Hindu System's 27 Nakshatras

Nakshatra OR Constellations

It was observed by the ancient Astronomers that many changes occurred within the 30 degree zones mapped out by the Zodiac. It was therefore, found necessary to subdivide each of the twelve sections or Signs of the Zodiac. Using the belt of Fixed Stars which encircle the Earth at the Equator as markers, they divided the Zodiacal Background into 27 sections, the boundary of each being marked by a particular Fixed Star, located close to the Zodiacal belt. These sections are known as the Asterisms or Nakshatras. 
They begin at the same point in the Constellation Aries which marks the beginning of the Zodiac,. and since each extends over an arc of 13deg-20', there are therefore twenty-seven of them in the complete circle of 360 degrees.

The 27 'Nakshatras' in the Hindu System of Astrology :

The Zodiac, therefore, divides heavens into twelve equal sections of thirty degrees each. The Asterisms, however, are sections or divisions of the heavens of 13deg-20' each. But it was found that changes in conditions and characteristics occurred even within these smaller boundaries and so each Asterism is further subdivided into arcs of 3deg-20' or into quarter sections.