An astrological chart, also known as a natal chart, is a snapshot of the sky at the exact moment of your birth. It serves as a cosmic blueprint of your personality, strengths, and life path. While many people only know their "Sun Sign," a true chart calculation involves the precise positions of the planets and the horizon (the Ascendant).
The Importance of the "Big Three"
Sun Sign: Represents your core identity, ego, and basic vitality. It is the essence of who you are.
Moon Sign: Governs your emotional inner world, subconscious patterns, and what makes you feel secure.
Ascendant (Rising Sign): The sign that was rising on the eastern horizon at your birth. It represents your "mask," your first impression on others, and your physical appearance.
How These Calculations Work
To determine your Ascendant, we must calculate the Local Sidereal Time (LST). This involves converting your birth time to UTC, calculating the number of days since the J2000 epoch, and then adjusting for your specific longitude. The mathematical formula used for the Ascendant in this calculator is:
Where e is the obliquity of the ecliptic (~23.44°) and f is your birth latitude. This provides a precise point in the zodiac that defines your first house.
Example Natal Chart Data
If a person was born on March 21, 1990, at 08:00 AM in New York City (Long: -74, Lat: 40.7):
Sun Sign: Aries (The beginning of the zodiac year).
Ascendant: Taurus (Determined by the morning birth time).
Moon Sign: Aquarius (Calculated via the Moon's ~27.3 day orbital cycle).
function calculateChart() {
var dateInput = document.getElementById("birthDate").value;
var timeInput = document.getElementById("birthTime").value;
var tz = parseFloat(document.getElementById("timezone").value);
var lon = parseFloat(document.getElementById("birthLongitude").value);
var lat = parseFloat(document.getElementById("birthLatitude").value);
if (!dateInput || !timeInput || isNaN(lon) || isNaN(lat)) {
alert("Please fill in all birth details including coordinates.");
return;
}
var signs = ["Aries", "Taurus", "Gemini", "Cancer", "Leo", "Virgo", "Libra", "Scorpio", "Sagittarius", "Capricorn", "Aquarius", "Pisces"];
var elements = ["Fire", "Earth", "Air", "Water", "Fire", "Earth", "Air", "Water", "Fire", "Earth", "Air", "Water"];
// 1. Sun Sign Calculation
var d = new Date(dateInput);
var day = d.getDate() + 1; // Correction for input index
var month = d.getMonth() + 1;
var sunSign = "";
if ((month == 3 && day >= 21) || (month == 4 && day = 20) || (month == 5 && day = 21) || (month == 6 && day = 21) || (month == 7 && day = 23) || (month == 8 && day = 23) || (month == 9 && day = 23) || (month == 10 && day = 23) || (month == 11 && day = 22) || (month == 12 && day = 22) || (month == 1 && day = 20) || (month == 2 && day <= 18)) sunSign = signs[10];
else sunSign = signs[11];
// 2. Ascendant Calculation (Simplified Mathematical Model)
var timeSplit = timeInput.split(":");
var hour = parseFloat(timeSplit[0]);
var minute = parseFloat(timeSplit[1]);
// Convert to Universal Time
var ut = hour + (minute / 60) – tz;
// Days since J2000
var year = d.getFullYear();
if (month <= 2) { year -= 1; month += 12; }
var A = Math.floor(year/100);
var B = 2 – A + Math.floor(A/4);
var jd = Math.floor(365.25 * (year + 4716)) + Math.floor(30.6001 * (month + 1)) + day + B – 1524.5 + (ut/24);
var d_j2000 = jd – 2451545.0;
// Greenwich Sidereal Time
var gst = 6.697374558 + 0.0657098244 * d_j2000 + 1.00273791 * ut;
gst = gst % 24;
if (gst < 0) gst += 24;
// Local Sidereal Time
var lst = gst + (lon / 15);
lst = lst % 24;
if (lst < 0) lst += 24;
var ram = lst * 15 * (Math.PI / 180); // RAM in radians
var eps = 23.439 * (Math.PI / 180); // Obliquity
var phi = lat * (Math.PI / 180); // Latitude
var ascRad = Math.atan2(Math.cos(ram), -Math.sin(ram) * Math.cos(eps) – Math.tan(phi) * Math.sin(eps));
var ascDeg = ascRad * (180 / Math.PI);
if (ascDeg < 0) ascDeg += 360;
var ascSignIndex = Math.floor(ascDeg / 30);
var ascSign = signs[ascSignIndex];
// 3. Moon Sign Estimation (Approximate)
// Lunar cycle ~27.32 days. Reference: Jan 1 2000 Moon was in Scorpio (approx 210 deg)
var moonDeg = (210 + (d_j2000 * 13.17639)) % 360;
if (moonDeg < 0) moonDeg += 360;
var moonSign = signs[Math.floor(moonDeg / 30)];
// Display Results
document.getElementById("resSun").innerHTML = sunSign;
document.getElementById("resAsc").innerHTML = ascSign;
document.getElementById("resMoon").innerHTML = moonSign;
document.getElementById("resElement").innerHTML = elements[signs.indexOf(sunSign)];
document.getElementById("resSidereal").innerHTML = lst.toFixed(4) + " hours";
document.getElementById("astroResult").style.display = "block";
}