The circle has been known since before the beginning of recorded history. Natural circles would have been observed, such as the Moon, Sun, and a short plant stalk blowing in the wind on sand, which forms a circle shape in the sand.
The circle is the basis for the wheel, which, with related inventions such as gears, makes much of modern machinery possible. In mathematics, the study of the circle has helped inspire the development of geometry, astronomy and calculus.
The state flag of South Korea was adopted in 1950 after the division of the country into the northern and the southern territory. This flag, called taegukki in Korean, has originated in the 19th century. In the middle of the white rectangular background, there is a red-blue symbol of duality and harmony of opposites called yin and yang, where the red part is on top and the blue at the bottom. In each corner of the flag, there is a one trigram (called Kwae) composed of three dashes, or a combination of whole and broken lines. These four trigrams taken from Chinese philosophy are intended to represent the four elements - sky, fire, water, and earth. The white background symbolizes purity, hope and peace.