What dates does the Sun spend in Gemini?

Roughly May 21 to June 20. These are tropical-zodiac dates, measured from the equinox rather than from the constellation of the same name, and the exact ingress moves by up to a day or so between years because the tropical year is not a whole number of days. If a birth falls within a day of either boundary, the sign has to be computed for that specific date and time - a fixed date table will get some of those cases wrong.

Which planet rules Gemini?

Mercury, in both the classical and the modern scheme. Gemini is one of the signs whose rulership was never reassigned after the outer planets were found, so traditional and modern sources agree here.

What does it mean that Gemini is a mutable air sign?

Gemini belongs to the air triplicity, described as hot and moist, which it shares with Libra and Aquarius. Mutable signs close a season and hand over to the next. The pairing of one element with one modality is unique to each sign - twelve signs, four elements, three modalities - so air plus mutable identifies Gemini and no other sign. Polarity is active, alternating around the zodiac so that every sign sits between its two opposites in polarity.

Which planets are strong or weak in Gemini?

Jupiter is in detriment here. Exaltation and fall are a fixed table inherited from Hellenistic astrology, not a judgment computed from the chart: they say a planet is easier or harder to work with in that sign regardless of anything else in the figure. Detriment is simply the sign opposite the one a planet rules. A planet with no listed dignity in Gemini is called peregrine, which means unaspected by dignity rather than weak.

What are the three decans of Gemini?

0 to 10 degrees is subruled by Gemini (Mercury); 10 to 20 degrees is subruled by Libra (Venus); 20 to 30 degrees is subruled by Aquarius (Uranus). This is the triplicity system, where a sign's three decans go to the three signs of its own element in zodiacal order, starting with itself. A competing Chaldean system assigns decan rulers by planetary order instead and produces different rulers for the same degrees, so a decan reading is only meaningful once you know which of the two systems it came from.

Gemini

05-21 - 06-20 · air · mutable · active

Dignities

Ruler: ☿ Mercury
Detriment: ♃ Jupiter
Symbol: Twins

Hellenistic tradition

Gemini is the diurnal domicile of Mercury. Mutable air, traditionally tied to exchange and pairing.

Modern Western reading

Modern Western astrology associates Gemini with communication, learning, and duality.

Same element

Decans

Planets in Gemini

Compatibility with all signs

All Gemini compatibility detail →

Questions

What dates does the Sun spend in Gemini?: Roughly May 21 to June 20. These are tropical-zodiac dates, measured from the equinox rather than from the constellation of the same name, and the exact ingress moves by up to a day or so between years because the tropical year is not a whole number of days. If a birth falls within a day of either boundary, the sign has to be computed for that specific date and time - a fixed date table will get some of those cases wrong.
Which planet rules Gemini?: Mercury, in both the classical and the modern scheme. Gemini is one of the signs whose rulership was never reassigned after the outer planets were found, so traditional and modern sources agree here.
What does it mean that Gemini is a mutable air sign?: Gemini belongs to the air triplicity, described as hot and moist, which it shares with Libra and Aquarius. Mutable signs close a season and hand over to the next. The pairing of one element with one modality is unique to each sign - twelve signs, four elements, three modalities - so air plus mutable identifies Gemini and no other sign. Polarity is active, alternating around the zodiac so that every sign sits between its two opposites in polarity.
Which planets are strong or weak in Gemini?: Jupiter is in detriment here. Exaltation and fall are a fixed table inherited from Hellenistic astrology, not a judgment computed from the chart: they say a planet is easier or harder to work with in that sign regardless of anything else in the figure. Detriment is simply the sign opposite the one a planet rules. A planet with no listed dignity in Gemini is called peregrine, which means unaspected by dignity rather than weak.
What are the three decans of Gemini?: 0 to 10 degrees is subruled by Gemini (Mercury); 10 to 20 degrees is subruled by Libra (Venus); 20 to 30 degrees is subruled by Aquarius (Uranus). This is the triplicity system, where a sign's three decans go to the three signs of its own element in zodiacal order, starting with itself. A competing Chaldean system assigns decan rulers by planetary order instead and produces different rulers for the same degrees, so a decan reading is only meaningful once you know which of the two systems it came from.

Reference, not advice

This is cultural and astronomical reference, not personal prediction or advice.

Tropical zodiac dates are astronomical conventions. Traditional interpretations are paraphrased from primary classical and modern sources. See sources and methodology.

Sources

Last reviewed 2026-05-28.