Some astrologers believe that if any one of Sun or Moon is afflicted by Rahu or Ketu in a horoscope by means of an aspect from such Rahu or Ketu, a grahan yog or yoga is formed in the horoscope, in this case also. Combining these definitions, it can be said that if Sun or Moon is either placed with any one of Rahu and Ketu or if Sun or Moon receives an aspect from Rahu or Ketu, a grahan yog or yoga is formed in the horoscope. The literal meaning of grahan is to eat up completely and it is believed that Rahu or Ketu eat up Sun and Moon completely if this yog is formed in a horoscope which means that Rahu or Ketu destroy the significances of Sun or Moon in a horoscope if grahan yog is formed in the horoscope.
Let’s now try and analyze this definition with the help of scientific analysis and statistics. As we know that there are only 12 houses in a horoscope and accordingly all the planets among navagraha are placed in one or the other house among these 12 houses of a horoscope. Rahu and Ketu always move in retrograde motion according to vedic jyotish and their duration of stay in one zodiac sign is about 18 months. Sun completes its transit in one sign, in about a month and Moon completes its transit in one sign in about 2 and a half days. Let’s assume that Rahu is placed in the sign of Scorpio and Ketu is placed in the sign of Taurus and as we already know, both these planets are supposed to spend 18 months in this sign and hence their placement can be taken as a long duration placement compared to the transits of the Sun and Moon. Now during these 18 months, whenever the Sun transits through Scorpio or Taurus, a grahan yog or yoga is formed in the horoscope as Sun will be placed with Rahu or Ketu in the horoscope. This means that every 6th horoscope or person will be having a grahan yog or yoga in his horoscope as there are only 12 houses in a horoscope and the chances of Sun being present in 2 specific houses out of these 12 houses are one in every sixth horoscope. Looking at the statistics provided by the extended definition of grahan yog or yoga which says that even an aspect from Rahu or Ketu on Sun can form a grahan yog or yoga in the horoscope, at least 50% of the horoscopes will be having a grahan yog or yoga either due to placement relation or due to aspect relation of Sun with Rahu or Ketu. Similarly, the same percentage of horoscopes will be having a grahan yog or yoga due to the relation of Moon with Rahu or Ketu on the basis of placement or aspect. Combining these factors, about 70-75% of the horoscopes are having a grahan yog or yoga which means that almost every horoscope in the world and every person of the world is having a grahan yog or yoga in his horoscope and accordingly all of these people should suffer from the bad effects of grahan yog or yoga.
These figures are too high to be practical and hence they are not practical because something which is happening to every person of the world is routine and not a yoga and a yoga on the contrary is something that is happening only to a few people. Hence, grahan yog or yoga is not formed only according to the conditions mentioned in the prevalent definition of this yog and more conditions should be met in a horoscope in order for the formation of grahan yog or yoga in a horoscope. The nature of the planets involving in such combination is the foremost and the most important aspect that should be checked in order to determine the formation of grahan yog or yoga in a horoscope. For example, in case of a Sun-Rahu combination in a horoscope, there are four possible combinations that can be formed which are, Benefic Sun with benefic Rahu, Malefic Sun with benefic Rahu, benefic Sun with malefic Rahu and malefic Sun with malefic Rahu and out of these four combinations, only the last two combinations can form a grahan yog in the horoscope as the combinations with a benefic Rahu will not form a grahan yog or yoga because benefic planets do not make negative yogas in horoscopes. Further, for the last two combinations, the strength of Sun and Rahu is checked in a horoscope, the overall strength of so formed grahan yog is checked, the influence of other good and bad planets on Sun and Rahu is checked, the presence of other good or bad yogas in the horoscope is checked and many other aspects are checked in a horoscope before predicting the formation, strength, field of impact and time of impact of a grahan yog or grahan yoga in the horoscope which is formed due to the combination of Sun and Rahu in a horoscope. These calculations are done in a similar way in case of Sun Ketu combination, Moon Rahu combination and Moon Ketu combination and then a final decision is taken regarding the formation of grahan yog or yoga in a horoscope.
In my observation, I have seen that in many cases of apparent grahan yog or yoga, this yog is either not formed at all in the horoscope or it is not strong enough to do significant damage, as the formation of a defect in a horoscope cannot do significant damage if such a dosh or yog is weak or very weak. Hence all the possible and important aspects should be checked properly from a horoscope, before jumping to any conclusions about the presence of grahan yog or yoga in the horoscope. It should also be noted here that the some combinations of Sun or Moon with Rahu or Ketu can form very beneficial yogas or benefic influences in the horoscope and accordingly the natives under the strong influence of these combinations are likely to benefit from them instead of suffering from them. For example, the combination of a benefic Sun and a benefic Ketu in a horoscope can give very good results to the native regarding power, authority, deep insight, intelligence, management skills, inheritance, continuation of family through healthy and capable male children and many other things and accordingly the natives under the strong influence of a benefic Sun Ketu conjunction or combination in a horoscope can come across some of the above mentioned benefic results depending upon their overall horoscopes. Similarly, the presence of a benefic Moon with benefic Rahu in a horoscope can form a benefic yoga called Shakti yog or yoga in the horoscope which can bless the native with very good progress in the fields of spiritualism and paranormal, very good positions of power with government or some private organizations, easy access to comforts and luxuries and many more things depending upon the horoscope of the native and accordingly the natives having a benefic Moon Rahu conjunction or Shakti Yoga in their horoscopes can witness the results which are quite opposite to the results indicated by grahan yog or yoga. The reason for such good results in many of such combinations of Sun or Moon with Rahu or Ketu is that these combinations are formed by benefic Sun or Moon with benefic Rahu or Ketu and the combination or conjunction of two benefic planets is likely to give good and good results only and such combination is not likely to form malefic yogas like grahan yog or yoga in the horoscope.
Hence a grahan yog or yoga with good strength is actually formed in a very few horoscopes though it may be virtually present in every horoscope which means that it may be formed in every horoscope according to its prevalent definition whereas in actual practice a benefic combination of Sun or Moon with Rahu or Ketu like Shakti Yoga may be present in the horoscope which can bless the native with very good things depending upon the overall horoscope of the native.