What Is a Nakshatra?
The zodiac is divided into 27 equal parts of 13 degrees and 20 minutes, one for each Nakshatra. Each Nakshatra is further divided into four padas of 3 degrees and 20 minutes, which gives 108 padas. Twelve signs of nine padas each account for the same 108.
How Your Birth Nakshatra Is Determined
Your birth Nakshatra, or Janma Nakshatra, is found from the sidereal position of the Moon at your date, time and place of birth. The Moon crosses a Nakshatra in about a day, so birth time matters more here than it does for the Rashi.
Nakshatra Lords and Dashas
Each Nakshatra has a lord, and the nine lords repeat in the same order three times: Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn and Mercury. The lord of your birth Nakshatra decides which planetary period your Vimshottari Dasha sequence begins with.
Nakshatra and Rashi
Nakshatra and Rashi describe different layers of the chart. A Rashi covers 30 degrees and a Nakshatra covers 13 degrees and 20 minutes, so each Rashi contains parts of three Nakshatras.