Reference : History of Astronomy in India. Indian National Science Academy.1985. Chapter 9. Indian Calendar from Post-Vedic period to AD 1900. Page 274: S.K. Chatterjee and A.K. Chakravarthy.
What is the ecliptic?
The ecliptic is the apparent yearly path of the Sun seen from the earth on the background of the stars.
What is the zodiac or rasi chakra?
The moon and planets are found within a belt of width eight degrees on either side of the ecliptic. This belt is known as the rasi chakra, or the zodiac. ( See : Measuring distances in degrees in the sky using your hand)
What is a nakshatra?
To indicate day to day position of the moon in relation to the stars, the zodiac has been divided into 27 equal parts, from a fixed initial point in the ecliptic. Each part is known as a nakshatra or nakshatra division. and it covers 13 deg 20 min or 800 min of arc of the ecliptic.
Each Nakshatra division is named after a selected star which is generally prominent or traditionally well known and is broadly equally spaced in the zodiac. These identifying stars are called yogataras.
Not all Yogataras are located in the lune of the nakshatra division. for eg Ardra, Swati, Jyesta, Poorvashada, Uttarashada, Sravana and Dhanishta.
The word Nakshatra in the context of panchangas means the nakshatra division signified by that Nakshatra.
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