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The Path of the Sun and the Changing Seasons

The Middle Path Zhonglu: The celestial equator, or the sun's path during the equinoxes is situated ninety-one and a half degrees and a fraction away from both the North and South Poles. On the day of the Spring Equinox Chunfen: One of the 24 solar terms, marking the moment the sun crosses the celestial equator, the sun travels along this Middle Path. From the Spring Equinox until the Summer Solstice, the sun gradually moves toward the North Path Beilu: The sun's northernmost track, corresponding to the Tropic of Cancer; the Summer Solstice marks the sun's trajectory at this northern limit.

From the Summer Solstice until the Autumn Equinox, the sun turns back from the North Path toward the Middle Path; the Autumn Equinox marks the sun's trajectory upon returning to the center. From the Autumn Equinox until the Winter Solstice, the sun gradually moves toward the South Path Nanlu: The sun's southernmost track, corresponding to the Tropic of Capricorn; the Winter Solstice marks the sun's trajectory at this southern limit. From the Winter Solstice back to the Spring Equinox, the sun turns from the South Path and returns once more to the Middle Path.

Traditional Chinese astronomy divided the sky into "paths" or "circuits" to explain the sun's shifting position. The "Middle Path" equates to the Equator, while the North and South paths represent the sun's position at the solstices.

The varying length of the days—long or short—is due to the relative rising and falling of the Earth This refers to the perceived vertical shift of the sun's path relative to the observer's horizon throughout the year. At the Spring and Autumn Equinoxes, the Earth's position is balanced in the center of the heavens. On these days, the sun rises in the Mao direction original: 卯; the direction of true East and sets in the You direction original: 酉; the direction of true West. Because the sun travels the Middle Path at these times, the lengths of day and night are perfectly equal.

From the Spring Equinox to the Summer Solstice, the "Yang" Sun rises higher while the Earth effectively "descends" In this cosmological model, the sun's path moves "upward" toward the North Pole. During this period, the sun rises in the Yin direction original: 寅; East-Northeast and sets in the Xu direction original: 戌; West-Northwest. Because the sun is traveling the North Path, the days are at their longest.

Conversely, from the Autumn Equinox to the Winter Solstice, the "Yang" Sun descends while the Earth effectively "rises." During this time, the sun rises in the Chen direction original: 辰; East-Southeast and sets in the Shen direction original: 申; West-Southwest. Because the sun is traveling the South Path, the days are at their shortest.

The directions mentioned (Mao, You, Yin, Xu, Chen, Shen) are part of the Twelve Earthly Branches, a system used in ancient China to mark both directions on a compass and hours of the day.