Solar Terms Module

The 24 solar terms are a part of the traditional agricultural calendar, marking distinct periods within a year. Each solar term typically begins on a specific (start) date but represents a period lasting about 15 days until the next solar term starts.

For example, the solar term "Lesser Fullness of Grain" (Tiểu mãn) begins around May 20th in the Gregorian calendar. However, it doesn't end on that day; instead, it lasts until the next solar term, "Grain in Ear" (Mang chủng), which starts around June 5th. Therefore, the "Lesser Fullness of Grain" period is roughly from May 20th to June 5th.

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Retrieve Dates of the 24 Solar Terms

Get Solar Term Dates Within a Range

import { getSolarTermsInRange } from "vietnamese-days";

// If no arguments are passed, it returns the solar term for the current day
console.log(getSolarTermsInRange());
// [{date: '2026-05-29', term: 'lesser_fullness_of_grain', name: 'Tiểu mãn', index: 10}]
// index: Represents the day count within the current solar term, starting from 1

// Query a specific date if only the start date is provided
console.log(getSolarTermsInRange('2026-05-01'));
// [{date: '2026-05-01', term: 'grain_rain', name: 'Cốc vũ', index: 13}]

// Query solar terms within a date range
console.log(getSolarTermsInRange('2026-05-01', '2026-05-06'));
/**
 * =>
 * [
 *   {"date":"2026-05-01","term":"grain_rain","name":"Cốc vũ","index":13},
 *   {"date":"2026-05-02","term":"grain_rain","name":"Cốc vũ","index":14},
 *   {"date":"2026-05-03","term":"grain_rain","name":"Cốc vũ","index":15},
 *   {"date":"2026-05-04","term":"grain_rain","name":"Cốc vũ","index":16},
 *   {"date":"2026-05-05","term":"the_beginning_of_summer","name":"Lập hạ","index":1},
 *   {"date":"2026-05-06","term":"the_beginning_of_summer","name":"Lập hạ","index":2}
 * ]
 */

---

Retrieve Only the Start Dates of Solar Terms

import { getSolarTerms } from "vietnamese-days";

/** Get the array of solar term start dates within a specified range */
const solarTerms = getSolarTerms("2026-05-01", "2026-05-20");
solarTerms.forEach(({ date, term, name }) => {
  console.log(`${name}: ${date}, ${term}`);
});
// Output:
// Lập hạ: 2026-05-05, the_beginning_of_summer
// Tiểu mãn: 2026-05-20, lesser_fullness_of_grain

// If there are no solar terms within the range, return []
console.log(getSolarTerms("2026-05-21", "2026-05-25"));
// Output: []

// Query the solar term for a specific day if no end date is provided
console.log(getSolarTerms("2026-05-20"));
// Output: [{date: '2026-05-20', term: 'lesser_fullness_of_grain', name: 'Tiểu mãn'}]