get Zodiac sign from birthdate javascript

gistfile1.js

function getZodiacSign(day, month) {

      var zodiacSigns = {
        'capricorn':'capricorn',
        'aquarius':'aquarius',
        'pisces':'pisces',
        'aries':'aries',
        'taurus':'taurus',
        'gemini':'gemini',
        'cancer':'cancer',
        'leo':'leo',
        'virgo':'virgo',
        'libra':'libra',
        'scorpio':'scorpio',
        'sagittarius':'sagittarius'
      }

      if((month == 1 && day <= 20) || (month == 12 && day >=22)) {
        return zodiacSigns.capricorn;
      } else if ((month == 1 && day >= 21) || (month == 2 && day <= 18)) {
        return zodiacSigns.aquarius;
      } else if((month == 2 && day >= 19) || (month == 3 && day <= 20)) {
        return zodiacSigns.pisces;
      } else if((month == 3 && day >= 21) || (month == 4 && day <= 20)) {
        return zodiacSigns.aries;
      } else if((month == 4 && day >= 21) || (month == 5 && day <= 20)) {
        return zodiacSigns.taurus;
      } else if((month == 5 && day >= 21) || (month == 6 && day <= 20)) {
        return zodiacSigns.gemini;
      } else if((month == 6 && day >= 22) || (month == 7 && day <= 22)) {
        return zodiacSigns.cancer;
      } else if((month == 7 && day >= 23) || (month == 8 && day <= 23)) {
        return zodiacSigns.leo;
      } else if((month == 8 && day >= 24) || (month == 9 && day <= 23)) {
        return zodiacSigns.virgo;
      } else if((month == 9 && day >= 24) || (month == 10 && day <= 23)) {
        return zodiacSigns.libra;
      } else if((month == 10 && day >= 24) || (month == 11 && day <= 22)) {
        return zodiacSigns.scorpio;
      } else if((month == 11 && day >= 23) || (month == 12 && day <= 21)) {
        return zodiacSigns.sagittarius;
      }
    }