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Hijri Date:
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Understanding the Hijri Calendar and Conversion
The Hijri calendar (also known as the Islamic calendar or Arabic calendar) is a lunar calendar used by Muslims worldwide to determine the proper days of Islamic holidays and rituals. It consists of 12 months, with the length of each month alternating between 29 and 30 days. The total number of days in a Hijri year is typically 354 or 355 days, which is about 10 to 11 days shorter than a solar (Gregorian) year.
How the Hijri Calendar Works:
Lunar Basis: It is based on the phases of the moon. A new month begins when the new crescent moon is sighted.
Months: There are 12 months: Muharram, Safar, Rabi' al-Awwal, Rabi' al-Thani, Jumada al-Awwal, Jumada al-Thani, Rajab, Sha'ban, Ramadan, Shawwal, Dhu al-Qi'dah, and Dhu al-Hijjah.
Year Length: A common year has 354 days (12 x 29.5 days, approximately). A leap year, which occurs 11 times in a 30-year cycle, has 355 days.
Epoch: The Hijri calendar starts from the year of the Hijra, the migration of Prophet Muhammad (peace be upon him) from Mecca to Medina. This event, which occurred in 622 CE in the Gregorian calendar, marks year 1 AH (Anno Hegirae).
The Challenge of Conversion:
Converting between the Hijri and Gregorian calendars is complex due to their different astronomical bases (lunar vs. solar) and the irregular nature of sighting the moon, which can cause variations in month and year lengths. Precise conversion often relies on intricate algorithms that approximate the lunar cycle or use astronomical data.
How This Calculator Works (Simplified Explanation):
This calculator utilizes a well-established algorithm to perform the conversions. The core idea is to establish a reference point (a known date in both calendars) and then calculate the number of days that have passed since that epoch in each calendar.
Hijri to Gregorian: The algorithm takes the provided Hijri year, month, and day, calculates the total number of days elapsed since the epoch (1 AH). It then uses this total day count to determine the corresponding Gregorian date.
Gregorian to Hijri: Conversely, it calculates the total number of days elapsed since a common reference point for the Gregorian date and then converts this total to the equivalent Hijri date.
These algorithms account for leap years in both systems and the approximate 10.9-day difference per year between the two calendars.
Use Cases:
Islamic Events: Determining the Gregorian dates for Islamic holidays like Ramadan, Eid al-Fitr, and Eid al-Adha.
Historical Research: Correlating historical events recorded in Hijri dates with the Gregorian calendar.
Personal Planning: Scheduling events or understanding personal anniversaries in relation to both calendar systems.
Religious Observances: Ensuring timely observance of prayers, fasting, and other religious duties.
// — Hijri to Gregorian Conversion Logic —
// This is a simplified implementation. For higher accuracy, especially for dates far in the past or future,
// more complex astronomical calculations or lookup tables would be needed.
// This uses a common algorithm approximation.
function convertHijriToGregorian() {
var hijriYear = parseInt(document.getElementById("hijriYear").value);
var hijriMonth = parseInt(document.getElementById("hijriMonth").value);
var hijriDay = parseInt(document.getElementById("hijriDay").value);
var errorDiv = document.getElementById("errorMessage");
var resultDiv = document.getElementById("gregorianResult");
errorDiv.textContent = "";
resultDiv.textContent = "–";
if (isNaN(hijriYear) || isNaN(hijriMonth) || isNaN(hijriDay) ||
hijriYear < 1 || hijriMonth 12 || hijriDay 30) {
errorDiv.textContent = "Please enter valid Hijri date components.";
return;
}
// Basic check for month-day validity (Hijri months can be 29 or 30)
if (hijriDay > 30) {
errorDiv.textContent = "Hijri day cannot exceed 30.";
return;
}
// A more robust check would involve knowing which months have 29 days, which varies.
// For simplicity, we allow 30 and var the conversion algorithm handle potential overflows.
// — Conversion Algorithm (Approximation) —
// This is a common approximation. Reference: https://github.com/ar-prog/hijri-converter
// The calculation is complex and involves epoch dates and day counts.
// Hijri epoch (first day of 1 Muharram 1 AH) corresponds to July 16, 622 CE (Gregorian)
var hijriEpochDays = 1797314; // Days from Gregorian 0001-01-01 to 622-07-16
// Approximate days in Hijri months (average)
var hijriMonthsDays = [0, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29]; // Basic lengths, will be adjusted
var totalHijriDays = 0;
// Add days for full years passed
for (var y = 1; y < hijriYear; y++) {
totalHijriDays += 354; // Assume 354 days, will adjust for leap years later
}
// Add days for full months passed in the current year
for (var m = 1; m < hijriMonth; m++) {
// A more precise algorithm would use pre-calculated month lengths or a more complex leap year logic.
// For simplicity, using a basic length check.
if (m === 2 || m === 4 || m === 6 || m === 8 || m === 10 || m === 12) { // Approximate months with 30 days
totalHijriDays += 30;
} else {
totalHijriDays += 29;
}
}
// Add the days in the current month
totalHijriDays += hijriDay;
// Adjust for leap years in Hijri calendar (approx. 11 leap years in 30 years cycle)
// A leap year adds one day. Roughly: year / 30 = number of 30-year cycles. Each cycle has ~11 leap years.
var leapYears = Math.floor((hijriYear – 1) / 33); // Approximation of leap years count
totalHijriDays += leapYears;
// Total days from Gregorian epoch 0001-01-01
var totalGregorianDays = hijriEpochDays + totalHijriDays;
// Now convert totalGregorianDays to Gregorian date
// This part requires a standard Gregorian date conversion algorithm
var gregorianDate = jdToGregorian(totalGregorianDays);
var gregMonth = gregorianDate.month;
var gregDay = gregorianDate.day;
var gregYear = gregorianDate.year;
// Format the result
var formattedGregorian = gregMonth + "/" + gregDay + "/" + gregYear;
resultDiv.textContent = formattedGregorian;
}
// Helper function for Julian Day to Gregorian Conversion (standard algorithm)
function jdToGregorian(jd) {
var z = Math.floor(jd + 0.5);
var alpha = Math.floor((z – 1867216.25) / 36524.25);
var A = z + 1 + alpha – Math.floor(alpha / 4);
var B = A + 1524;
var C = Math.floor((B – 122.1) / 365.25);
var D = Math.floor(365.25 * C);
var E = Math.floor((B – D) / 30.6001);
var day = B – D – Math.floor(30.6001 * E);
var month = (E 2) ? C – 4716 : C – 4715;
return { year: year, month: month, day: day };
}
// — Gregorian to Hijri Conversion Logic —
// This is a simplified implementation. For higher accuracy, especially for dates far in the past or future,
// more complex astronomical calculations or lookup tables would be needed.
// This uses a common algorithm approximation.
function convertGregorianToHijri() {
var gregorianYear = parseInt(document.getElementById("gregorianYear").value);
var gregorianMonth = parseInt(document.getElementById("gregorianMonth").value);
var gregorianDay = parseInt(document.getElementById("gregorianDay").value);
var errorDiv = document.getElementById("errorMessageGtoH");
var resultDiv = document.getElementById("hijriResult");
errorDiv.textContent = "";
resultDiv.textContent = "–";
if (isNaN(gregorianYear) || isNaN(gregorianMonth) || isNaN(gregorianDay) ||
gregorianYear < 1583 || gregorianMonth 12 || gregorianDay 31) { // Gregorian Proleptic Calendar starts earlier, but for practical purposes
errorDiv.textContent = "Please enter a valid Gregorian date.";
return;
}
// Check day validity based on month
if ((gregorianMonth === 2 && gregorianDay > (isGregorianLeap(gregorianYear) ? 29 : 28)) ||
([4, 6, 9, 11].includes(gregorianMonth) && gregorianDay > 30) ||
([1, 3, 5, 7, 8, 10, 12].includes(gregorianMonth) && gregorianDay > 31)) {
errorDiv.textContent = "Invalid day for the selected Gregorian month and year.";
return;
}
// — Conversion Algorithm (Approximation) —
// This is a common approximation. Reference: https://github.com/ar-prog/hijri-converter
// The calculation is complex and involves epoch dates and day counts.
// Hijri epoch (first day of 1 Muharram 1 AH) corresponds to July 16, 622 CE (Gregorian)
var hijriEpochStartGregorian = 622;
var hijriEpochMonthStartGregorian = 7; // July
var hijriEpochDayStartGregorian = 16;
// Convert Gregorian date to Julian Day Number (JD)
var gregJD = gregorianToJD(gregorianYear, gregorianMonth, gregorianDay);
// Calculate days since Hijri epoch start
var epochJD = gregorianToJD(hijriEpochStartGregorian, hijriEpochMonthStartGregorian, hijriEpochDayStartGregorian);
var daysSinceEpoch = gregJD – epochJD;
// Now convert daysSinceEpoch to Hijri date
var hijriYear = 1;
var hijriMonth = 1;
var hijriDay = 1;
var daysInHijriMonth = [0, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29]; // Base lengths
var remainingDays = daysSinceEpoch;
// Calculate Hijri year and account for leap years
// Approx. 354.37 days per Hijri year
hijriYear = Math.floor(remainingDays / 354.37) + 1;
remainingDays -= (hijriYear – 1) * 354; // Subtract days for full years
// Adjust for leap years (approx. 11 leap years in 30-year cycle)
var leapYearsCount = Math.floor((hijriYear – 1) / 33);
if (remainingDays > 354) { // If calculated year has exceeded basic 354 days, check if it's a leap year adjustment
remainingDays -= leapYearsCount;
if (remainingDays > 354) { // If still exceeding, it means the current year IS a leap year
hijriYear++;
remainingDays -= 355; // Subtract days for a leap year
} else {
remainingDays -= 354; // Subtract days for a common year
}
} else {
remainingDays -= leapYearsCount; // Subtract leap year days if it applies before the current year
if (remainingDays > 354) { // If it implies it's a leap year, adjust
hijriYear++;
remainingDays -= 355;
} else {
remainingDays -= 354;
}
}
// Calculate Hijri month and day
var monthIndex = 1;
while (monthIndex daysInHijriMonth[monthIndex]) {
remainingDays -= daysInHijriMonth[monthIndex];
monthIndex++;
}
hijriMonth = monthIndex;
hijriDay = remainingDays;
// Format the result
var hijriMonthsNames = ["", "Muharram", "Safar", "Rabi' al-Awwal", "Rabi' al-Thani", "Jumada al-Awwal", "Jumada al-Thani", "Rajab", "Sha'ban", "Ramadan", "Shawwal", "Dhu al-Qi'dah", "Dhu al-Hijjah"];
var formattedHijri = hijriMonthsNames[hijriMonth] + " " + hijriDay + ", " + hijriYear + " AH";
resultDiv.textContent = formattedHijri;
}
// Helper function for Gregorian Leap Year Check
function isGregorianLeap(year) {
return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
}
// Helper function for Gregorian to Julian Day Number Conversion
function gregorianToJD(year, month, day) {
var a = Math.floor((14 – month) / 12);
var y = year + 4800 – a;
var m = month + 12 * a – 3;
var jd = day + Math.floor((153 * m + 2) / 5) + 365 * y + Math.floor(y / 4) – Math.floor(y / 100) + Math.floor(y / 400) – 32045;
return jd;
}