According to astrology, zodiac signs are platonically or romantically compatible based on their sun, moon and love signs. Each of the 12 zodiac signs belongs to one of four elements, with some elements viewed as being more compatible than others.
In astrology, signs that have harmonious elements, such as water and earth, are more compatible. An example of elements that have a more challenging relationship with each other is water and fire. The three zodiac signs that fall under the water element are Cancer, Scorpio and Pisces. Those that belong to the air element are Gemini, Libra and Aquarius. Aries, Leo and Sagittarius belong to the element of fire, and Taurus, Virgo and Capricorn fall under the earth element.
People whose sun or moon signs fall under the same element are purported to be more suited to each other. A person's sun sign is denoted by the position of the sun during his time of birth. For example, according to astrology, a person with Cancer as his sun or moon sign can build good relationships with people whose sun sign is Scorpio or Pisces, since all of those signs fall under the water element. Having a moon sign in the same constellation as another person's sun sign also indicates the ability to get along well. For instance, a person with a moon in Libra is supposed to relate well with those who have a sun in Libra.
Love sign compatibility takes a deeper look into the connection between the planet Venus and other planets in an person's natal chart. Creating a natal chart identifies which sign Venus was in at the time of a person's birth. Love sign compatibility is also based on the compatibility of various elements.