Reenacting the Nguyen Dynasty’s Calendar Distribution Ceremony: The Vital Role of the Lunar Calendar in Vietnam.
The Ban Soc Ceremony: Ancient Calendar Distribution of the Nguyen Dynasty
On the very first day of 2026 at Ngo Mon Square within the historic Hue Imperial Citadel, Thua Thien Hue province officially kicked off the Festival season with a vivid reenactment of the Ban Soc Ceremony.
"Ban Soc" was the traditional calendar-issuing ritual of the Nguyen Dynasty, held periodically at the end of the lunar year. In ancient Vietnam, where agriculture was the backbone of the economy, the calendar held a sacred and vital significance. It was more than just a tool to track dates; it was an indispensable guide for farmers to monitor the seasons and weather patterns to plan their crops effectively. Moreover, the calendar allowed people to anticipate meteorological shifts, helping them prepare for and mitigate the impacts of natural disasters.
Each year, once the Kham Thien Giam (the Imperial Observatory) completed the drafting of the new calendar, the royal court organized the Ban Soc ceremony under the supervision of the Ministry of Rites and the Observatory. The first copies were presented to the Royal Family, followed by distribution to court officials in the capital and provinces, before finally being shared with the common people across the kingdom.
Why the Lunar Calendar Is Important for Wet-Rice Civilizations
(Such as Vietnam and Southern China)
The lunar calendar plays a crucial role in wet-rice–growing countries such as Vietnam and southern China because it closely reflects natural rhythms—including the cycles of the Moon, water, climate, and plant growth—which directly affect rice cultivation.
According to the lunar calendar, each month is marked by several important lunar phases:
- New Moon (the 1st day of the lunar month)
- Full Moon (the 15th day of the lunar month)
- Half Moon (first and last quarter)
These lunar phases have a direct influence on agricultural activities, particularly in traditional farming systems.
Agricultural Impacts of Lunar Phases
- Rice seedling preparation and transplanting
Farmers traditionally avoid transplanting rice during periods when the new moon is too weak or when the full moon is too intense, as these extremes are believed to negatively affect root establishment and growth. - Leafy vegetable cultivation
Crops grown for their leaves are best planted near the new moon, when sap is believed to concentrate in the roots, encouraging stronger leaf development. - Fruit-bearing trees
Fruit trees are typically planted during the waxing moon, when the moon is growing, as this phase is associated with upward energy and reproductive growth.
The 24 Solar Terms in the Lunar-Solar Calendar
In addition to lunar phases, the traditional lunar calendar incorporates 24 solar terms (solar nodes), which are essential for agricultural planning.
To determine these solar terms, the Earth’s orbital plane is divided into 360 degrees.
When the Sun reaches the following longitudes:
0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, 165°,
180°, 195°, 210°, 225°, 240°, 255°, 270°, 285°, 300°, 315°, 330°, and 345°
—each position marks a solar term, resulting in a total of 24 solar terms throughout the year.
These solar terms provide critical guidance on:
- Seasonal climate changes
- Rainfall patterns
- Temperature shifts
- Pest and insect activity
They form the foundation of traditional agricultural timing in East and Southeast Asia.
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