We can calculate the Rashi of a person by seeing the Nakshatra of the person and its part. If a person is born in Mesha Rashi,his nakshatra should be between Ashwini to krittika 1st part nakshatra.From 2nd part of krittika nakshatra to 1st part of Mrigashirsha nakshatra born people have vrishabh rashi and so on.Each zodiac in our birth chart is of 30 degree and a nakshatra consists of 13 degree 20 minutes.It has four parts and each part is therefore 3 degree 20 minutes.Moon is Exalted in vrishabh(Taurus) and Debillited in vrishchika(Scorpio).Many detailed prediction of our life can be made based on nakshatra and Dasha system.