Calculate the positions of planets and key astrological points in the Sidereal zodiac based on your birth details.
Your Birth Information
Your Sidereal Birth Chart
Results will appear here.
Understanding Your Sidereal Astrology Birth Chart
A birth chart, also known as a natal chart, is a snapshot of the sky at the exact moment and location of your birth. It's a fundamental tool in astrology, used to understand your personality, potential strengths, challenges, and life path. While Western astrology primarily uses the Tropical zodiac, Sidereal astrology uses a zodiac that is aligned with the actual constellations of stars.
The primary difference lies in the starting point. The Tropical zodiac begins at the vernal equinox (0° Aries), which is fixed and does not shift relative to the stars. The Sidereal zodiac, however, is based on the current astronomical positions of the constellations. Due to a phenomenon called the "precession of the equinoxes" (a slow wobble of Earth's axis), the vernal equinox point gradually shifts backward through the constellations over thousands of years. This means that the positions of planets and zodiac signs in a Sidereal chart will differ from a Tropical chart, typically by about 24 degrees in the current era.
How the Sidereal Birth Chart is Calculated:
Calculating a sidereal birth chart involves several complex astronomical and astrological steps. While this calculator simplifies the process, the core components are:
Date and Time of Birth: This is the foundation, establishing the specific moment in time for the calculation.
Location of Birth: Latitude and Longitude are crucial for calculating the Ascendant (Rising Sign) and the House system used.
Timezone: This is essential for converting local birth time to Universal Time (UTC), a standard for astronomical calculations. The 'Timezone Offset' input helps adjust for this.
Ephemeris Data: These are astronomical tables that list the precise positions of celestial bodies (Sun, Moon, planets) for specific dates and times. This calculator uses pre-programmed algorithms to approximate these positions.
Precession Adjustment (Ayanamsha): This is the key to the Sidereal zodiac. An "Ayanamsha" is applied to the calculated Tropical positions to shift them into alignment with the current sidereal constellations. There are various Ayanamshas used by different sidereal astrologers (e.g., Lahiri, Raman, Fagan-Allen). This calculator typically uses a commonly accepted approximation (like Lahiri).
House System: The Ascendant (AC) and Midheaven (MC) are calculated based on birth time and location. These points define the cusps of the astrological houses, which divide the sky into 12 segments representing different areas of life. Placidus, Koch, and Whole Sign are common house systems; this calculator will likely use a standard one for demonstration.
Use Cases for a Sidereal Chart:
Individuals may consult a Sidereal chart for various reasons:
Deeper Understanding: To gain a different perspective on astrological interpretations, particularly if they resonate more with the energy of the zodiac signs as aligned with the constellations.
Cross-Cultural Comparison: Many Vedic (Jyotish) astrologers exclusively use the Sidereal zodiac. Comparing Sidereal and Tropical charts can offer richer insights.
Astrological Research: For astrologers and researchers studying the effects of different zodiacal systems.
This calculator provides an approximation of your Sidereal birth chart placements. For a comprehensive and detailed interpretation, it is recommended to consult with a professional astrologer.
function calculateSiderealChart() {
var year = parseInt(document.getElementById("birthYear").value);
var month = parseInt(document.getElementById("birthMonth").value);
var day = parseInt(document.getElementById("birthDay").value);
var hour = parseInt(document.getElementById("birthHour").value);
var minute = parseInt(document.getElementById("birthMinute").value);
var timezoneOffset = parseFloat(document.getElementById("timezone").value);
var longitude = parseFloat(document.getElementById("longitude").value);
var latitude = parseFloat(document.getElementById("latitude").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = 'Calculating…';
if (isNaN(year) || isNaN(month) || isNaN(day) || isNaN(hour) || isNaN(minute) || isNaN(timezoneOffset) || isNaN(longitude) || isNaN(latitude)) {
resultDiv.innerHTML = 'Please enter valid numbers for all fields.';
return;
}
// Basic validation for ranges
if (month 12 || day 31 || hour 23 || minute 59) {
resultDiv.innerHTML = 'Please enter valid date and time values.';
return;
}
// — Simplified Astronomical Calculations (Approximation) —
// This is a highly simplified approximation. Accurate astrological calculations
// require complex astronomical algorithms and ephemeris data.
// We'll use a basic method to demonstrate the concept of sidereal shift.
// Convert local time to UTC
var localDate = new Date(Date.UTC(year, month – 1, day, hour, minute, 0)); // Month is 0-indexed in JS Date
var utcDate = new Date(localDate.getTime() + (timezoneOffset * 60 * 60 * 1000));
var yearUTC = utcDate.getUTCFullYear();
var monthUTC = utcDate.getUTCMonth() + 1; // Adjust back to 1-indexed
var dayUTC = utcDate.getUTCDate();
var hoursUTC = utcDate.getUTCHours();
var minutesUTC = utcDate.getUTCMinutes();
var secondsUTC = utcDate.getUTCSeconds();
// Calculate Julian Day (simplified – for demonstration)
var a = Math.floor((14 – monthUTC) / 12);
var y = yearUTC + 4800 – a;
var m = monthUTC + 12 * a – 3;
var JD = dayUTC + Math.floor((153 * m + 2) / 5) + 365 * y + Math.floor(y / 4) – Math.floor(y / 100) + Math.floor(y / 400) – 32045;
// Approximate position of planets in ecliptic longitude (Tropical)
// These are extremely rough approximations for demonstration.
// Real calculations use complex formulas or ephemeris lookups.
var sunLonTropical = approximateTropicalSunLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC);
var moonLonTropical = approximateTropicalMoonLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC);
var mercuryLonTropical = approximateTropicalPlanetLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC, 1); // Mercury
var venusLonTropical = approximateTropicalPlanetLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC, 2); // Venus
var marsLonTropical = approximateTropicalPlanetLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC, 4); // Mars
var jupiterLonTropical = approximateTropicalPlanetLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC, 5); // Jupiter
var saturnLonTropical = approximateTropicalPlanetLongitude(yearUTC, monthUTC, dayUTC, hoursUTC, minutesUTC, 6); // Saturn
// Calculate Sidereal positions using a simplified Ayanamsha (e.g., Lahiri)
// Lahiri Ayanamsha as of ~2000 AD is approx 23°51′ or ~23.85 degrees.
// This value increases by about 1 minute of arc per year.
// For simplicity, we'll use a fixed offset for demonstration.
var ayanamsha = 23.85; // Approximate Lahiri Ayanamsha for current era
var sunLonSidereal = (sunLonTropical – ayanamsha + 360) % 360;
var moonLonSidereal = (moonLonTropical – ayanamsha + 360) % 360;
var mercuryLonSidereal = (mercuryLonTropical – ayanamsha + 360) % 360;
var venusLonSidereal = (venusLonTropical – ayanamsha + 360) % 360;
var marsLonSidereal = (marsLonTropical – ayanamsha + 360) % 360;
var jupiterLonSidereal = (jupiterLonTropical – ayanamsha + 360) % 360;
var saturnLonSidereal = (saturnLonTropical – ayanamsha + 360) % 360;
// — VERY Basic Ascendant Calculation (requires more complex algorithms) —
// This part is highly simplified and illustrative. Accurate AC calculation
// involves spherical trigonometry (House system calculations).
var ascendantSidereal = calculateApproximateAscendant(JD, longitude, latitude); // This function is a placeholder
// — Format Results —
var resultHTML = "
Planetary Positions (Sidereal)
";
resultHTML += "Sun: " + formatDegrees(sunLonSidereal) + "";
resultHTML += "Moon: " + formatDegrees(moonLonSidereal) + "";
resultHTML += "Mercury: " + formatDegrees(mercuryLonSidereal) + "";
resultHTML += "Venus: " + formatDegrees(venusLonSidereal) + "";
resultHTML += "Mars: " + formatDegrees(marsLonSidereal) + "";
resultHTML += "Jupiter: " + formatDegrees(jupiterLonSidereal) + "";
resultHTML += "Saturn: " + formatDegrees(saturnLonSidereal) + "";
if (ascendantSidereal !== null) {
resultHTML += "Ascendant (AC): " + formatDegrees(ascendantSidereal) + "";
} else {
resultHTML += "Ascendant (AC): Calculation requires advanced algorithms.";
}
resultDiv.innerHTML = resultHTML;
}
// — Placeholder Approximation Functions —
// These are extremely simplified and NOT astronomically accurate.
// For real calculations, you'd use libraries like AstroDwarf, Swiss Ephemeris, etc.
function approximateTropicalSunLongitude(year, month, day, hour, minute) {
// Very rough approximation based on day of year
var dayOfYear = Math.floor((new Date(Date.UTC(year, month – 1, day)) – new Date(Date.UTC(year, 0, 0))) / 86400000);
var totalHours = dayOfYear * 24 + hour + minute / 60;
var longitude = (totalHours / 365.24) * 360; // Rough
return (longitude + 10) % 360; // Offset for demonstration
}
function approximateTropicalMoonLongitude(year, month, day, hour, minute) {
// Even rougher approximation
var dayOfYear = Math.floor((new Date(Date.UTC(year, month – 1, day)) – new Date(Date.UTC(year, 0, 0))) / 86400000);
var totalHours = dayOfYear * 24 + hour + minute / 60;
var longitude = (totalHours / 27.3) * 360; // Moon's orbital period is ~27.3 days
return (longitude + 50) % 360; // Offset for demonstration
}
// Generic planet approximation (using mean orbital periods)
function approximateTropicalPlanetLongitude(year, month, day, hour, minute, planetIndex) {
// planetIndex: 1=Mercury, 2=Venus, 4=Mars, 5=Jupiter, 6=Saturn
var orbitalPeriods = { 1: 88, 2: 225, 4: 687, 5: 4333, 6: 10759 }; // Approximate days
var meanMotion = { 1: 4.09, 2: 1.60, 4: 0.52, 5: 0.084, 6: 0.033 }; // Degrees per day (approx)
var dayOfYear = Math.floor((new Date(Date.UTC(year, month – 1, day)) – new Date(Date.UTC(year, 0, 0))) / 86400000);
var totalDaysSinceEpoch = (new Date(Date.UTC(year, month – 1, day)) – new Date(Date.UTC(1900, 0, 1))) / 86400000; // Approx days since a reference point
var period = orbitalPeriods[planetIndex];
var longitude = (totalDaysSinceEpoch * meanMotion[planetIndex]) % 360;
// Add offsets based on planet and epoch for better (still poor) approximation
var offsets = { 1: 150, 2: 75, 4: 200, 5: 100, 6: 190 };
longitude = (longitude + offsets[planetIndex]) % 360;
return longitude;
}
// Placeholder for Ascendant calculation – THIS IS HIGHLY COMPLEX
function calculateApproximateAscendant(julianDay, longitude, latitude) {
// Accurate Ascendant calculation requires spherical trigonometry,
// Greenwich Sidereal Time (GST), Local Sidereal Time (LST), and house system formulas.
// This is a placeholder and will not produce accurate results.
// A simplified approach might involve looking up tables or using libraries.
// Example: Let's just offset it based on longitude for a *very* rough idea
// In reality, it's dependent on time of day (UTC) and latitude.
// You would first calculate Greenwich Mean Sidereal Time (GMST) from Julian Day.
// GMST = 280.46061837 + 360.98564736629 * (JD – 2451545.0) + 0.000387933 – (JD – 2451545.0)^3/38710000
// Then Local Sidereal Time (LST) = GMST + Longitude (in degrees)
// Then Ascendant is calculated using LST, Latitude, and obliquity of the ecliptic.
// For DEMONSTRATION ONLY, let's assume a relationship with longitude and time
var roughTimeFactor = 15; // Approx degrees per hour of LST
var approximateLST = (julianDay / 1.0027379) % 360; // Extremely simplified LST approximation
var ascendantRough = (approximateLST + longitude + 90) % 360; // Highly inaccurate placeholder
// Return null or a calculated value. Returning null highlights the complexity.
// return ascendantRough;
return null; // Indicating this requires a proper library/algorithm
}
function formatDegrees(decimalDegrees) {
if (decimalDegrees === null) return "N/A";
var sign = decimalDegrees < 0 ? "-" : "";
decimalDegrees = Math.abs(decimalDegrees);
var degrees = Math.floor(decimalDegrees);
var minutes = Math.floor((decimalDegrees – degrees) * 60);
var seconds = Math.floor(((decimalDegrees – degrees) * 60 – minutes) * 60);
// Convert degrees to sign and degree within sign
var zodiacSign = "";
var degreeInSign = 0;
var tropicalSigns = ["Aries", "Taurus", "Gemini", "Cancer", "Leo", "Virgo", "Libra", "Scorpio", "Sagittarius", "Capricorn", "Aquarius", "Pisces"];
var signIndex = Math.floor(degrees / 30);
degreeInSign = degrees % 30;
zodiacSign = tropicalSigns[signIndex];
// Format minutes and seconds with leading zeros
var formattedMinutes = minutes < 10 ? '0' + minutes : minutes;
var formattedSeconds = seconds < 10 ? '0' + seconds : seconds;
// return sign + degrees + "°" + minutes + "'" + seconds + "\"";
return Math.round(degreeInSign * 100) / 100 + "° " + zodiacSign; // More astrological format
}