Yoga (Hindu astrology)
As per Jyotisa a Yoga is given rise to when one planet, sign or house is related to another of the same kind or different kind by way of placement, aspect or conjunction. It is the active consideration of planetary yogas and the active consideration of the planetary Dashas i.e. directional effects, which are the two most important factors that distinguish Hindu astrology from Western astrology.
New millennium astrological chart
Laghu Parashari is the concise version of the predictive side of the Hora Shastra, and the Parashari System is most widely followed, having stood the test of time and because it is simple and unambiguous. The ancient Hindu astrologers seem to have confined their exercises to the seven planets – the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn; Rahu and Ketu, these two that are mathematical points, are referred to but rarely. Parashara also refers to five more Chayagrahas which are all actually invisible mathematical solar positions but having impact on the life of individuals and nations. The Rigveda does refer to the total of thirty-four, comprising twenty-seven Nakshatra-divisions of the Zodiac and the seven planets which was the general format then in use. However, elsewhere it also refers to the total of forty-nine by adding to the said thirty-four the two Chayagrahas (the lunar nodes), the twelve rasis (signs) and the Ayanamsa. Varahamihira favoured Satyacharya’s Dasha system though he says many had spoiled it by useless multiplications but Satyacharya did not deviate from the basic Parashari principles. Because of there being nine active planets and equally active twelve signs (including their numerous sub-divisions) and twenty seven nakshatra divisions, yoga-formations are unavoidable.
All planets jointly and severally without any exception are the indicators of future events, they chart the course of fate. And, all good or bad yogas depend on planets and the good or bad results of planets depend on the good or bad yogas caused by those planets. All planets influence each other, and no planet can stay uninfluenced on account of all planets invariably establishing at all times Sambandhas i.e. mutual associations, directly or indirectly. Auspicious yogas arise when lords of kendras (squares) and trikonas (trines) i.e. the lords of auspicious bhavas (houses) establish a mutual association and inauspicious yogas, when lords of trika-bhavas (evil houses) or weak, afflicted cruel planets afflict the kendras, the trikonas and / or their lords, when bad to very bad results are experienced during the course of their respective dashas and antra-dashas.
In Hindu Astrology, the word, Yoga, that has been derived from the Sanskrit root, Yuj, meaning to join properly, to control judicially or to integrate, has been used to indicate the Soli-Lunar distances, and the planetary situations, associations and combinations. Yogas are formed when one planet, sign or house is related to another of the same kind or different kind by way of placement, aspect or conjunction. It is the active consideration of planetary yogas and the active consideration of the planetary Dashas i.e. directional effects, which are the two most important factors that distinguish Hora-shastra or Hindu astrology from Western astrology and lend support to the indigenous origin of the former system.
A yoga may be good or it may be bad in its effect. The good yogas are called the Shubha-yogas or simply yogas, the bad i.e. evil; yogas are called the Ashubha-yogas or simply avayogas or durayogas. Raja yogas indicate a high degree of power and authority, and the Dhana yogas, a greater degree of material possessions. Arishta yogas indicate difficulties in life, and the Daridra yogas indicate poverty. Parvarajya yogas or Sanyasa yogas that give religious merits compel a person to give up all wealth and material possessions to become a mendicant and beg for alms, these are not avayogas.
The so-called natural benefics and the so-called natural malefic are not always benefics or always malefic for all lagnas by virtue of their bhava-lordship. By virtue of their owning auspicious or inauspicious bhavas they are termed Shubha or Papa; even Papas can confer good results. There are Arishtayogabhanga yogas that cancel out the bad effects of Arishta yogas, and there are also Rajayogabhanga yogas that nullify Raja yoga effects. The Sun situated at the end of Pisces, when it will also be in Vargottamamsa; the Moon situated at the end of Aries, when it will be in Sagittarius navamsa; Mars in Sagittarius; Mercury in Leo; Jupiter in Gemini; Venus in Aquarius and Saturn situated in Virgo sign are called Ucchabhilashi (desiring to go to a higher place). The Ucchabhilashi planets, like the planets occupying their own or exaltation signs, generally give yoga results (benefic results), they tend to confer Royal honours and make one hold the foremost place in the family and own circle of activity. 
Role played by yogas and yoga-causing planets
Astrology fearlessly ventures into the Unknown seeking that which can be effort fully known because in Astrology intuition does not play any role. It is based on the inferences drawn after the mathematical application of the approved laws and the various distinct significators. Each Nakshatra (Constellation), each rasi (Astrological sign) and each Graha (planet) is a vibrant creative significator whose significance has to be methodically ascertained and judged. According to the Hindu Astrology all planetary combinations and their indications are based on the strength, nature, aspect, avastha (status) and combination of planets, on the qualities and the strength of the rasis and bhavas owned, occupied and aspected by planets, and on the influence of the yogas given rise to by planets which factors are required to be taken into account collectively. Thus, Hindu Astrology basically requires the discerning eye to be able to identify the yogas and then judicially apply the prescribed results in accordance with the established principles. All standard yoga-formations are duly named and their results, prescribed.
All yogas are based on certain fundamental principles, these stand described in all standard texts but not all texts cover the description of all known widely recognised possible planetary combinations and associations. Of course, there are a few instances where the texts do offer differing constitution and interpretation of one and the same named yoga. Gajakesari yoga comes into being when Jupiter is situated in a kendra (in square-position) from the Moon but according to one school this yoga will arise only when Jupiter and the bright-half Moon are in mutual 10th and 4th position in Pisces, Taurus, Sagittarius and Aquarius. Yet another text tells us that the Moon and Jupiter in mutual kendras will not give rise to the Gajakesari yoga if either the Moon occupies Scorpio or Mercury happens to be in the 5th house from the Moon or only if the Moon and Jupiter combine in Cancer or in Capricorn even if Jupiter in the latter sign is combust. In such rare instances, experience alone counts. Moreover, there are certain yogas described in the texts which simply cannot occur, these relate to Mercury and Venus vis-à-vis the Sun; Mercury never goes beyond 28 degrees either in front or behind the Sun and Venus not beyond 47 degrees, and Mercury and Venus cannot remain apart from each other more than 61 degrees arc-distance. Saraswati yoga given rise to by the three natural benefic planets, namely, Mercury, Venus and Jupiter co-operating with each other is an auspicious yoga which is not rare in occurrence but when its participants are not strong merges with other yogas. 
Impact of yogas
Even though classification and grouping of yogas is a difficult task, generally the yogas are known as Chandra yogas, Surya yogas, Panch Mahapurusha yogas, Nabhas yogas, Raja yogas, Dhana yogas, Arishta yogas, Daridra yogas, Reka yogas, Parvarajya yogas, and so forth, but the common factor to be reckoned with in case of all these yogas is the relative residential strength of the planets and of the bhavas (houses) involved whether by ownership or by occupation or by aspect.Janardan Harji in the Fourth Chapter of his Mansagari, which is devoted to yoga-formation and their results, tells us that if at birth all planets combine in the 7th house from the lagna then one becomes fortunate in the 30th year of life onwards and enjoys exceptional yoga-results; if the Moon occupies a kendrasthana and the Sun simultaneously happens to occupy a trikonabhava then the person even though lowly-born will rise to be a king, and that if three planets simultaneously happen to occupy their own signs then one rises to be a royal minister, if three planets simultaneously happen to occupy their respective signs of exaltation one becomes a king, if three planets similarly happen to occupy their respective signs of debilitation the person even if highly-born will become a menial and if three planets are simultaneously combust the person will be a fool.
The lagna (ascendant) and the Chandra-lagna (natal Moon-sign) gain strength by being aspected by a planet, preferably by their own lords; when their respective lords are strongly placed forming auspicious yogas then good results are to be anticipated failing which all auspicious yogas become defunct. If at the time of birth the lagna or the Moon is not aspected by any planet the results of Raja yogas do not fructify. Malefic planets should certainly not afflict the lagna, the Moon, the yoga-causing planets and the bhavas involved; whichever bhava as is associated with or aspected by either their respective lords or by benefic planets gains vitality, the good effects are destroyed if malefic planets aspect or join them. The effect of an aspect is equal to that of conjunction and in practice found to be more effective. The Sun and Jupiter are the karakas (significators) of the 10th house, any kind of sambandha (mutual association) established by these two makes one adept and shine in his/her chosen field of creative/scientific/religious/philosophical activity, become a high ranking official or advisor and famous. Jupiter situated in the Karakamsa i.e. in conjunction with the Atmakaraka in the Navamsa-chart makes one master the Vedas or become a philosopher or a religious leader; Venus likewise situated makes one a great political figure. 
The yoga-results are indicated by the circumstances in which the birth has taken place and the particular course followed by one’s life from birth to death. But, yogas are of no avail if the yoga-giving dashas do not run their course in the life of persons standing to gain; yoga-causing planets give their results during the course of their dashas and antra-dashas. The dasha of a malefic planet will produce bad results and the antra-dasha of a malefic in the dasa of another malefic will produce evil results. Saravali declares that if the period of a cruel planet has the antra-dasha of another malefic, the person suffers death. Therefore, it is imperative that the status of the lords of the nakshatras occupied by planets, in particular that of the Moon, and by the rising-point of the lagna is properly determined. The Sun onwards all planets do not in the course of their dasha and antra-dasha confer results in accordance to the bhava formed by their rasis as counted from the lagna alone but according to their particular associations. Planets tend to give results of the lords of the nakshatras occupied by them; benefic nakshatras become afflicted if they are occupied by Papa grahas. The Sun and the Moon afflicted by Rahu or Ketu spoil the good effects of other yogas.
Many learned in Hindu Astrology have attempted to enumerate the exact number of possible yogas and avayogas. Varahamihira has listed 16 Raja yogas if Mars, Saturn, Sun and Jupiter or any three of them exalted and one of these three occupies the lagna and forty four Raja yogas if lagna or Chandra-lagna occupies Vargottama and has the aspects of four more planets excepting the Moon but which if read with St. 14 of Ch. I of Brihat Jataka actually works out to 264 yogas and 528 combinations for royalty both from lagna and Chandra-lagna. Later on at the very beginning of Chapter XII of the same text he tells us that the Yavanas had described 1800 varieties of Nabhas yogas. Mantreswara in merely three verses has described 66 yogas including 28 Mahayogas.
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