Gemini. Artwork of the zodiacal constellation Gemini, representing the twins. The outline of the constellation is shown by the purple lines linking the important stars. The zodiac is the band in the sky through which the Sun appears to move. The Sun is in Gemini roughly between the 21 May and 21 June each year. The constellation is prominent and bright, and is visible in Winter from the Northern Hemisphere. The celebrated stars of Castor (right) and Pollux (left) form the heads of the twins. North is at the top.