the first day of summer at 42 degrees latitude in the northern hemisphere and 33 degrees south of east on the first day of winter.  It rises due east on the first day of spring and fall all over the world.