Firdaria are a systerm of planetary periods similar to the Dasha system of Vedic or Indian astrology(Jyotish- science of light), that was introduced around 750 CE by the great Persian astrologer Abu Ma'shar.
The basis of this predictive method is that a particular planet becomes sensitized in one's birth chart for a number of years. Transits to or from the planet ruling the major period takes on more significance during the period in question.
If you were born with the Sun above the horizon(day), you begin your life in a Sun period.
And if you were born at night you start life in a Moon ruled period. Although there's some disagreement among astrologers regarding the order of the firdar periods for a night birth, the order employed by this Firdar calculator seems to work best according to my experience.
The Firdar, by Steven Birchfield
