The Zodiac is a broad belt extending 9 degrees on either side of the ecliptic and known as Bhachakra or the Circle of Light. It is a circle which has no beginning or end.
In order to measure the distance, an arbitrary point is established, which is called the first point of Aries. The zodiac revolves once in a day on its axis, from east to west.
The Ecliptic is the path of the Sun which is known as Apamandala or Ravimarga in Sanskrit. It passes exactly through the centre of the zodiac longitudinally.
Zodiac Signs :
The ecliptic is divided into 12 equal compartments called the Signs of the Zodiac each being 30 degrees in extent. The commencement of Zodiac is reckoned from the first point of Aries. Each degree is divided into 60 minutes and each minute is further subdivided into 60 seconds so that the total extent of the zodiac is 21,600 minutes.
The ecliptic is marked by 27 constellations or Nakshatras often called Lunar mansions. This is because the Moon is brought into special connection with them as traversing 27 constellations and making a complete round of the ecliptic in a lunar month. Each constellation contains 4 padas or quarters and each quarter is equal to 3 1/3 degree of the celestial arc (rekha). The whole zodiac consists of 108 padas so that each constellation measures 13 degrees 20 minutes of arc.