If we go back a 1000 years, we learn that Bharat had Gurukuls (school) where the Guru would teach his Shihyas (Students) the way of life. Guru in Sanskrit means dispeller of darkness (Gu – darkness; Ru- light). He would remove “the darkness” meaning create awareness about various situations that life could present to them and provide guidance to tread on the right path.
Even before Westerners started celebrating Teachers day, we Indians, astrological devoted a day to our Guru’s. Every year, on the Ashadha Purnima, bright lunar full moon, when the student is the most enlightened, he would pay respects to his Guru for being his guiding light. Ved Vyas, the author of The Vedas, Puranas, and Mahabharat, who bestowed us with abundant knowledge, is said to be born on Ashadha Purnima. That is why this day is also called Vyas Purnima.
If we relate it to the planets, Jupiter or Brihaspati is the Guru of the Devta’s. And so people ruled by number 3 in their date of birth or name, possess qualities of Knowledge, Guidance, and Justice.