In western astrology, there are 12 signs standing for 12 periods of a year. Stars are divided into many regions of different sizes, each called a constellation. Connecting all bright stars in a constellation with imaginary lines, different images in the shape of animals and objects are formed. People named each constellation according to its shape. The International Astronomical Union divided the sky into 88 constellations with precise boundaries, making every star belonging to a particular constellation.
Seen from Earth, the sun moves slowly in the Celestial Sphere (an outward projection of stars on a sphere) and passes through constellations, forming a large circle for a year. This circle is called Ecliptic. The Ecliptic is divided into twelve equal portions (each equivalent to 30 degrees); each portion was named after the closest constellation. All these twelve portions were called Ecliptic Constellations, according to which western horoscope theories developed.
The astrologists divide a year is into 12 periods, during each period the sun being in a constellation area. So everyone has a corresponding zodiacal sign according to the period his / her birthday lies in. The 12 signs are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. People believe that different sun signs of the zodiac present different characteristics and talents.