In astrology , Gemini is the third sign of the zodiac , considered as governing the period from about M ay 21 to about June 21. It is represented by a set of twins (or in Egyptian astrology by a pair of goats and in Arabian astrology by a pair of peacocks). In addition to their identification as Castor and Pollux , the twins have also been related to other celebrated pairs, such as the younger and older Horus or Romulus and Remus .