You need to know about "house" :

Why constellation 30 ° partitions are equal?And it has personal house small?

Solve this question often hear, here.Palace are size and element partition not, because of the zodiac is a virtual zone, a virtual perfect circle, so, also can be divided into 12 points perfectly.That is why astrology so pay attention to the symbols in the symbolism and meaning of digital, because from the beginning to the end, including the ecliptic itself is an imaginary symbolic perfect circle in the brain.And relatively zodiac, the earth is not a perfect sphere, while personal house was born according to the geographical location to delimit the local meridian.At the same time as the method of calculating palace, people have different definition of "circle", such as the Placidus, Campanus, Regiomontanus, Koch palace method, such as some symbolically equal to 12 palace, while others will be small.(The constellations /astro/zhishi/)