calculate-Easter.ts

/**
 * Calculates the date of Easter Sunday for a given year in the Gregorian calendar.
 *
 * The method used is the Anonymous Gregorian algorithm (also known as Computus),
 * which calculates Easter as the first Sunday after the first ecclesiastical full moon
 * that occurs on or after March 21.
 *
 * @param year The year for which to calculate Easter Sunday (e.g., 2024).
 * @returns A Date object representing Easter Sunday for the given year.
 */
function calculateEaster(year: number): Date {
    // The Golden Number - 1
    const G = year % 19;
    // Century number
    const C = Math.floor(year / 100);
    // Corrections for leap years and moon's orbit
    const H = (C - Math.floor(C / 4) - Math.floor((8 * C + 13) / 25) + 19 * G + 15) % 30;
    // Correction for Sunday
    const I = H - Math.floor(H / 28) * (1 - Math.floor(H / 28) * Math.floor(29 / (H + 1)) * Math.floor((21 - G) / 11));
    // Weekday for the full moon
    const J = (year + Math.floor(year / 4) + I + 2 - C + Math.floor(C / 4)) % 7;
    // Number of days from March 21 to the Paschal full moon
    const L = I - J;
    // Month of Easter
    const month = 3 + Math.floor((L + 40) / 44);
    // Day of Easter
    const day = L + 28 - 31 * Math.floor(month / 4);

    // Return the date of Easter
    return new Date(year, month - 1, day);
}

// Example usage:
const easterDate = calculateEaster(2024);
console.log(`Easter 2024 falls on: ${easterDate.toDateString()}`);