Dasha (Periods): From Wikipedia:
“The Sanskrit term “Dasha” in Hindu astrology is used to indicate planetary periods. The planetary periods indicate when the good or bad effects are produced according to their placement by sign (Rasi), house (Bhava), combinations (Yogas or Raja Yogas) or aspects (Drishti). The Dasha Paddhati (system) of Directional Astrology is unique to the Hindus; it is found nowhere else. There are many kinds of Dasha systems, Parashara mentions forty-two of them, but of these only two are in vogue, namely, “Vimshottari” and “Ashtottari”. Dashas provide a system to judge the effects of the planets throughout a person’s life, by indicating how the planets distribute their effects. Each dasha is controlled by one of the nine planets, and the quality and relative benevolence of each period is determined by the condition and position of that planet in the natal chart. There are nine planets or grahas which severally rule the nine dashas: the seven classical planets, plus the north node, Rahu, and south node, Ketu, of the Moon.
There are at least 43 different dasha systems. “Dasha” is the major period of a planet. It is called the “Poorna Dasha” if the planet is the most powerful or is in its sign of exaltation, which dasha gives health and wealth; the dasha of a powerless planet is called the “Rikta dasha”, “Rikta” means poor or devoid of any power. Varahamihira explains that the dasha of the planet occupying unfriendly sign and navamsa will produce Aristaphala i.e. undesirable or miserable results; the planet that has fallen from exaltation but is in friendly or exalted navamsa gives ordinary results, and the planet that is ascending from debilitation but is in debilitated or unfriendly navamsa, gives a worthless period.[3] The dasha period of a planet includes the 9 respective Apahara periods of all the nine planets. In all dashas, the nine planets do have Apaharas. At the beginning of every dasha, the first Apahara belongs to the lord of dasha himself. The Apahara is also called Anthardasa or bhukti. The Apahara period is calculated according to the length of the dasha period.”
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To reduce negative effect for the Dasha/Periods it’s recommended to perform Yagya related to involved negative planets or to chant mantras at least 1 mala (108) per day or more (5, 11 malas).
For example, for the Gu/Ch/Ke (Gu Maha Dasha/ Ch Antra Dasha/ Ke Pratya Antra Dashs) you should chant the following mantras:
- Guru (Jupiter): OM BRIM BRIHASPATAYE NAMAHA
- Chandra (Moon): OM SOM SOMAY NAMAHA
- Ketu: OM KEM KETAVE NAMAHA
Dasha Period Analysis Example:
From now till 5th February 2016 (Guru/ Chandra period): This is medium period. Let things continue as it is without any change. There is possibility of being worried, tense, unknown fear and Vata and Kaffa related problems. Avoid any major investments and big changes. You will make new friends and increase your social circle. This is favorable time for more spiritual development. Due to position of Chandra and Guru (6th and 12th house) it is necessary to be careful of people near to you and about your health. Performance of Yagya for Guru and Chandra from time to time is recommended for more positive support of nature and positive energy.
Additional information can be found here:
Jyotish — “Science of Light” (Vedic Astrology) 