Tropical astrology, the Western standard, ties the zodiac to the seasons: 0 degrees Aries is the point where the Sun sits at the March equinox. Sidereal astrology, used in Vedic (Jyotish) astrology, ties the zodiac to the fixed stars. Because Earth's axis slowly wobbles, the two have drifted apart by about 24 degrees, so many people's sidereal Sun sign is the sign before their tropical one.
Neither zodiac is a mistake. They measure the sky from different starting points, and both are internally consistent. Here's why they differ, how to work out your sidereal sign, and what else changes in a Vedic chart.
Precession: the slow wobble behind the gap
Earth spins like a top, and like a top it wobbles. Its axis traces a slow circle, taking roughly 26,000 years to complete one. Astronomers call this the precession of the equinoxes, and the Greek astronomer Hipparchus is credited with discovering it in the second century BCE.
The effect is that the point where the Sun crosses the celestial equator each March, the spring equinox in the northern hemisphere, slides backward against the background stars by about one degree every 72 years.
Western astrology defines the zodiac by that moving equinox point. Ptolemy, writing in the second century CE, anchored the signs to the equinoxes and solstices, and the Western tradition kept that choice. Aries always begins at the March equinox, so tropical Aries is always the first month of northern spring.
Sidereal astrology instead anchors the zodiac to the stars, so its Aries stays put while the equinox drifts away from it. Around the early centuries CE the two zodiacs were close to lined up. Since then they've separated by about a degree every 72 years, which is how they reached today's gap of about 24 degrees.
Which sign are you in sidereal astrology?
The quick rule: subtract about 24 degrees from your tropical position.
- If your tropical Sun is in the first 24 degrees or so of its sign, your sidereal Sun is in the previous sign.
- If it's in the last 6 degrees or so, your sidereal Sun is in the same sign.
A worked example. Someone born around May 5 has a tropical Sun at about 15 degrees Taurus. Subtract 24 degrees and you get about 21 degrees Aries: a Taurus in Western astrology, an Aries in Vedic. Someone born around May 17 has a tropical Sun near 27 degrees Taurus. Subtract 24 and they're at about 3 degrees Taurus: a Taurus in both.
Approximate sidereal Sun sign dates, using the Lahiri system common in Vedic astrology (they shift by a day or so from year to year):
- Aries: about April 14 to May 14
- Taurus: about May 15 to June 14
- Gemini: about June 15 to July 15
- Cancer: about July 16 to August 16
- Leo: about August 17 to September 16
- Virgo: about September 17 to October 16
- Libra: about October 17 to November 15
- Scorpio: about November 16 to December 15
- Sagittarius: about December 16 to January 13
- Capricorn: about January 14 to February 11
- Aquarius: about February 12 to March 13
- Pisces: about March 14 to April 13
The Sun's move into sidereal Capricorn around January 14 is celebrated in India as Makar Sankranti, one place where the sidereal zodiac appears on the everyday calendar. For your exact tropical positions, start with a free birth chart, which uses the tropical zodiac.
Ayanamsas: why sidereal astrologers disagree slightly
The gap between the zodiacs is called the ayanamsa, and sidereal astrologers don't all agree on its exact size, because they don't agree on exactly which star marks the start.
The most widely used is the Lahiri ayanamsa, which fixes the bright star Spica at 0 degrees Libra. It was recommended by India's Calendar Reform Committee in the 1950s and is the standard in most Indian astrology. Western sidereal astrologers often use the Fagan-Bradley ayanamsa, developed by Cyril Fagan and Donald Bradley in the twentieth century. Other systems exist, and the main ones differ from each other by around a degree.
That only matters if a planet sits within a degree of a sign boundary, but if yours does, it's worth knowing which ayanamsa a chart uses.
Is either zodiac right?
They answer different questions. The tropical zodiac describes the Sun's relationship to the seasons and Earth's own cycle: solstices, equinoxes, the lengthening and shortening of days. The sidereal zodiac describes the Sun's position against the stars.
Neither is the same as the constellations. Both zodiacs use twelve equal signs of 30 degrees, while the actual constellations are different sizes and, by modern astronomical boundaries, the Sun passes through thirteen of them. Our guide to Ophiuchus, the "13th sign" explains that separate argument.
People often ask about the southern hemisphere, where March brings autumn rather than spring. In practice, astrologers there use the same tropical zodiac, measured from the same equinox point. Our explainer on what your sun sign is and isn't covers more of that history, and this site's horoscopes and zodiac signs pages use the tropical zodiac throughout.
What changes in a Vedic chart besides the Sun sign
Switching zodiacs moves everything by about 24 degrees: your Moon, your planets and your rising sign too. Many people find their Vedic Moon sign or rising sign changes as well as their Sun.
Vedic astrology also differs in emphasis:
- The Moon sign often leads. The Moon's sign, or rashi, is usually given more weight than the Sun's. You can find your tropical Moon with the moon sign calculator and subtract about 24 degrees.
- Nakshatras. The zodiac is also divided into 27 lunar mansions of 13 degrees 20 minutes each, and the Moon's nakshatra at birth is a central feature of the chart.
- Whole sign houses are common, with each house a complete sign.
- Traditional planets. Classical Vedic astrology uses the seven visible planets plus Rahu and Ketu, the lunar nodes, rather than Uranus, Neptune and Pluto.
- Dashas. Timing is read through planetary periods, the best known being the 120-year Vimshottari cycle.
So a Vedic reading isn't a Western reading with the signs relabeled. It's a different tradition, with its own logic.
Questions readers ask
Is sidereal astrology more accurate than tropical?
Neither has been shown to be more accurate, and astrology as a whole isn't a science. They use different reference points. Tropical follows the seasons, sidereal follows the stars, and practitioners of each find their system meaningful.
Why is my Vedic sign different from my Western sign?
Because the sidereal zodiac used in Vedic astrology sits about 24 degrees behind the tropical one. Unless your Sun is in the last few degrees of a sign, your Vedic Sun sign is usually the sign before your Western one.
Does my rising sign change in sidereal astrology?
Often, yes. The Ascendant shifts by the same 24 degrees or so, so if your tropical rising sign is in its first 24 degrees, your sidereal rising sign is the previous sign.
Which zodiac should I use?
Use the one whose tradition you're reading in. Western horoscopes, including ours, are written for the tropical zodiac; Vedic readings use the sidereal. Some people keep both charts and compare.
