You know you're a Gemini. Do you know which Gemini you are?

What is a Gemini really like?

Gemini is the third sign of the zodiac: an air sign, a mutable sign, ruled by Mercury. The Sun is in Gemini from May 21 or 22 to June 20 or 21. What any one Gemini is really like depends on the rest of the chart: the Moon, the rising sign, Venus and Mars.

Gemini is one of twelve. What is the zodiac, and where did the twelve signs come from?

What it is

Your sun sign is the slice of the zodiac the Sun was standing in on your birthday. The zodiac here is a measuring tape, not a picture: the Sun's yearly path cut into twelve equal slices of 30°, counted from the spring equinox. Gemini is the third slice, and the Sun crosses it from May 21 to June 21. ¹

It isn't the constellation. When the Babylonians matched twelve star patterns to twelve equal slices, the dates and the stars lined up. Earth's axis has wobbled since, so on the same dates the Sun now stands in front of different stars, and astronomers count thirteen constellations on its path, not twelve. Western astrology keeps its slices tied to the seasons, not to the stars. ¹

Gemini is a air sign and a mutable sign. Ptolemy grouped the signs in triangles of three, 120° apart; Gemini's triangle is Gemini, Libra and Aquarius, the one later astrologers called air. The modes come from the seasons: mutable signs fall in the last month of a season, when it is already changing. ²

A ruling planet is the planet a sign is said to belong to, its "house" in Ptolemy's word. Tradition gives Gemini to Mercury. ²

A sun sign is one placement out of many. The Moon, the rising sign and every planet sit in signs of their own, which is why two people with the same sun sign can seem to have very little in common.

This is the short version for one sign. How the zodiac was built, and its whole history, is on the master page: What is the zodiac, and where did the twelve signs come from?

Gemini in the old books

The traditional portrait of the sign, the same for everyone born under it.

Gemini, in the old books, belongs to Mercury, the messenger, and is one of Ptolemy's bicorporeal signs, the double-bodied ones that sit at the end of a season and borrow from both sides of it. The portrait follows: quick, curious, sociable, a talker who can hold two opinions at once and enjoy both. ²

The old writers' worry is that a Gemini gets bored. Restless, changeable, said to start three books and finish the one nobody recommended. The mutable mode, the books say, is the part that adapts, and Gemini adapts to the room it's in, which can look like charm one day and like two different people the next.

That's the Sun sign alone, the same for every Gemini born since the Babylonians. A steady earth Moon in the chart changes the picture more than you'd think.

Where Gemini comes from

Era by era, with sources. More in the Reading Room.

Ancientc. 1000–450 BCEBabylonian astronomers built the zodiac out of eighteen reference star groups over about a thousand years; by around 450 BCE it had settled into twelve equal zones along the path of the Moon and planets. ³
Ancient419 BCEA Babylonian text dated 419 BCE is the first to list all twelve zodiac signs, and the Twins are among them. Late Babylonian astronomical texts call the sign Māšu. ^4,5
Ancient410 BCEThe earliest known horoscopes, from Babylon and Nippur, date to this year. ³
ClassicalRoman eraPseudo-Hyginus (2.22) says many astronomers took these stars for Castor and Pollux, the most devoted of brothers, set in the sky by Jupiter for their loyalty. He records other pairs too: Hercules and Apollo, or Triptolemus and Iasion. ⁶
Classical2nd century CEPtolemy, working in Alexandria, writes the Tetrabiblos. It gives each sign a ruling planet, groups the signs in triangles of three and sets out the angles between signs that astrologers still use. ^7,2
Classical2nd century CEPtolemy makes Gemini one of the four bicorporeal signs and a house of Mercury. His map of the world gives it Hyrcania, Armenia and Matiana, with Lower Egypt and Cyrenaica nearer the centre. ^2,8
Medieval12th centuryThe Persian astrologer Abu Ma'shar (died 886) is read in Latin across Europe; the University of Edinburgh holds a 12th-century Latin copy of his introduction to astrology. ⁹
Medievalc. 1390sChaucer dates a scene in the Merchant's Tale by the Sun: it was in Gemini, he guesses, not far from Cancer. ¹⁰
Medievalc. 1464In the zodiac man of an English doctor's folding almanac (Morgan Library), Gemini governs the arms: the twins, a pair of them. ¹¹
1800s1890The first number of Alan Leo's Astrologer's Magazine goes on sale in July 1890. Annual subscribers get a free horoscope with a short reading: astrology by post, for ordinary readers. ¹²
1910s1917Alan Leo is fined for fortune-telling at the Mansion House on 16 July 1917. He dies that August, working on a system of astrology without predictions. ¹²
1930s1930–1937R. H. Naylor's horoscope for the newborn Princess Margaret runs in the Sunday Express on 24 August 1930 and becomes a regular column. By 1937 it is organised by the twelve sun signs, and newspapers on both sides of the Atlantic follow. ¹³
1960s1968Linda Goodman's Sun Signs is published: a whole book built on the twelve sun signs. ¹⁴
1980s–90s1980–1999Computers take over the arithmetic. Astrodienst in Zürich, whose founder had been writing astrology software since 1979, starts selling colour birth charts in 1980, goes online in 1996 and adds free daily horoscopes in 1999. ¹⁵
2010s2016NASA publishes a short explainer: the Sun crosses thirteen constellations, the Babylonians picked twelve to fit a twelve-month calendar, and "we didn’t change any zodiac signs". ¹
Today2024A Pew Research Center survey finds that 30% of US adults consult astrology, tarot or a fortune teller at least once a year, mostly for fun, with whole astrology cultures on TikTok and other platforms. ¹⁶

Worked out, not guessed

Calculated facts only, worked out the same way the machine does it.

Venus never gets more than about 47° from the Sun, so a Gemini's Venus is always in one of five signs: Aries, Taurus, Gemini, Cancer or Leo.
The Moon changes sign every two and a half days. Without a birth time and place, most birthdays could belong to either of two Moon signs. (91.1% of birthdays from 1950 to 2029, once every time zone on Earth is allowed for.)

Every Gemini reads this page. Only your card knows you.

Your card is worked out from the day, the minute and the place you were born: your birth chart, your love chart, your numbers and the sky you arrived under. This is what it covers.