What 'sidereal' and 'tropical' actually mean
Tropical comes from the Greek for 'turning': the tropical zodiac is anchored to the turning points of the seasons. Its 0° Aries is wherever the Sun stands at the March equinox, so the tropical signs are really a seasonal calendar. Sidereal comes from the Latin for 'star': the sidereal zodiac is anchored to the fixed stars, so 0° Aries stays at the same place among them.
Two thousand years ago the two anchors were close. Precession, the 26,000-year wobble of Earth's axis, moves the equinox backward through the stars at about 50 arcseconds a year, or 1° every 72 years. The accumulated gap is the ayanamsa. The Lahiri ayanamsa, used by the Indian national calendar and by default on this site, measures it at 24.2° in 2026.
Western astrology chose the seasonal frame; Vedic astrology (Jyotish) kept the stellar one. Nothing else about the planets differs: the same ephemeris, the same moment, one subtraction. The Vedic vs Western comparison covers what the two traditions then do differently with the positions.
Sidereal zodiac dates (Lahiri ayanamsa)
These are the Sun-sign date ranges for the 2020s, sidereal next to tropical. They were read off the same ephemeris engine that casts the charts on this site, scanning each day at 12:00 UTC.
| Sign | Sidereal dates (Vedic) | Tropical dates (Western) |
|---|---|---|
| Aries | Apr 14 – May 14 | Mar 21 – Apr 19 |
| Taurus | May 15 – Jun 14 | Apr 20 – May 20 |
| Gemini | Jun 15 – Jul 16 | May 21 – Jun 20 |
| Cancer | Jul 17 – Aug 16 | Jun 21 – Jul 22 |
| Leo | Aug 17 – Sep 16 | Jul 23 – Aug 22 |
| Virgo | Sep 17 – Oct 16 | Aug 23 – Sep 22 |
| Libra | Oct 17 – Nov 15 | Sep 23 – Oct 22 |
| Scorpio | Nov 16 – Dec 15 | Oct 23 – Nov 21 |
| Sagittarius | Dec 16 – Jan 13 | Nov 22 – Dec 21 |
| Capricorn | Jan 14 – Feb 12 | Dec 22 – Jan 19 |
| Aquarius | Feb 13 – Mar 14 | Jan 20 – Feb 18 |
| Pisces | Mar 15 – Apr 13 | Feb 19 – Mar 20 |
Note what the table does not say. It does not say your sidereal sign 'is' something; it says where the Sun usually sits on that date. Vedic astrology reads the Moon sign (Rashi) first anyway, and the Moon changes sign every 2.25 days, so no date table can give it. The Moon sign calculator does.
Which sign changes, and which stays
A 24° shift inside a 30° sign means roughly four people in five get a different sidereal Sun sign, always the previous one: tropical Virgo becomes sidereal Leo, tropical Scorpio becomes sidereal Libra. The one in five born in the last six days or so of a tropical sign keeps it. Born Apr 14 through Apr 19, you are an Aries in both zodiacs.
The shift applies to everything in the chart, not only the Sun. Your Moon sign and rising sign move back by the same 24°, and so does every planet. What stays exactly the same is every angle between planets, because the whole chart turns together. A Venus–Mars conjunction is a conjunction in both frames.
Why there are several ayanamsas, and what '13-sign true sidereal' means
Everyone agrees the zodiacs drift apart; astrologers disagree on exactly which star marks 0° Aries. Lahiri (the Indian government's choice, anchored on the star Spica at 0° Libra) is the most widely used in Jyotish. Raman is about 1.4° smaller, Fagan–Bradley about 0.9° larger, and KP sits close to Lahiri. The differences matter only when a planet sits within a degree or two of a sign boundary; the calculator here lets you switch between Lahiri, Raman, KP and Fagan in chart settings.
The '13-sign' or 'true sidereal' zodiac is a different idea altogether. It uses the constellations' actual, unequal boundaries as drawn by astronomers, which is how Ophiuchus appears and why its dates differ from any table above. Jyotish does not use it: Vedic signs are twelve equal 30° divisions of the sidereal circle, the same shape as the Western signs, only shifted.
Does sidereal change your Moon sign and rising sign too?
Yes, by the same rule. If your tropical Moon is at 10° Cancer, your sidereal Moon is at about 16° Gemini. The rising sign (Lagna) shifts the same way, which also moves every whole-sign house, so a planet in your Western 10th house may land in your Vedic 9th. This is the single biggest reason a Vedic chart looks unfamiliar to someone who knows their Western chart well.
One layer exists only in the sidereal frame: the birth star (Nakshatra), a 13°20′ segment of the sky the Moon occupied at your birth, one of 27. Nakshatras anchor the Vedic timing system, so the Nakshatra calculator is a natural next stop after you have your sidereal Moon.
Check your sidereal signs from your birth details
The chart card under the headline shows your sidereal Sun, Moon and rising sign to the degree, with the ayanamsa used printed alongside, so you can compare it with your tropical chart and see the 24° subtraction yourself. Without a birth time the Moon sign is still usually readable; the rising sign is left blank rather than guessed.
From there, the Vedic birth chart calculator lists every planet in sidereal sign and house, and you can ask the AI Jyotishi to read the chart with you; it calculates first, then interprets from classical Jyotish rules and lists which parts of the chart it checked. Software, not a human astrologer. Interpretation, not a prediction or professional advice.
FAQ
Sidereal vs tropical questions
Are sidereal signs more accurate?
Not in a way anyone can measure. Sidereal and tropical are two reference frames for the same sky, like two temperature scales. Each tradition built its interpretation on its own frame. The sidereal frame does match the actual star background, which is why Vedic astrology uses it; whether that makes its readings 'more accurate' is not a claim this site makes.
How do I know my sidereal zodiac sign?
Subtract about 24° from your tropical Sun position, or read the table above, remembering that boundary dates can shift by a day. For an exact answer, and for your sidereal Moon and rising sign, enter your birth date, time and place in the calculator on this page.
Which astrology chart is most accurate?
The positions in any chart are astronomy and can be checked against an ephemeris; what differs between charts is the frame (sidereal or tropical), the ayanamsa, the house system and the birth time. A chart that states all four, as the one on this page does, can be checked. 'Accurate' beyond that is a question about interpretation, not calculation.
Is sidereal the same as Vedic astrology?
Sidereal is the zodiac; Vedic astrology (Jyotish) is a tradition that uses it. Some Western astrologers also work sidereally, usually with the Fagan–Bradley ayanamsa, while keeping Western techniques. Vedic astrology adds Nakshatras, whole-sign houses, the lunar nodes and dated planetary periods on top of the sidereal frame.
Why do 13-sign 'true sidereal' dates differ from this table?
Because that system uses the unequal constellation boundaries drawn by astronomers, including Ophiuchus, instead of twelve equal 30° signs. The table above is the twelve-sign sidereal zodiac used in Jyotish with the Lahiri ayanamsa. The two are not interchangeable.
Why does the table say a boundary can shift by a day?
The Sun enters a sign at a specific hour, which falls on slightly different calendar dates from year to year and in different time zones. Over longer spans, precession moves each boundary about one day later every 72 years. The table is right for most birthdays in the 2020s; for a birthday on or next to a boundary, the calculator with your birth time is the reliable answer.