If you were born May 21st are you a Gemini or a Taurus?

It depends on the year when you were born, as the date and time when the Sun leaves Taurus and enters Gemini varies each year. To find out if your Sun sign is Taurus or Gemini you will need to know your date of birth, place of birth and time of birth for your birth chart to be created. Any professional astrologer will be able to do this for you, but there are Astrology websites, mine included where you can create your own birth chart for free.