Sidereal Sun Sign Calculator
This calculator helps you determine your approximate Sidereal Sun Sign and the Ayanamsa for your birth date. The Sidereal Zodiac, primarily used in Vedic (Jyotish) astrology, accounts for the precession of the equinoxes, unlike the Tropical Zodiac used in Western astrology.
The difference between the two zodiacs is called the Ayanamsa, which slowly increases over time. This calculator uses the Lahiri Ayanamsa system, a widely accepted standard in India.
Understanding the Sidereal Zodiac
The Sidereal Zodiac is fixed against the background stars, meaning the constellations remain in their designated zodiacal positions. In contrast, the Tropical Zodiac is based on the Earth's seasons, with Aries always beginning at the Vernal Equinox (around March 21st).
Due to a phenomenon called the precession of the equinoxes, the Earth's axis slowly wobbles, causing the Vernal Equinox point to shift backward against the backdrop of the stars over thousands of years. This means that the Tropical Zodiac's starting point (0 degrees Aries) is no longer aligned with the constellation Aries.
The Ayanamsa is the angular difference between the Tropical and Sidereal Zodiacs. It represents how far the Tropical 0° Aries has precessed from the Sidereal 0° Aries. This difference grows by approximately 50.29 arcseconds per year.
How to Use This Calculator
- Enter your Birth Year, Month, and Day: This is used to calculate the precise Ayanamsa for your birth date.
- Select your Tropical Sun Sign: This is your standard Western astrology sun sign.
- Enter your Tropical Sun Degree: This is the specific degree within your Tropical Sun Sign (e.g., if you are 15 degrees Aries, enter 15). You can often find this on a Western astrology chart or online birth chart calculator.
- Click "Calculate Sidereal Sun Sign": The calculator will then display your calculated Ayanamsa and your corresponding Sidereal Sun Sign and Degree.
Example Calculation
Let's say someone was born on January 15, 1990, and their Tropical Sun Sign is 25 degrees Capricorn.
- Birth Date: January 15, 1990
- Tropical Sun: Capricorn 25°
- The calculator first determines the Lahiri Ayanamsa for January 15, 1990. This would be approximately 23°38′ (23.63 degrees).
- Capricorn 25° Tropical is equivalent to 270° + 25° = 295° from 0° Aries Tropical.
- To find the Sidereal position, we subtract the Ayanamsa: 295° – 23.63° = 271.37°.
- Converting 271.37° back to a sign and degree:
- 0-29.99° = Aries
- …
- 240-269.99° = Sagittarius
- 270-299.99° = Capricorn
Since 271.37° falls into the Capricorn range, the Sidereal Sun Sign is Capricorn.
- The degree within Capricorn is 271.37° – 270° = 1.37°.
- Therefore, the Sidereal Sun Sign would be Capricorn 1°22′.
As you can see, the Sidereal Sun Sign is often one sign earlier than the Tropical Sun Sign, or sometimes the very beginning of the same sign, depending on the degree and the Ayanamsa.
Limitations
This calculator provides an approximate Sidereal Sun Sign based on the Lahiri Ayanamsa. It does not calculate a full sidereal chart (which includes all planets, houses, and other astrological points) and uses a simplified linear approximation for the Ayanamsa calculation. For a complete and precise sidereal chart, consult a professional Vedic astrologer or specialized astrological software.
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function calculateSiderealSunSign() {
var birthYear = parseInt(document.getElementById("birthYear").value);
var birthMonth = parseInt(document.getElementById("birthMonth").value);
var birthDay = parseInt(document.getElementById("birthDay").value);
var tropicalSignValue = parseInt(document.getElementById("tropicalSign").value);
var tropicalDegree = parseInt(document.getElementById("tropicalDegree").value);
var resultDiv = document.getElementById("result");
// Input validation
if (isNaN(birthYear) || birthYear 2100) {
resultDiv.innerHTML = "
Please enter a valid Birth Year (1800-2100).";
return;
}
if (isNaN(birthMonth) || birthMonth 12) {
resultDiv.innerHTML = "
Please select a valid Birth Month.";
return;
}
if (isNaN(birthDay) || birthDay 31) {
resultDiv.innerHTML = "
Please enter a valid Birth Day (1-31).";
return;
}
// Basic day validation for month
var daysInMonth = new Date(birthYear, birthMonth, 0).getDate();
if (birthDay > daysInMonth) {
resultDiv.innerHTML = "
Invalid Birth Day for the selected Month and Year.";
return;
}
if (isNaN(tropicalSignValue)) {
resultDiv.innerHTML = "
Please select your Tropical Sun Sign.";
return;
}
if (isNaN(tropicalDegree) || tropicalDegree 29) {
resultDiv.innerHTML = "
Please enter a valid Tropical Sun Degree (0-29).";
return;
}
// Lahiri Ayanamsa Calculation (Approximate)
// Reference: Lahiri Ayanamsa on Jan 1, 2000, 12:00 PM UTC is approx 23 degrees 51 minutes (23.85 degrees).
// Precession rate: approx 50.29 arcseconds per tropical year.
var ayanamsa2000 = 23 + (51 / 60); // 23.85 degrees
var precessionRateArcSecPerYear = 50.29;
// Calculate years from epoch (Jan 1, 2000, 12:00 PM UTC) to birth date (12:00 PM UTC assumed)
var epochDate = new Date(Date.UTC(2000, 0, 1, 12, 0, 0));
var birthDate = new Date(Date.UTC(birthYear, birthMonth – 1, birthDay, 12, 0, 0));
var diffMilliseconds = birthDate.getTime() – epochDate.getTime();
var diffDays = diffMilliseconds / (1000 * 60 * 60 * 24);
var yearsFromEpoch = diffDays / 365.24219; // Average length of a tropical year
var ayanamsaDegrees = ayanamsa2000 + (yearsFromEpoch * (precessionRateArcSecPerYear / 3600));
// Convert Ayanamsa to degrees and minutes for display
var ayanamsaDegInt = Math.floor(ayanamsaDegrees);
var ayanamsaMin = Math.round((ayanamsaDegrees – ayanamsaDegInt) * 60);
if (ayanamsaMin === 60) { // Handle rounding up to next degree
ayanamsaDegInt++;
ayanamsaMin = 0;
}
// Calculate Tropical Total Degrees
var tropicalTotalDegrees = tropicalSignValue + tropicalDegree;
// Calculate Sidereal Total Degrees
var siderealTotalDegrees = tropicalTotalDegrees – ayanamsaDegrees;
// Normalize siderealTotalDegrees to be between 0 and 360
siderealTotalDegrees = siderealTotalDegrees % 360;
if (siderealTotalDegrees < 0) {
siderealTotalDegrees += 360;
}
// Determine Sidereal Sign and Degree
var siderealSigns = [
"Aries", "Taurus", "Gemini", "Cancer", "Leo", "Virgo",
"Libra", "Scorpio", "Sagittarius", "Capricorn", "Aquarius", "Pisces"
];
var siderealSignIndex = Math.floor(siderealTotalDegrees / 30);
var siderealSign = siderealSigns[siderealSignIndex];
var siderealDegree = siderealTotalDegrees – (siderealSignIndex * 30);
var siderealDegInt = Math.floor(siderealDegree);
var siderealMin = Math.round((siderealDegree – siderealDegInt) * 60);
if (siderealMin === 60) { // Handle rounding up to next degree
siderealDegInt++;
siderealMin = 0;
if (siderealDegInt === 30) { // If degree becomes 30, it's the next sign
siderealSignIndex = (siderealSignIndex + 1) % 12;
siderealSign = siderealSigns[siderealSignIndex];
siderealDegInt = 0;
}
}
resultDiv.innerHTML = "For your birth date (" + birthMonth + "/" + birthDay + "/" + birthYear + "):" +
"Calculated Lahiri Ayanamsa:
" + ayanamsaDegInt + "°" + ayanamsaMin + "'" +
"Your Sidereal Sun Sign is:
" + siderealSign + " " + siderealDegInt + "°" + siderealMin + "'";
}