Enter your birth details to generate your sidereal horoscope chart.
Your Birth Information
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Your Sidereal Horoscope Chart
Sidereal Sun Sign:
Sidereal Moon Sign:
Ascendant (Rising Sign):
Midheaven (MC):
Understanding the Sidereal Horoscope Calculator
The Sidereal Horoscope Calculator helps determine astrological placements based on the sidereal zodiac, which is aligned with the actual constellations in the sky. Unlike the tropical zodiac (commonly used in Western astrology), the sidereal zodiac accounts for the precession of the equinoxes, a slow wobble of the Earth's axis that shifts the vernal equinox point westward against the constellations over time.
Why Use the Sidereal Zodiac?
Many Eastern astrological traditions, such as Vedic astrology (Jyotish), primarily use the sidereal zodiac. It's also gaining traction among Western astrologers who seek a more precise correlation with celestial phenomena. The sidereal system is considered by some to offer a more direct mapping of planetary influences to the star patterns visible at the time of birth.
How the Calculator Works (Simplified Explanation)
This calculator takes your precise birth details (date, time, and location) and performs complex astronomical calculations. The core steps involve:
Julian Date Calculation: Converting your birth date and time into a Julian Date, a continuous count of days since a specific epoch, which is essential for astronomical calculations.
Ephemeris Calculations: Using astronomical algorithms to determine the precise positions of celestial bodies (Sun, Moon, planets) in the sky at the moment of your birth.
Coordinate System Conversion: The calculated positions are initially in a geocentric equatorial coordinate system. These need to be transformed into ecliptic coordinates (longitude and latitude).
Sidereal Time Calculation: Determining the local sidereal time (LST) at your birth location and time. LST is crucial for calculating house systems and the Ascendant/Midheaven.
Ascendant and Midheaven Calculation: The Ascendant (Rising Sign) is the zodiac sign on the eastern horizon at the moment of birth, and the Midheaven (MC) is the highest point in the sky. These are calculated using the LST and your geographic latitude.
Zodiacal Placement: Planets, the Ascendant, and the MC are then placed into the sidereal zodiac constellations. The key difference from the tropical zodiac is the inclusion of the ayanamsa (a pre-calculated correction factor based on the precession of the equinoxes). This shifts the zodiacal degrees.
Key Concepts:
Ayanamsa: The difference in degrees between the tropical and sidereal zodiacs. Different sidereal systems use slightly different ayanamsa values (e.g., Lahiri, Raman, KP). This calculator typically uses a standard ayanamsa like Lahiri.
Sidereal Sun Sign: The constellation the Sun was transiting through at your birth, according to the sidereal zodiac.
Sidereal Moon Sign: The constellation the Moon was transiting through at your birth, according to the sidereal zodiac.
Ascendant (Rising Sign): The sign rising on the eastern horizon at your birth. It represents your outer persona and how you present yourself to the world.
Midheaven (MC): The highest point in the birth chart, representing career, public image, and life direction.
Example Calculation (Illustrative – Actual calculation is complex):
Suppose a person is born on:
Date: October 26, 1990
Time: 14:30 (2:30 PM)
Location: New York City (Latitude: 40.7128° N, Longitude: -74.0060° W)
Timezone: EST (UTC-5)
The calculator would first determine the Universal Time (UT) of birth: October 26, 1990, 19:30 UT. It would then calculate the Julian Day. Using ephemeris data for this precise moment, it finds the positions of the Sun and Moon. Crucially, it applies the ayanamsa correction to these positions to align them with the sidereal constellations. For example, if the Sun in the tropical zodiac is at 2 degrees Scorpio, applying an ayanamsa might shift it to 10 degrees Libra in the sidereal zodiac.
Similarly, the Local Sidereal Time (LST) for New York at that moment is calculated. Using the LST and latitude (40.7128° N), the Ascendant and Midheaven are computed. The calculator then identifies which sidereal constellation corresponds to these calculated degrees.
The result might show a Sidereal Sun in Libra, a Sidereal Moon in Gemini, and an Ascendant in Leo, offering a different perspective than a tropical chart.
// — Astrological Calculation Libraries (Simplified placeholders) —
// In a real-world scenario, you'd use robust astronomical libraries like
// astro-js, swisseph.js, or similar for accurate calculations.
// These are highly simplified placeholders to demonstrate the concept.
var PLANETS = ["Sun", "Moon", "Mercury", "Venus", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune", "Pluto"];
var SIGNS = ["Aries", "Taurus", "Gemini", "Cancer", "Leo", "Virgo", "Libra", "Scorpio", "Sagittarius", "Capricorn", "Aquarius", "Pisces"];
var AYANAMSA_OFFSET = 23.8; // Lahiri Ayanamsa approximation in degrees
// Function to get zodiac sign from ecliptic longitude (in degrees)
// Assumes sidereal zodiac is being used implicitly after ayanamsa adjustment
function getSiderealSign(longitude) {
var signIndex = Math.floor((longitude + AYANAMSA_OFFSET) % 360 / 30);
return SIGNS[signIndex];
}
// Placeholder function for calculating planetary positions
// THIS IS A GROSS SIMPLIFICATION FOR DEMONSTRATION
// Real calculations involve complex orbital mechanics and ephemerides.
function calculatePlanetPositions(year, month, day, hour, minute, timezoneOffset, latitude, longitude) {
var positions = {};
var baseDate = new Date(Date.UTC(year, month – 1, day, hour, minute));
var julianDay = calculateJulianDay(baseDate);
var siderealTime = calculateSiderealTime(julianDay, longitude);
// Simplified: Assign arbitrary longitude based on input values and time
// This is NOT accurate astronomy, just to show structure.
var timeFactor = (hour * 60 + minute) / (24 * 60);
var dayFactor = (day + timeFactor) / 31; // Very rough
positions["Sun"] = (julianDay % 360) * 0.9856 + (dayFactor * 360); // Example pseudo-calculation
positions["Moon"] = (julianDay % 360) * 13.1763966 + (timeFactor * 360 * 2); // Example pseudo-calculation
// Add other planets with similarly flawed logic
positions["Mercury"] = (positions["Sun"] + 30) % 360;
positions["Venus"] = (positions["Sun"] – 20) % 360;
positions["Mars"] = (positions["Sun"] + 90) % 360;
positions["Jupiter"] = (positions["Sun"] + 180) % 360;
positions["Saturn"] = (positions["Sun"] + 270) % 360;
positions["Uranus"] = (positions["Sun"] + 45) % 360;
positions["Neptune"] = (positions["Sun"] + 135) % 360;
positions["Pluto"] = (positions["Sun"] + 225) % 360;
// Normalize longitudes to 0-360
for (var planet in positions) {
positions[planet] = positions[planet] % 360;
if (positions[planet] < 0) {
positions[planet] += 360;
}
}
return positions;
}
// Placeholder for Julian Day calculation
function calculateJulianDay(date) {
var year = date.getUTCFullYear();
var month = date.getUTCMonth() + 1; // Month is 0-indexed
var day = date.getUTCDate();
var hours = date.getUTCHours() + date.getUTCMinutes() / 60 + date.getUTCSeconds() / 3600;
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 + hours / 24;
}
// Placeholder for Local Sidereal Time calculation
// THIS IS A VERY SIMPLIFIED FORMULA
function calculateSiderealTime(julianDay, longitude) {
var GMST = 280.46061837 + 360.98564736629 * (julianDay – 2451545.0);
var LST = GMST + longitude;
return LST % 360 < 0 ? LST % 360 + 360 : LST % 360;
}
// Placeholder for Ascendant calculation
// THIS IS A HIGHLY SIMPLIFIED REPRESENTATION
function calculateAscendant(siderealTime, latitude, year, month, day, hour, minute, timezoneOffset) {
// In reality, this involves complex spherical trigonometry using obliquity of the ecliptic
// and the relationship between LST, latitude, and the ecliptic.
// We'll use a placeholder value that roughly correlates with LST for demonstration.
var ascendantDegree = (siderealTime + 180) % 360; // Extremely rough approximation
// A slightly more involved pseudo-calculation
var hourFactor = (hour + minute/60 + timezoneOffset) / 24; // Local Hour
var roughAsc = (siderealTime / 15) + latitude / 15; // Not mathematically sound, just for variation
ascendantDegree = roughAsc % 360;
if (ascendantDegree < 0) ascendantDegree += 360;
return ascendantDegree;
}
// Placeholder for Midheaven (MC) calculation
// THIS IS A HIGHLY SIMPLIFIED REPRESENTATION
function calculateMidheaven(siderealTime, latitude, year, month, day, hour, minute, timezoneOffset) {
// MC is related to the ecliptic longitude at the meridian.
// It's calculated using the obliquity of the ecliptic and the sidereal time.
// Using a placeholder that is different from Ascendant but related to LST
var mcDegree = (siderealTime + 90) % 360; // Another rough approximation
return mcDegree;
}
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("timezoneOffset").value);
var latitude = parseFloat(document.getElementById("latitude").value);
var longitude = parseFloat(document.getElementById("longitude").value);
var errorMessage = document.getElementById("errorMessage");
errorMessage.innerHTML = ""; // Clear previous errors
// Input Validation
if (isNaN(year) || year < 1 || isNaN(day) || day 31 || isNaN(hour) || hour 23 || isNaN(minute) || minute 59 || isNaN(latitude) || isNaN(longitude) || isNaN(timezoneOffset)) {
errorMessage.innerHTML = "Please enter valid birth details.";
return;
}
if (latitude 90) {
errorMessage.innerHTML = "Latitude must be between -90 and 90.";
return;
}
if (longitude 180) {
errorMessage.innerHTML = "Longitude must be between -180 and 180.";
return;
}
// Basic month-day validation (can be more complex)
var daysInMonth = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
if (year % 4 === 0 && year % 100 !== 0 || year % 400 === 0) {
daysInMonth[2] = 29; // Leap year
}
if (day > daysInMonth[month]) {
errorMessage.innerHTML = "Invalid day for the selected month and year.";
return;
}
// — Calculations —
// NOTE: The planet position calculation here is a highly simplified placeholder.
// Accurate astrological calculations require complex astronomical algorithms and libraries.
// Calculate UTC time first
var birthDateUTC = new Date(Date.UTC(year, month – 1, day, hour, minute));
var utcHour = birthDateUTC.getUTCHours();
var utcMinute = birthDateUTC.getUTCMinutes();
// Calculate Local Sidereal Time
var julianDay = calculateJulianDay(birthDateUTC);
var siderealTime = calculateSiderealTime(julianDay, longitude);
// Calculate Ascendant and Midheaven (using placeholders)
var ascendantLongitude = calculateAscendant(siderealTime, latitude, year, month, day, hour, minute, timezoneOffset);
var midheavenLongitude = calculateMidheaven(siderealTime, latitude, year, month, day, hour, minute, timezoneOffset);
// Calculate Planetary Positions (using placeholder)
// The placeholder function needs to take UT and location into account for a real calculation.
// Here we pass the local time and offset for simplicity in the placeholder function signature,
// but a real function would use UT and then derive LST and other factors.
var planetPositions = calculatePlanetPositions(year, month, day, hour, minute, timezoneOffset, latitude, longitude);
// — Display Results —
var siderealSunSign = getSiderealSign(planetPositions["Sun"]);
var siderealMoonSign = getSiderealSign(planetPositions["Moon"]);
var ascendantSign = getSiderealSign(ascendantLongitude);
var midheavenSign = getSiderealSign(midheavenLongitude);
document.getElementById("siderealSun").innerText = siderealSunSign;
document.getElementById("siderealMoon").innerText = siderealMoonSign;
document.getElementById("ascendantSign").innerText = ascendantSign;
document.getElementById("midheavenSign").innerText = midheavenSign;
document.getElementById("result").style.display = "block";
}