x) Astrology

What is the Difference between Sun Sign of Western system and the Lagna  of Hindu system ? -
Or why I am getting a different birth sign here ?

Lagna is not the Sun Sign or the Rising Sign of Western System.  

Western System

                                   Sun Sign  ( Explanation of  - The difference between the Sun Sign and the Lagna - Lagna is calculated in here and the reading is based on the Lagna). In Western System of Sun Sign, all the people born in one month belongs to the same sign. Every year approximately around 21 of March to 20 th April The Sun is moving in the Aries Constellation. So all the people born in that month belongs to the Sign of Aries.  If you were born in between those two dates then you are a Aries Born.  This is a rough system just to give some kind of a reading for people who does not know their time of birth. But for people who knows the time of birth, the rising sign or the Lagna is the better option.