GEMINI, GEMINIS, the constellation the Twins, is generally portrayed as Castor and Pollux, but also sometimes as a male and a female. The constellation lies in the northern hemisphere, partly in the Milky Way, near Orion. In the time of Hipparchus each constellation stood next to the sign bearing its name, but by Chaucer's time the constellation lay two-thirds into the sign bearing its name. Gemini, as a whole, produces an equable temperature (Tetrabiblos II.11); the foreparts of Gemini cause slenderness and the hindparts robustness (Tetrabiblos III.11). It is the night house of Mercury (Tetrabiblos I.17). The Twins are generally painted naked, wrestling with each other (Confessio Amantis VII.1031-1050).

The sun is in Gemini, a little from its declination or highest point, reached on June 13 in Chaucer's time, when May meets Damian in the pear tree, MerchT 2222. Venus flees to Cilenios's tower, that is, to Gemini, the night house of Mercury, Mars 113-114. Gemini is the third sign of the zodiac, Astr I.8.3. A man born under Gemini will have thin arms and armholes, Astr I.21.74-75. Gemini is the nadir (exactly opposite) of Sagittarius, Astr II.6.16. All the signs from the head or beginning of Capricorn to the end of Gemini rise above the horizon in less than two hours and are called tortuous, crooked, or oblique signs, Astr II.28.22-30. Gemini, an eastern sign, obeys Cancer, a western or "sovereign" sign, Astr II.28. 36. [Cilenios: Damyan: Januarie: May]

Gemini, Latin nominative plural, appears four times in the Astrolabe; Geminis, Latin dative plural, appears medially, MerchT 2222, and three times in the Astrolabe.