By observing the sky, recording the Dipper's positions and watching the shadow of the Sun from an
8-foot measurement pole, ancient Chinese astronomers determined the four directions. The direction of sunrise is the East; the direction of sunset is the West; the direction of the shortest shadow is the South and the direction of the longest shadow is the North. At night, the direction of the Polaris star is the North.
They noticed the seasonal changes. When the Dipper points to the East, it’s Spring, when the Dipper points to the South, it’s summer, when the Dipper points to the West, it’s Fall, and when the Dipper points to the North, it’s Winter.
While observing the cycle of the Sun they used the same measurement pole posted at right angles to the ground and recorded positions of the shadow.
Then they found the length of a year is around 365.25 days. Using the sunrise and Dipper positions, they divided the year's cycle into 24 Segments. They used six concentric circles, marking the 24-segment points, divided the circles into 24 sectors and recorded the length of shadow every day. The shortest shadow is found on the day of the Summer Solstice. The longest shadow is found on the day of the Winter Solstice. After connecting each line and dimming the Yin section from Summer Solstice to Winter Solstice, the sun chart looked identical but opposite each other. This became the symbol of transformation, forming the two primal energies of the universe, the opposites that cause constant movement and change.
This cosmic and universal energy is called qi (also known as ki in Japan, Prana to the Hindus, Pneuma to the Greeks, Ankh to the Egyptians, Ruah to the Hebrews, Tane to the Hawaiians, Arunquiltha to the Australian Aborigines and Orenda to the Iroquois). Qi is the air we breathe, the earth's magnetic ﬁeld, the sun's light. Qi is our spirit, qi is our inner strength. Qi is what breathes life into plants, animals, the mountains, and the oceans. Qi moves in a perpetual process of change. Qi accumulates, disperses, expands, and condenses. Qi meanders and spirals. It can best be described as “life’s breath”, or “cosmic breath”. We are all products of and subject to qi's enormous power.
The principles of qi resemble the ﬁeld in quantum physics*.
"Like the quantum ﬁeld, qi is conceived as a tenuous and non-perceptible form of matter which is present throughout space and can condense into solid material objects. The ﬁeld, or qi, is not only the underlying essence of all material objects, but also carries their mutual interactions in the form of waves." 
Qi energy was recorded into a mathematical pattern, the I Ching.
Yin, the Feminine
Yin is the way of the earth. It contracts and condenses. Yin marks the start of the Winter solstice, representing the passive principle in nature exhibited as darkness, cold, and wet. On a human level, yin symbolizes femininity and inertia, quiet and inward. Nothing can be wholly yin, just as nothing can be wholly yang.
Yin - Moon, shade, death, winter, cold, north, night, Earth, stillness, backward, imaginative, intuitive, creative, soft, inactive, quiet, resting, sleeping, taiji, yoga, meditation, watching TV, reading, listening to music, sadness, passivity, mother, daughter, angles, philosophy, religion, colors blue and green.
Yang, the Masculine
Yang is the way of heaven. It expands. Yang marks the start of the Summer solstice, representing the active principle in nature exhibited as light, heat and dryness. On a human side, yang represents masculinity and the positive side of our emotions. Nothing can be wholly yang, just as nothing can be wholly yin.
Yang - Sun, sunlight, life, summer, hot, south, day, heaven, motion, forward, realistic, logical, detail- oriented, hard, active, loud, active, speed, awake, karate, aerobics, football, studying, analytical game-playing, exuberance, aggression, father, son, round, science, mathematics, ﬁnance, colors red and yellow.
*Quantum Physics - provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. The “ﬁeld” may be thought of as extending throughout the whole of space.
 The Tao of Physics, Fritjof Capra, 3rd ed., Shambhala Publications Inc., Boston.  Wikipedia (http://en.wikipedia.org/wiki/Quantum_mechanics)
 Wikipedia (http://en.wikipedia.org/wiki/Quantum_mechanics)