Signs and constellations

How to use it

With a birth chart saved on this device the wheel opens on your birth; without one it shows the sky at this minute, and the two buttons switch between them. Pick any of the ten bodies from the row of glyphs and a gold pointer runs out through all three rings, with its three answers written in the middle: the tropical degree, the sidereal degree and the constellation. The list below gives all ten at once, and the drift section gives today’s ayanamsa, today’s Sun three ways, and roughly the year the March equinox point crosses from Pisces into Aquarius by the official boundaries.

Reading the answers, with an example

Take the Sun at 10° Taurus in the tropical zodiac. The ayanamsa in recent decades has been about twenty-four degrees, so the sidereal Sun is twenty-four degrees further back, at 16° Aries. Along the ecliptic the constellation Aries covers roughly 29° to 53° of longitude, and 10° Taurus is 40°, so the Sun also stands in front of Aries. As a rule of thumb, a planet in the last six degrees of a tropical sign keeps the same sign sidereally, and anything earlier in the sign moves back one. The constellation always needs the look-up, because its borders are uneven.

Why there are three answers

The tropical zodiac is tied to the seasons. It starts at the point where the Sun crosses the equator in March and divides the year into twelve equal parts of thirty degrees, whatever stars happen to lie behind them. Two thousand years ago the signs and the constellations of the same names lined up. The Earth’s axis wobbles slowly, like a top, and carries the starting point backwards against the stars by about a degree every seventy-two years, so they no longer do.

The sidereal zodiac, used in Indian astrology, keeps the signs fixed to the stars instead and subtracts that drift, the ayanamsa. There is more than one way to set it; this page uses Lahiri’s, the Indian government standard, and is within a few minutes of arc of the published tables.

Ophiuchus is not a lost sign

The constellations are the areas of sky the International Astronomical Union drew borders round in 1930, and they are not equal. Along the path of the Sun, Virgo is more than forty degrees wide and Scorpius less than seven, and a thirteenth, Ophiuchus, the serpent bearer, sits between Scorpius and Sagittarius for eighteen days of the Sun’s year. None of that changes the signs, which were never measured from the constellations in the first place. Because planets wander a little north and south of the Sun’s path, they can also stand in constellations off it altogether, and the table above names whichever one it really was.

Common confusions

The story that astronomers have changed the zodiac comes round every few years. Nothing changed: astronomy has always said the Sun passes through thirteen constellations of unequal width, and astrology has always said the tropical signs follow the seasons. The two statements answer different questions.

Sidereal astrology is not the same thing as the constellations either. It keeps twelve equal signs of thirty degrees and only anchors them to the stars, so a sidereal sign and the constellation of the same name can still disagree by several degrees where the constellation is wide or narrow. Sidereal traditions also set the ayanamsa slightly differently, which can move a placement by a degree or so.

Your chart in the sidereal zodiac, drawn the Indian way, is on Vedic chart, and the lunar mansion of your Moon on Nakshatra. The twelve tropical signs are described on The signs, the bright stars along the zodiac on Fixed stars, and the equinox the tropical zodiac is counted from on The year.

What this page claims

The positions are worked out on this device, the constellation for each planet is looked up from the official boundaries, and the three answers are set side by side. Which zodiac to use is a choice each tradition has made; the page does not make it for you and predicts nothing.