Solar Terms & Month Command — Born Hour
The Twenty-Four Solar Terms measure celestial longitude — dividing the sun’s 360° path into 24 exact nodes. In Four Pillars practice, they establish the twelve Month Commands, governing seasonal vitality and elemental rooting.
Solar Terms vs Lunar Calendar
Traditional Chinese timekeeping combines solar and lunar rhythms. While the lunar calendar tracks the moon’s phases (new moon to full moon), the 24 Solar Terms are strictly solar, based on the sun’s celestial longitude from 0° to 360° in 15° increments.
In Four Pillars astrology (BaZi), months are not governed by lunar dates, but strictly by solar terms. Each solar month begins with a Jie (Node) and is anchored by a Qi (Mid-point), defining the seasonal climate.
The 12 Nodes (e.g. Li Chun, Jing Zhe) mark the exact ingress into each of the 12 earthly month branches.
The 12 Mid-points (e.g. Yu Shui, Chun Fen) represent the peak energetic manifestation of the month’s core element.
The Month Branch acts as the planetary climate controller, dictating which elements thrive, weaken, or rest.
The Twelve Month Branches & Seasons
The twelve Earthly Branches correspond directly to the twelve solar months, beginning with Yin in Spring (Li Chun) and concluding with Chou in late Winter (Xiao Han).
Each season is divided into early (Sheng/Growth), peak (Wang/Center), and storage (Mu/Graveyard) phases, creating a cyclic flow of elemental strength.
Solar longitude 315°~330°. Beginning of Spring (year boundary) and Rain Water; Jia wood commands the rising yang.
Solar longitude 345°~0°. Awakening of Insects and Spring Equinox (equal day/night); Yi wood reigns pure and upright.
Solar longitude 15°~30°. Pure Brightness and Grain Rain; Wu earth sustains flourishing wood and acts as Water Tomb.
Solar longitude 45°~60°. Beginning of Summer and Grain Buds; Bing fire ignites with Geng metal in early birth vitality.
Solar longitude 75°~90°. Grain in Ear and Summer Solstice (peak solar day); Ding fire reaches maximum radiant thermal intensity.
Solar longitude 105°~120°. Minor Heat and Major Heat; dry Ji earth harbors latent fire and serves as Wood Tomb.
Solar longitude 195°~210°. Cold Dew and Frost's Descent; dry Wu earth stores autumn yield and serves as Fire Tomb.
Solar longitude 225°~240°. Beginning of Winter and Minor Snow; Ren water takes planetary command nurturing embryonic Jia wood.
Solar longitude 255°~270°. Major Snow and Winter Solstice (return of one yang); pure Gui water holds cold contemplative depth.
Solar longitude 285°~300°. Minor Cold and Major Cold; frozen Ji earth preserves dormant root seeds as Metal Tomb.
Practical Reading Principles
When reading a birth chart, always examine the exact solar term ingress time rather than midnight on the calendar. An ingress occurring at 23:15 changes the month pillar immediately.
Understand hidden stems within each month branch: the month commander determines whether a hidden stem can pierce through to the heaven stems (Tou Gan).