What is zodiac and signs?

Imagine a belt around the earth which is 18 degrees wide. Along the middle of the belt goes the ecliptic or path of the sun as seen from earth. This imaginary belt around the earth is called zodiac. It is inclined at an angle of 23 degrees 28 seconds to the plane of the equator. Since the zodiacal belt forms a complete circle around the earth it is 360 degrees in total. This zodiac is divided into twelve equal parts called signs or rashi and each rashi spans 30 degrees.

The nakshatra constellation Ashwani is the starting point of the zodiac of the zodiac which is 0 degree and this is also starting point of first sign/rashi Aries/Mesha. Thus there are twelve signs in the zodiac. Ashwani is not a single star and there may be billions of stars in that range of 0-30 degrees of zodiac. In other words 1/27 of the entire stars in the cosmos.

The division of zodiac into twelve signs is fundamental in vedic astrology and the birth chart is constructed by placing planets into the signs based on their longitudes at the birth of individual. For example the longitude of the Sun at the time of birth is 65 degrees, the sun will be allocated the sign Gemini/Mithuna. Since each sign spans 30 degrees in the zodiac and the sun has completed two signs Aries and Taurus (2x30=60). and now at 5 degrees into Gemini/Mithuna. Similarly other planets are placed in their respective signs.

Each sign is ruled by a planet. While the sun and moon own one sign each, the remaining planets own two signs each. Rahu and ketu are generally not allotted ownership of the signs. The following table illustrates names of twelve signs, their lordships, nature etc.