While analyzing the effects of a dasha period it's very helpful to examine the transits at the time of the commencement of the mahadasha or sub period. I once asked K.N. Rao if this was an important step in dasha analysis. His answer was, "It is useful, and should be examined."
Rao's encouragement is, of course, based on what is written in the classic texts. For instance, sage Parashara says this in theBrihat Parashara Hora Shastra:
A planet placed in an auspicious bhava (house) like Trikona (trine) etc., at the commencement of the Dasha, produces favorable results in his Dasha. It is therefore, essential that the placement of a planet at the time of birth and at the commencement of the Dasha, should both be taken into account for the assessment of the Dasha effects.
- Brihat Parashara Hora Shastra, Ch. 48 v. 5-8 (translation R. Santhanam)
In the Saravali, sage Kalyana Varma says:
Planets in exaltation, own Rashi, own Navamsha, friendly sign, possessing full rays and those with full strength prove auspicious in their Dashas. At the commencement of a Dasha a planet that is strong, or is in a friendly division or is in aspect to a benefic will also yield similar good results.
- Saravali ch. 41 v. 6
Sage Varma later emphasizes looking at the aspects of planets by transits to the natal Moon:
Mercury's aspect to the Moon at the commencement of a Dasha, confers learning while the aspects of other planets will give effects according to their nature.
- Saravali ch. 41 v. 15
The following example chart is of a woman who has been experiencing depression over the past year, which is quite uncharacteristic for her. She has always been a professionally driven person and quite successful, however, now she's found that she's lost virtually all motivation.
She's in a Jupiter-Rahu dasha which began on November 28, 2005. Notice that, at the commencement of Rahu's sub period, Ketu was transiting right over her Moon and ascendant within just a few degrees. Furthermore, Saturn's 3rd house aspect from Cancer also aspects them as well. Ketu and Saturn are the two primary influences that can cause depression, especially when aspecting the Moon. They can represent lack of motivation, withdrawal, and loss especially when in combination.
Examining the transits at the commencement of the dasha or sub dasha can provide very helpful clues as to the results of the dasha. Of course, this is only one factor of many, and shouldn't be over emphasized. But sometimes, as in this case, it can help to explain what is difficult to explain otherwise.
Keep in mind that the accuracy of the birth time is important so that the transits on the date of the commencement of the dasha are accurate.
Transits November 28, 2005