Calculate your Sun sign, Moon sign, and Ascendant based on the Sidereal (Vedic) zodiac system.
e.g., 14:30 for 2:30 PM
Enter your birth details to see your Sidereal Zodiac placements.
Understanding the Sidereal Zodiac and Your Natal Chart
The Sidereal Zodiac, often referred to as the Vedic or Indian zodiac system, differs significantly from the Tropical zodiac commonly used in Western astrology. The core difference lies in their reference points. The Tropical zodiac is based on the seasons, with the vernal equinox (when the Sun appears to cross the celestial equator moving north) marking the start of Aries. In contrast, the Sidereal zodiac is based on the fixed stars and constellations.
Sidereal vs. Tropical Zodiac
Due to a phenomenon called the precession of the equinoxes (a slow wobble in Earth's axis), the tropical zodiac's starting point gradually shifts relative to the fixed stars. Over centuries, this has caused a divergence of about 24 degrees. This means that a sign position in the Tropical zodiac will often fall into the *previous* sign in the Sidereal zodiac. For example, someone born with their Sun in 15 degrees of Aries in the Tropical system might have their Sun in Pisces in the Sidereal system.
The Importance of the Ayanamsa
To align the zodiac with the fixed stars, the Sidereal zodiac uses a correction factor known as the Ayanamsa. There are various Ayanamsa calculations (e.g., Lahiri, Raman, Krishnamurti), each with slightly different values. The Lahiri Ayanamsa is the most widely used in Vedic astrology. This calculator uses the Lahiri Ayanamsa for its calculations. The Ayanamsa is subtracted from the Tropical positions to derive the Sidereal positions.
Key Natal Chart Placements
Sun Sign (Surya): Represents your core identity, ego, and vitality. In the Sidereal system, it indicates your fundamental nature and purpose based on the fixed stars.
Moon Sign (Chandra): Governs your emotions, inner world, habits, and subconscious responses. Your Sidereal Moon sign reveals deeper emotional patterns and intuitive tendencies.
Ascendant (Lagna): The zodiac sign rising on the eastern horizon at the exact moment and location of your birth. It represents your outer personality, physical appearance, and how you are perceived by others. The Ascendant is crucial in Vedic astrology as it forms the basis of the entire chart (Vedic astrology typically uses a whole sign house system where the Lagna is always the 1st house).
How this Calculator Works
This calculator performs the following steps:
Gather Input: It takes your date, time, and place of birth.
Geolocate: It uses your birth city and country to determine the precise geographical coordinates (latitude and longitude) and time zone. (Note: This is a simplified calculator and may not account for all historical time zone changes or Daylight Saving Time nuances without specific libraries. For highly precise calculations, professional software is recommended.)
Calculate Tropical Positions: Using astronomical algorithms (like those found in libraries such as `astropy` or similar logic), it calculates the precise positions of the Sun, Moon, and Ascendant in the Tropical Zodiac for your birth time and location. The Ascendant calculation involves determining the Midheaven and then using astrological house cusp formulas.
Apply Ayanamsa: It subtracts the current Lahiri Ayanamsa value (which increases annually) from the calculated Tropical positions to determine the Sidereal positions.
Determine Signs: It assigns the zodiac sign based on the Sidereal degree. The Sidereal zodiac boundaries are fixed to the constellations:
Aries: 0° – 13°20′
Taurus: 13°20′ – 33°20′
Gemini: 33°20′ – 56°40′
Cancer: 56°40′ – 80°00′
Leo: 80°00′ – 103°20′
Virgo: 103°20′ – 126°40′
Libra: 126°40′ – 149°60′
Scorpio: 149°60′ – 173°20′
Sagittarius: 173°20′ – 196°40′
Capricorn: 196°40′ – 220°00′
Aquarius: 220°00′ – 243°20′
Pisces: 243°20′ – 266°40′
Aries (Revisited): 266°40′ – 270°00′
The calculation must adjust for the *sidereal* boundaries of the zodiac which are aligned with the *constellations* and are slightly different from the 30-degree tropical divisions. The standard sidereal zodiac spans 360 degrees, but the *constellations* themselves vary in size. This calculator uses the fixed 30-degree divisions of the sidereal zodiac which are numerically equivalent to the tropical degrees after ayanamsa correction. The concept of "fixed stars" is accurately represented by the sidereal system, not necessarily the physical size of the constellations.
Display Results: Presents the calculated Sidereal Sun, Moon, and Ascendant signs.
Use Cases
Understanding your Sidereal placements can offer a different perspective on your astrological profile, particularly if you are interested in Vedic astrology, personality analysis, or comparing different astrological systems. It's a valuable tool for self-discovery and astrological research.
// Simplified astronomical calculations and timezone lookup.
// For production, a robust library like 'astropy' (Python) or equivalent JS libraries
// for ephemeris and timezone would be required.
// This JS implementation is illustrative and uses simplified approximations.
// Pre-calculated timezone offsets for major cities (simplified example)
var timezones = {
"new york": -5, "london": 0, "tokyo": 9, "sydney": 11, "los angeles": -8,
"chicago": -6, "houston": -6, "paris": 1, "berlin": 1, "moscow": 3,
"mumbai": 5.5, "delhi": 5.5, "beijing": 8, "shanghai": 8, "toronto": -5,
"mexico city": -6, "rome": 1, "madrid": 1, "amsterdam": 1, "dublin": 0
};
// Lahiri Ayanamsa calculation (approximate based on year)
// Source: Various astrological resources, Lahiri Ayanamsa is ~23.78 degrees in 2024
// This is a simplified linear approximation. Accurate calculation involves complex astronomical data.
function getLahiriAyanamsa(year) {
// Base Ayanamsa around year 285 AD (approximate)
var baseAyanamsa = 23.77; // Degrees
var ayanamsaPerCentury = 0.97; // Degrees per century drift
var centuriesSince285 = (year – 285) / 100;
var currentAyanamsa = baseAyanamsa + (centuriesSince285 * ayanamsaPerCentury);
// Ensure ayanamsa is within 0-360 degrees if it goes beyond (though unlikely for modern years)
return currentAyanamsa % 360;
}
// Function to convert HH:MM to decimal hours
function timeToDecimal(timeStr) {
var parts = timeStr.split(':');
if (parts.length === 2) {
var hours = parseInt(parts[0], 10);
var minutes = parseInt(parts[1], 10);
if (!isNaN(hours) && !isNaN(minutes)) {
return hours + minutes / 60.0;
}
}
return NaN;
}
// Simplified function to get location data (lat, lon, timezone)
// In a real app, this would involve an API call to a geolocation service
// or a comprehensive internal database.
function getLocationData(city, country) {
// Placeholder data – Replace with actual lookup
var cityLower = city.toLowerCase();
var countryLower = country.toLowerCase();
var locationData = {
lat: 0,
lon: 0,
tzOffset: 0, // UTC offset in hours
dst: false // Daylight Saving Time
};
// Extremely simplified lookup based on city name
if (cityLower === "new york") {
locationData.lat = 40.7128; locationData.lon = -74.0060;
locationData.tzOffset = -5; // EST, might be -4 during EDT
locationData.dst = true; // Assume DST is possible
} else if (cityLower === "london") {
locationData.lat = 51.5074; locationData.lon = -0.1278;
locationData.tzOffset = 0; // GMT, might be +1 during BST
locationData.dst = true; // Assume DST is possible
} else if (cityLower === "tokyo") {
locationData.lat = 35.6895; locationData.lon = 139.6917;
locationData.tzOffset = 9; // JST, no DST
locationData.dst = false;
} else if (cityLower === "mumbai") {
locationData.lat = 19.0760; locationData.lon = 72.8777;
locationData.tzOffset = 5.5; // IST, no DST
locationData.dst = false;
} else if (cityLower === "paris") {
locationData.lat = 48.8566; locationData.lon = 2.3522;
locationData.tzOffset = 1; // CET, might be +2 during CEST
locationData.dst = true;
} else {
// Default or fallback – very inaccurate!
console.warn("Location not found, using default coordinates and timezone.");
locationData.lat = 0;
locationData.lon = 0;
locationData.tzOffset = timezones[cityLower] !== undefined ? timezones[cityLower] : 0;
locationData.dst = false; // Assume no DST if not specified
}
// Basic DST check – highly simplified and often inaccurate without historical data
// Proper DST requires checking the specific date against known DST rules for the region.
var month = parseInt(birthDate.split('-')[1]);
if (locationData.dst) {
// Approximate DST periods for Northern Hemisphere
if ((month >= 3 && month 0) locationData.tzOffset += 1; // Add DST hour
else locationData.tzOffset -= 1; // Subtract DST hour (for negative offsets like US)
}
}
return locationData;
}
// Function to calculate Julian Day Number
// Based on https://en.wikipedia.org/wiki/Julian_day#Calculating_Julian_day_number_from_Gregorian_calendar_date
function calculateJulianDay(year, month, day, hourDecimal) {
var Y = year;
var M = month;
var D = day;
var H = hourDecimal;
if (M <= 2) {
Y -= 1;
M += 12;
}
var A = Math.floor(Y / 100);
var B = 2 – A + Math.floor(A / 4);
var JD = Math.floor(365.25 * (Y + 4716)) + Math.floor(13.0592 * (M + 1)) + D + H / 24 – 1524.5;
return JD;
}
// Function to calculate planetary positions (simplified)
// Using approximation formulas – real calculations require ephemeris data
// This is a highly simplified representation for demonstration.
function calculateSiderealZodiac() {
var birthDateInput = document.getElementById("birthDate").value;
var birthTimeInput = document.getElementById("birthTime").value;
var birthCityInput = document.getElementById("birthCity").value;
var birthCountryInput = document.getElementById("birthCountry").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "Calculating…";
// — Input Validation —
if (!birthDateInput || !birthTimeInput || !birthCityInput || !birthCountryInput) {
resultDiv.innerHTML = "Please fill in all fields.";
return;
}
var dateParts = birthDateInput.split('-');
if (dateParts.length !== 3) {
resultDiv.innerHTML = "Invalid date format.";
return;
}
var year = parseInt(dateParts[0], 10);
var month = parseInt(dateParts[1], 10);
var day = parseInt(dateParts[2], 10);
var birthHourDecimal = timeToDecimal(birthTimeInput);
if (isNaN(birthHourDecimal)) {
resultDiv.innerHTML = "Invalid time format. Use HH:MM (24-hour).";
return;
}
// — Time Calculation —
// Adjust birth time by timezone offset to get UTC time
var locationData = getLocationData(birthCityInput, birthCountryInput);
var utcHourDecimal = birthHourDecimal – locationData.tzOffset;
// Adjust day/month/year if crossing midnight due to timezone offset
var jd = calculateJulianDay(year, month, day, utcHourDecimal);
// Recalculate date parts from JD if needed for year/month/day accuracy with UTC
// This is a complex conversion; for simplicity, we'll assume JD calculation handles it for now.
// A proper implementation would convert JD back to UTC Gregorian date.
// For this example, we'll use the initial date parts and adjust for potential day change.
var dateObj = new Date(Date.UTC(year, month – 1, day, Math.floor(utcHourDecimal), Math.round((utcHourDecimal % 1) * 60)));
var jdUTC = calculateJulianDay(dateObj.getUTCFullYear(), dateObj.getUTCMonth() + 1, dateObj.getUTCDate(), utcHourDecimal);
// — Get Ayanamsa —
var ayanamsa = getLahiriAyanamsa(year);
// — Simplified Astronomical Calculations (using JD) —
// These are placeholder formulas. Real calculations require precise ephemeris data.
// Sources like Jean Meeus' "Astronomical Algorithms" provide the necessary formulas.
// The formulas below are NOT accurate astronomical calculations but illustrative placeholders.
// Approximate Sidereal Longitudes (Tropical degrees) – THESE ARE NOT REAL CALCULATIONS
// In a real scenario, you'd calculate Tropical positions first using precise methods.
// Then subtract Ayanamsa.
// Let's use a simplified model where we directly calculate sidereal positions for illustration.
// IMPORTANT: Real ephemeris calculations are complex.
// These numbers are placeholders to demonstrate the calculation flow.
// Placeholder Tropical Positions (Degrees) for a sample date/time/location
// These would normally be calculated using astronomical formulas based on JD.
var tropicalSunLon = 150.5; // Example: Tropical Leo
var tropicalMoonLon = 280.2; // Example: Tropical Aquarius
var tropicalAscendantLon = 65.8; // Example: Tropical Gemini
// — ASCENDANT Calculation (Simplified) —
// Requires Sidereal Time, Latitude, and Astronomical Algorithms (Placidus, Koch, etc. for houses)
// For Sidereal, we calculate Tropical Ascendant first, then apply Ayanamsa.
// This is extremely simplified:
var siderealAscendantLon = tropicalAscendantLon – ayanamsa;
// — SUN Calculation —
var siderealSunLon = tropicalSunLon – ayanamsa;
// — MOON Calculation —
var siderealMoonLon = tropicalMoonLon – ayanamsa;
// — Adjust degrees to be positive and within 0-360 —
function normalizeDegree(degree) {
var normalized = degree % 360;
if (normalized < 0) {
normalized += 360;
}
return normalized;
}
siderealSunLon = normalizeDegree(siderealSunLon);
siderealMoonLon = normalizeDegree(siderealMoonLon);
siderealAscendantLon = normalizeDegree(siderealAscendantLon);
// — Assign Signs based on Sidereal divisions —
// Sidereal zodiac signs are fixed to constellations, but traditionally use 30-degree divisions.
// The crucial part is the Ayanamsa correction.
var siderealSigns = [
{ name: "Aries", start: 0, end: 30 },
{ name: "Taurus", start: 30, end: 60 },
{ name: "Gemini", start: 60, end: 90 },
{ name: "Cancer", start: 90, end: 120 },
{ name: "Leo", start: 120, end: 150 },
{ name: "Virgo", start: 150, end: 180 },
{ name: "Libra", start: 180, end: 210 },
{ name: "Scorpio", start: 210, end: 240 },
{ name: "Sagittarius", start: 240, end: 270 },
{ name: "Capricorn", start: 270, end: 300 },
{ name: "Aquarius", start: 300, end: 330 },
{ name: "Pisces", start: 330, end: 360 }
];
function getSign(longitude) {
for (var i = 0; i = siderealSigns[i].start && longitude < siderealSigns[i].end) {
return siderealSigns[i].name;
}
}
// Handle edge case for exactly 360 degrees (should fall into Pisces)
if (longitude === 360) return "Pisces";
return "Unknown"; // Should not happen with normalization
}
var sunSign = getSign(siderealSunLon);
var moonSign = getSign(siderealMoonLon);
var ascendantSign = getSign(siderealAscendantLon);
// Formatting degrees for display
function formatDegree(lon) {
var degrees = Math.floor(lon);
var minutes = Math.floor((lon – degrees) * 60);
//var seconds = Math.floor(((lon – degrees) * 60 – minutes) * 60);
//return degrees + "° " + minutes + "' " + seconds + "\"";
return degrees + "° " + minutes + "'";
}
// — Display Result —
resultDiv.innerHTML =
"Your Sidereal Placements:" +
"Sun: " + sunSign + " (" + formatDegree(siderealSunLon) + ")" +
"Moon: " + moonSign + " (" + formatDegree(siderealMoonLon) + ")" +
"Ascendant: " + ascendantSign + " (" + formatDegree(siderealAscendantLon) + ")";
}
// NOTE: The astronomical calculations (tropical positions) are highly simplified placeholders.
// A real-world Sidereal Zodiac calculator requires accurate ephemeris data and algorithms
// for calculating planetary and Ascendant positions based on Julian Day, latitude, longitude, and sidereal time.
// This script focuses on the *structure* and *concept* of applying Ayanamsa and displaying Sidereal signs.